a policy on geometric highway

8/2/2019 A Policy on Geometric Highway

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A POLICYon

GEOMETRIC ESIGNof

HIGHWAYSand

STREETS

1994

. . \merican ssociat ion f StateHigh*av and' l ' ransportat ion ff icials

{{.1 North Cupitol Street . N.lV.. Suite 2.{9lVashington. .C . 20001

(202)62{-51t00

ioCoprrilht.199.5. v thc .\rncriclrr .\ssrlciutiorrl ' St:rtcl' glirvrrind TrunsportatinOf ic ls. .\ R gli Rc'sl 'rvcrl.' I - l t

is ht tok, or pitr ts hcrerl l ' , l i l \ no t rc cprotlucctl t tn l irrntvu ' i thou t r r i t t c r ipcnr r i s s i r rn l th c pLr l r l i shc r. r in tc t l n thct n i t r ' dS tu t t : r r l ' , . \ rnc - r i c i r.

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ii i

AASHTO

EXECUTIVE COMMITTEE 1994

TASK FORCE ON GEOMETRIC DESIGN 99 4

Members

ELECTED REGIONAL MEMBERS

Region Betty Hager Francis, District of ColumbiaRegion I G.M. Roberts, Alabama

Region II Charles Thompson, WisconsinRegion V Donald Diller, Wyoming

NON.VOTING MEMBERS

Erecutive Director: Francis . Francois, Washington, .C .

President:Vic'ePresident:

Secrelary-Treasurer

Howard Yerusalim, ennsylvaniaWayne Shackelford. eorgiaClyde E. Pyers, Maryland

Do n T. ArkleHarold E. BastinJames O. BrewerDon CarlsonPhi l l ip . ClarkWayne F. CobineEugene DavillaAlan P. GlenCharles A. GoesselDon GripneDennis A. GrylickiIrving Harris, r.C. Lany KingJohn N. LaPlante

Ken LazarDonald A. LyfordMark A. MarekSteven R. OxobyRobert P. ParisiRandy PetersNormanH. RoushJohn SackstederLarry SutherlandRobert . Walters

AlabamaNL CKansasWyomingNew YorkOregonPuerto RicoCaliforniaNew JerseyWashingtonNACEMississippiFHWA, SecretaryAPWA

Il l inoisNe w HampshireTexasNevadaPANYNJNebraskaWest VirgniaKentuckyOhioArkansas. hainnan

)

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IIII r I 'IIIII HrcHwAY SUBCOMMITTEE N DESIGN-I994I

I Chairman: Dan Flowers, rkansas

I Vice Chairman: Kenneth . Affenon, New Jersey

I Secretary: William A. Weseman. HW AI

I| . l l tnhtr t Orcgon. Thonrus D. Lulry| - Pennsylvanir, rcd W. Bowscr, John J. Faic ' l la . r.I Alabamu. Don . \rklc, Rav D. Bass, . F. Caraway Dcan Schrcibcr| . l l a r l u . ! f u | L i n t hwur t e pueno Rico . o sc E . H em a ndezI Arrzonr. Frrn\ Vrilinr, Dallis B. Saxton, Rhodc sland. J . Michrel BennctrI John L L ou i s sou th Ca ro l i na , i l t i am !1 . D uBose l l

I lili:Hil}:,tt !iltss'Paul eBusk south akota. anvEngbrecht.onte chneider.

I Corontto. rmes .Siebcls, ennerh .Mauro ,.lT:Y |j:ffiTji,on, clelron ovealI Connccticut . Earlc R. Munre, Eradlcy J. Smirh, Texas. Robert Wilson, Mark MarekI Jamcs F. Bymcs. Jr. U.S. DOT, John Rice (FAA),

Dcluwure. Vichael A. Angelo, Chao H. Hu Thomas O. Willcn (FHWA)D.C.. Charles F. Williams. Sanford H. Vinick Urah, Kim Schvaneveldr, . K. Nlohanry,Florida. Bill Deyo, Freddie Simmons Hebcr Vlam

PREFACE

This Po[icy wa! deneloped t part of the continuing work of rh e Standing

Commit tee n Highways. Th e Commit tee . he n i t led he Commit tee n

planning nd DesignPolicies. as established n 1937 o brmulate nd ecom-

mendh |ghwa} , eng inee r i ngpo l i c i e s . I t ha sdeve lopedAPo l i c ' t ' onGeome t r i c

D e s i g n , l J . R u r u l H i g h w, a y s ' l 9 5 4 a n d l 9 6 5 e d i t i o n s , ' l P o l i t , l . o n A r t e r | u lHigiu'u,;s n L'rban Areui. 1957, Polit '1 ' n Design oJ'Urhan Highu'ars nd

Arltreriaitreets. gl3.Gertrtetrit 'Desigtt tuntlurclsfot ' the ational SvstemtJ .

Interstate nrl DeJ'ense igtrl1,a.ys. 956 and t967. Geometric Design tctndards

Ir r Highx'avs therThai Freeu,a'r, 969,A Potit ' t 'onGeometri( 'Design J'

'Highw:atsun d Streets,l984 nd 1990, Polit 'yon Design Stantlards- nrer-

sti ' te S,lstem.l99l an d a number f other AASHO an d AASHTO policyan d

"guide" publications.Rn eisHro publication s ypically eveloped hrough he ollowing teps:

( I) The Committee elects ubjetis nd broad utlines f materialo be covered'

iz i rrl . appropriate ubcommirree nd rs as k orces, n this casehe subcom-

mittee n'Derign nd ts Task Force n Geometric esign, ssemble ndanalyze

relevant at a an d prepare tentative raft ' Working meetings re held an d

revised Jrafts re prepared. s necessary, nd eviewed y the Subcommittee'

unrila-greements relrched. 3) Th e manuscript s then submitted br standing

Cornmlrtee n Highways pproval. nc l he n Executive Committee ppro'rll '

S t a n c h r d s a n d p o l i c i e s n i u s t b e a d o p t e c i b y a t w o . t h i r . d s v o t e b y t h e l v l e m b e rDepar tnrents e tore ubl ica t ion. ur ing he developntcnta l rocess . o tnmenls

,uere ,)ughr lt d opsidcred l 'or1 ll th e Statcs, he Fcdcral lighwal' drninis-

t ra t ion. nd cpresc .nta t ivest ' he Anter ican ubl icWorks Associa t ion ' hc

Narionl lAssocia t ion f county Enginccrs . hc Nariorur l caguc t 'c i t ics ' an d

othcr nt! 'restetl artiesThc onrnibusTrade ln d ornpetitivencss ct ol ' glJtl rncndccl) the \letric

Convcrs ion ct ol '197-5 cquircd i lch 'cc lcr i l llUcncv() c() l lvcr tt l the nctr ic

svstcnl. n response hc U. s. Depurtmcnt f Transporlation. ederal ighwll

i \ t l r r r in is t ra t i r rn ,s tuhlrs l ted cpternhcr10 . 99 6 ls hc la tc . t i r rnct r ic l t t i t l t lrl 'pllns. spccit ' icltti()lls.nr lcstirnates ir r pro.iccts ollstrtlctc(lrith icdcrel aitl '

This action cquire(l \,\SHTO t( )n]etrici]tchi s policv' .ls7.l/ I ' .r.1() Id]ILld)' .1

Pt . t t t ' r ict , i l r L .tt t, | tItt |1111,s114 | i t lnLr l ' ! ' f .T/ ( , / ' ll / ' t , ri .i .! / ) rv ls i td t lp tcdb1 . FHW.\

lu s hc stlrnd;.rrdo guitientctricconvcrsion. ollorvinghc procctlurcs)utlincd

Irbrlre, hc Tusk Forcc rl Geornctric csign nc t rr l99l to bcgin vork"hich

rcsul tc( ln rhc publ ic l t ion n l t ) t ) .1 l ' thc rr r t ' r in Scl tc te t l l l t ' t t ' i t ' \ ' t l t t t ' s' t r '

(isltrttt,tt-it' t , .si .qrts xn ildd('ndum o th c lgq0 PolicJ- tntl strbscquc'ltl) hi s

cunr.nr.,diriirrr.hi i rJivPoliivsirpcrsetleilliEirtCriiriiuidc'.{ctirrtinuirrgftitrt

wi l l bc l i r inr t inc( lrv hc Subcol tn l i t tcL ' i l r tcs ign o kccp hc Pt l l ic l .up o datc

r r th \ r turc lL ' \ ,l l rp t t tc t l t slt Scot t tc t r iclcs tg t t .

Georgia. Walker W. Scott. Hoyt J. Lively, Vermonr, Roben M. Murphy,Jint Kennerly Donald H. Lathrop, John L. Armsrrong

Hawaii. Kenneth W, C. Wong, Albert Yamaguchi Virsinia, E. C. Cmtrran, Jr. ,ldaho. Richard K. Sorensen. oug Chase

R-.E. Arherlon. K. F.phil l ips

I l l i no i s .Kcn L a zu r. D cnn i s P esc i t c l l i Wash ing ron . enn i s r ck so nInd i ana . he lp s l . K t i ka Wes r Vi rg in i a ,Noma n H . R oush ,lowa, Ccorge F. Sisson. )onald L. East, Randolph Eppcrly

Davc [-. Littlc Wisconsin. Robcr! pti , i f l t rKusas . J amcs O. [ J r cw ' c r, i c ha rd . Adunr s Wvoming . Dona ld A. Ca r l so n , av i c l . g r r r l i nKcn luc l \ . ( ' h a r l c s S. Rr r r r r c r. oh nSacks t c t l c r.

Stcvc Willirnrs All i l i t tct!qt,nr6r,rsl . ou i s i r r t r. l D unn s . Wi l l i a n r l i ckcy ' . i ck Kr l i v. r do\ l a rnc , C hr r l c s A. Vn l l c ! . Wr l t c r l cn r i ck so r r A lbc ' i l n . l l nn Kwi l r l\ l a rvhnd . S t c l c Dru n rn r. obc r tD . Doug la s s l k rng Kong , S. K . K rvc illr\\ilchu\ctts. Shcrnr.rrr jidclrnun, lfunitohr. A. Eoychuh

S t i t n l cvW. \ \ ' o r r j . Jr . l l r r un r l s l an t l s . : l i r r bc ' t hl. S r l a s l a l r l r t l r i r\ l i ch iq rn . ( ' h r r l c s J. Ar no l t l Nov l l r unswick , . l c r l r c r t ' rgc\ l i nncso t r. v r c . r n t ) Ncwl i r r rnd lu t l . ' l ' c r r rl c ( ' a r t h v\lrsr-issippi. \ 'cntlcl 1'. Ruft ' . . Richrrd Young \()r thwcst 'l 'cnitorics, 'c tcr Victr t t\ l rsstruri . jrrnL l,. ('xroll. tloh Slicdrlo Novr Scolir. )orrrld W. lhclntosh\l()ntrnn. Ronrld [:. Williarns, Crr! S. I 'ci l (hrtario. icny IVlclvli l txn\cbrrska. Donakl - . I 'urck. Flkln D, Poppc Srskrlchcwrn. lirnt ( utcfi\ cv rd r. . \ t cvc R . Or, rhv. l i c hac l V. l c l : a l l l l n t i shCo lun r l t r a .\ l c r r ' ( ' l , r r l\ r ' r r l l an r r r s h r r c .i r l h c r tS R or r ' r s\ t 'q Jcrscr. K( 'r! \ l l i ' r ton, W.tl tcr W (' .r t l icl l . .1.rl,r'r,rrr !orl'.r\ . \ t , t l r

( ' h a r l c . .\ . o c s r c l . r n t S nv t l< ' r\ c$ \ l c r t i o , I o sc ' p h ) r eh c ' c t l ,' l t r r l c sV P. f r u l r l l r \ l a s s \ l c t r o l ) l \ l ( ' ' ) l l r t r l l' l l - c r r - r r i r r r

\ . u \ ( r r l . ) c r c r ] c l l . r r r.r h r i r p . l .i l r r k , \ J f un tp r l c , \ u l l r o r t n ,A t l hu r ' \ l . r l l . r t ) t r ' .t

R . f* r r : \ . l ) c nn r r, r n l \ ) r t ' \ u t h ' ) r t l v r f \ . \ ' .' ( .l , l . r r r r S t l t n r c r l

\ ' ) r t h ( ' . r r o l r n , r.i. I t . l ' , r n r l hca r r r r.I) . R. l ) r r n t , f t r r t on \ s t r t r t t l . l l t n r l t t t t l ' n l t t ' t l

\ , r r t h [ ) . r l r r t . t .) . r \ r , lK. () Lc ' c r. t c r r ] r r s t( ) h r o , [ ) o n r i l K . l u h n r . r n . t l r r r , r , , , , r r r " r l . . n u n r . r u

I ] r r r c t u ' r l l n ( l r i n ' \ l l r r r \ ' l ) r \ t r r . n ' r l l . r ' t l r p r r l l l t r r t r

{ [l.rhornr. ]rue . i. l'.rr trr. C. W,ir nc Phrllrhcr.l \ rmo \rlcwi

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t,ii

CONTENTS

Preface

CHAPTER TITLES

Highway FunctionDesign Controls nd CriteriaElements f DesignCross Section Elements """""""""""""Local Roads and StreetsCollectorRoads nd Streets """"Rural an d Urban Arterials ' ."""""""

FreewaysAt-Grade ntersectionsGrade Separations nd nterchanges

Chapter IChapter IIChapter IIChapter IVChapter VChapter VIChapter IIChapter II IChapter X

Chapter X

Il 9

t t t

32 74t74594835 5562780 5

ChaPterHIGHWAY FUNCTIONS

Systents nd Class i f ica t ions"""""Th e Concepr f Functional lassification

Hierirrchies l lvltlvements nd Components """""Funct ional e la t ionshiPsAccess Needs nd Controls

Funct ional 1 's tem hlracter is t ics """"""""Definitions f Urban an d Rural Areas """"'Functiclnal ategortesFunctional vstems br Rural Areas "

Rurll Principal \rterial S. '"stemRural l inor Arter iu l YstemRuralCol lcctor YstemRural Locel RoildSystem

E,rfe41t Iq1q!SystcqS:: . ' : ' :' : ' ' : ': ' ' " " 'Funcrional{ighway ystemsn Urbanizcd\rcus

Urban PrinciPal rtcrial SYstem

L'rban lintlr ArtcriulStrcet System

Page

III-51S

9l 0t 0t 0I t

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l ll l


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l 5l 5

Direct ional is t r ibut ionComPosition f TrafficFuture Piojedtioh of Traffic Demands " "';' :" "'; "' ;; " "': " "'

: -r" "

SPeed . . . . . . . " . .OPerat ing Peed """ " 'Design Peed """"

RunningPeed

"""" 'Traffic-Flo*'RelationshiPsHighwaYCaPacttY

General haracter is t ics"""""""" 'APPlicationCaPacitY s a Design Control

Design Service lo w RateVersus Design Volume

Measures f Congest ion . . . . """""""

Relation etween Congesttonand Traffic Flow Rate

Acceptable egrees f Congestion """"""""Principles or AccePtable

Degrees f Congest ion """""""" 'Reconciliation f PrinciPles br

Acceptable egrees f Congest ton """"""""Freeways """""""" :""Other Mult i lane ighrvays " " """" :" '

Factors thcr'I 'han raffic Volumc'fhitt r\ 'fectOpc'ratin Condi ions

High* at ' FactorsAl incmcntWcav ing cc t i ons . . . ' . . .Rantp ennir t l l s ' . . . . . ' . """Traffic Flctors

Lcvels of Sr- 'rviceDcsign Scrvicc Fltlw Ratcs

Wclving Sect ions\ lu l t i l lnc 'HighrvlYsWithout

Cotttrol f r\cccss. \ r ter iu l t rcc ts nd Urban Highual ' s

Signirliz-edntcrscctionsAcccss Control an d Access llltnagemcnt

Th e Pei ieSir ian. ' . . . . ' . - ' " " " : ' " " " " " " : ' " '

Gencrul onsidera t t r lns" " " " " " "'Gcncr l l Char lc tcr is t ics " """""""

5 759606 loi

Urban Col lector t ree t ys tem. . . . . . . . .Local Street SYstem

Length of RoadwaY nd Travelon U r b a n ys t ems . . ' . . . . . . . . . . . . . . .

Funct ional lass i f ica t ion s a Design ype. . . . ' . ' . . . . .References

DEScN o*r?at'r:no *,,u*,oIntroductionDesign Vehicles

General haracter is t ics' . , . ' . . ' . ' . " . " ' .Minimum Tuming Paths f Design VehiclesVehicle PerformanceVehicular Pollution

Driver PerformanceIntroductionTh e DrivingTask . ' . ' . ' . ' . . 'The Cuidance as k

Lane Placernent nd Road Fol lorving. . . . . . """" 'C t r Fo l l owinS. . . . . . ' . . ' . .. ' .Over taking nc l ass ing. .Othcr Cui t lance ct iv i t ics

-l'heIn brnrnt on S.v-stctlll 'rat ' l ' icControl Dcviccs'fhc Roadwlv an d ts Envirt)nlllcnt

Intirrmation undlingRc lc t i on i t nc . . . . . . . . . . .Prirnac-vE,rpcctancy

Driver ErrorError Du e o Drivcr Dcl'icicncicsEnor Du c tl SituatitltlDcmalrds

.Speed nd Design . . . . . . .Dcsign .\sscssnlcnt

Trai t lcChar lc ter is tc s . . . . . . . . . . . . . . . ' . 'Ccnc ra l ons idc r a t i ons. ' . ' . . . . . ' . . . . . . "Volurnc

,.\vcrlr:cDaill"f rell ' icPcuk-l 'bur Trlt ' t ' ic

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Geometric esign equirements br trucks an d buses re much more severethan he y ar c br passcnger ehicres. rucks nd buses re wideran d have ongerwheelbases nc l rcatcrminimum urning aciii . hese re rr-. 'principalharac-tcristic imensi.ns f ccting horizontar.highw.ydesign. he-longer ingle_unitt rucks an d huscs cquirc 'grc i l terminimurn uming aoi i than most vchic lccombinations. ur because f their greater offtracking, he ron_9er ehicrecombinations l.so equire reaterwidths of tuming putt -.'

A semitrailer ombination s a truck ractorwith a semitrailer, itherwith orwithout ull railer. ra ruckwithon e ormore ul l railers. ecause.semitrailer-c.mbinati 'n sizcs an d tumingcharacteristics ar y wideru. h.r" ar e severalscmitruirer iesisn ehicrcs A, whecrbase. B. rength iesignatrons rc inrnctric units ' meters' n this an d n future editions of-ttpolicv ot t (icontctrit .l)e 'ri .qnl 'Hitltwot'suntl sraet.s.):( )a design

".rli .r.. . ir". . ,n,o,,u. of mediumrnlc tor- . semit ra i lercombinat ions1WB- 2) .C) a des ign enic te eprcsenta t rvefIarrrcr ractor-semitrlirercornbinations omm.nr,v n us e 1wB- r. 5 . l) a designvchiclc eprescntative f a larger ractor-semitrailcrfull trailer combinati 'ns

7 , ,: 5 i 3

. , = * l i - - - ,: 1 4 1 ; = F *; i ; ; , ' - '

A

3 - -c.tntnonl-v n us e wB - ltt). '1)a lesign ehicle epresentarive f a arger ractor-$Ilulltlilcrc'omhifrltir;nallo','crj on selectr-d iorrumh., rr..- c..J--, Tta t.nA.ssisrancccrf te'21WB e), 5 ,,t.. ;t"..";ii::#H;,:lilJn:l;rrscr ractor-scnritr.ircrgrrndfutheretr n serectecr ishwavs by th e Surtacc

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AASHTO--Ceametric Design of Highways and Srreers Des .e C ontrols cud C er s 23

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Transportation ssistance ct of 1982 WB-20), 6) a design ehicle epresen-

tative of tractor-semitrailerul l trailer-full railercombinations triples) elec-

tively n use WB-29).an d 7) a design ehicle epresentative f larger ractor-

semit ra i ler- ful Ira i ler turnpike ouble) e lect ivelyn use WB-35) .Al though

turnpike oubles nd riple railers re no t permitted n many highways' heir

occurrence oe s wanant nclusion n this publication'Th e minimum urning adii an d he ransition engths hown ar e or turns at

less han 5 km/h. Higher peeds engthen he ransition urves nd equire arger

radii ha n he minimums. he adii ar e onsidered inimum or hi sapplication.

although killeddriversmight be able o reduce hem.

Th e dimensions f design ehicles ak e nt o account imensional rends n

motor vehiclemanufacture nd epresent composite f th e vehicles urrently

in operation: owever, he design ehicle imensions us t epresent he values

critical to geometric esign an d ar e thus greater han nearly al l vehicles

belonging o th e corresponding ehicle lasses'Th e urning imensions hown n Figures I- I through I- 5 were derived y

both he us e of scale models nd computer lots or combination r articulated

units. Altemate methods an be used o compute he dimensions ha t will give

s l ght ly different a lues .The P design ehicle,with he dimensions nd urning haracteristics hown

in Figure l- l. satisfies he equirements br epresenting he passenger ar class.

Th e SU design ehicle haracteristics re suitable br al l single-unit rucks

luncimallbuses: he ontrol timensionsbr ts ninimum urning ath uffice br

a number f buscs nd ruck ornbinat ions ow n opcrat ion. Se e igure I-2 ' )

Or r rnost jrcilities crvins ruck trat ' i ic or large buses. owever. he desi-en

vchic lc i ther il rscnr i t ra i lcr ornbinat ions r argc uses houlc l c considered

in dcs ign.A se.panrtc us design vuhiclc s requircd bccause f' thc' rend ou'arcl

in tcrc i ty nt l n tns i l uscs ' i th onger rheelbr lse . \ dcs ign e ic lc cs ignated"BUS" with 17.6 nt rvhcelbase nc l tn ovcral l ength f l2 . l r n. as shorvn tt

Figure I- -1 . rt s ec n clccted. hcse i rnensions re ls o ppl icableo ubber-

t i rcd lcct r ic rol lcv uscs . l th t rugh hc rol lcy uses tr e nl y3. - r rhigh ' hcyrcrluircultproritttlttelr 5.(rtt li ovcrltcltlclcltrancc'

' l 'hcbuscs ,cr\ ltg,lpurticullrr rhln rrrea ltavno t contilnn o hc dilllcnstons

. I t ryur]n Figurc I- .1 . . \ t t x l t t t tp lcs the t r t icul l r tcd us t6 w scryi t t ! l cnai r t

c i t ics . Longcr hJ 6 col lvcnt i t lnalr t t scs . ts pr3mlal lcnt inge nclr th e ccr l tcr

; r l l t l rvsluneurcr lb i l i ry. igurc l -J d ispla ;*shc cr i t ica l l i tncnsi t l t t si r r hc - \-

BLI .S cs ign .chic lcv dcs i snc r nus l tlsr lhe uwarc ha t br ccrtain uscs he cornbina-

t i t tn t t 'grt luntl lclrr l tncc. lvcrlr l tng. t t t t l t ladrvltv crt icl t lCur! ' l l turcmllv prcsent

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36/526

AASHTO--Geometrie Design of Highways an(t Sffects

J: HLU$' 1g :yt*lq.s]lgws_rH E_r RNNG ArH o F HEAASHo DESr NX.,_Tfi"; jISLlTlj.sH9.TI.4.l:F_oJ1MELEFrFAoNiovEhiiiib-mb:ii'd

l5ll g* E_E-L^ Lq L:n FRoNwHE _ o _r_owsi{;; rnir l;URVE, OWEVER,TSPATH S NO T HOWN.

Dei i n Conii'ols a dC i:iti iia .1,

THISTURNING EMPLATE HOWS HE TURNING ATHSOFTHEMSHTO DESIGNVEHICLES.THEPATHS SHOWNAREFOF THELEFTFRONTOVERHANG ND THEOUTSIDE EAR WHEEL.TH ELEFTFRONTWHEEL OLLOWS HE CIRCULARCURVE, OWEVER,TS PATH S NO TSHOWN.

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Figure l-1. Minimum urning path or p design vehicle. Figure l-2. Minimum urning path or SU design vehicle.

2 7


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AASHTO---Ceometric esign of Highways and Steets Desipn Controls and Criteria2 7

TH|sTURNINGTEMPLATEsHowsTHETURN|NGPATHSoFTHEMSHToDESIGNVETIICiES.THEPATHS SITOWX REFORTHELEFTFRONTOVERHANG NDTHEOUiSIOEREARWHEEL.TH ELEFTFRONTWHEEL OLLOWS HE CIRCULARCURVE. OWEVER,TSPATH S NO TSHOWN.:yiHli,x.?y^s^rj-El!$!r!G_pArHsoFrHEMsr{roDEsrGRIlSrJJLr,rHglli,gF-ol1lE!EF_r;ioNi;'iE;ffii;"N;"fiEplJ:,li:#tgxF_11;..S.ql:nrnoxr-wxell'ililjws'iift.;ffiiil;

CURVE, HOWEVER, TS PATH S NOT SHOWN

EM

Figure l-3. Minimumurning ath or BU Sdesign ehicle. Figure l-4. Minimumurning ath or A'BUS esignehicle'


38/526

AASHTO__Ceometric Design of Highways and Streets

,?t,,|"e

ffi :'?:::l-,'^.::lTllerom ina ions hown nFigu es _5 h o hll"i.l: .,y_u s. ;criticformany.esisnurposes.;s;; ;6 ,h";H fi.lq-sideadius f5.9mand he urside,uA]r, ff+.L,,i"rfa O.;ffi;#;design.

Figures I-12. I I -13, I_14, an d II_15 ndicate uming paths orrecrearionar ehicles ha t shourd e considered or those ehicres.In addition o he vehicres hown n Figures I- through I- 15 , ther ehicres

ma y be used or selected pplications s appropriate. With th e advenr of:lTlur.r j:rived offtracking lots l), th edeiigner an determiteristis r he erecre,fi JJ' J ,,,#:: :;f T::J:rK'f

ine he harac-

[:ilT:: :: ::"': :::,: :::.1*' i* area he h ghwav,; i ';; ;;; :;.;;;;

Design Contrals and Criteria

THISTURNING EMPLATE HOWS HETURNING ATHSOF TH EMSHTO DESIGNVEHICLES. HE PATHS HOWN RE FO HTHE LEFT FRONTOVERHANG ND TH EOUTSIDE REAR WHEEL. THE LEFT FRONT WHEEL FOLLOWS THE CIRCULARCURVE,HOWEVER,TS PATH S NOT SHOWN.

29III

typical

Vehicle Performance

Acceleration and decereration ates of vehicles are ofien criticar parameters ndetermining ighway esign. hese ates ftengovem he dimensioning f suchdesign eatures s ntersection^s'-freeway,u*pi crimbing or passing anes, ndtumout bays for buses' The fotowing data ar e not meant o depict averagevehicles or th e design ypes, bu t rather he ow_power compact) ar or th eIoaded ruckor bus.Based n it s accereration nd decereration ates, he passenger ar serdomconrrors esign. ro m Figures I- 16 an d I- I7 , ir s obvious ha t erativery apidaccererations nd decererations re possible, rthough he y ma y be unconrfbn-abre or th e passengers nd unnecessary.. lso, du e o th e apid changes eingmide in vehicle operating haracteristics, urrent


39/526

YS-TJ{-EUFNINGPATHS OF THE AASHTO DESIGNAR E Fo R TH E LEFTFRoNTovERxllc IHoJI 'E:lF!l lnoNrwHEEt oLLowsiE iiniuuits NO TSXOWN.

I:;t

i

Design ControLys nd Crtteria

THISTURNINGTEMPLATEHOWS HETURNING ATHSOFTHEMSHTO DESIGNVEHICLES. HE PATHS HOWN RE FO R TH E LEFTFRONTOVERHANG ND TH EOUTSIDE REAR WHEEL. TH E LEFT FRONT WHEELFOLLOWS HE CIRCULARCURVE,HOWEVER, TS PATH S NO TSHOWN,

iIt'

[B:vi

f.

'Faqaes,{rs"/B ii--t tt lu-1!t lt t iI I't It fHi--lr-

ltl l

LJ

J L=r=---L'- .,- L- ll.-r i - f f i l - ffi

LL t a I rI

Figure l-6. Minimum urningpath or WB-1S esign vehicle. Figure l-7. Minimumurning at h or WB-18 esign ehicle.

AASHTO G i


40/526

AASHTO-Geometric Design of Highways and Street.s

THISTURNING EMPLATE HOWS HE TURNING ATHSOF TH EMSHTO DESIGNVEHICLES- HE PATHS HOWN RE FO R TH E LEFTFRONTOVERHANG ND TH EOUTSIDE EA RWHEEL.TH ELEFTFRONTWHEEL OLLOWS HE CIBCULARoUJVE,HOWEVER,TSPATH S NOTSHOWN.

D9qlgn Qonyy'ols ntl Ct'ireria

THISTURNING EMPLATE HOWS HETURNING ATHSOF TH EAASHTO ESIGNVEHICLES. HE PATHS HOWNAR E FO R TH E LEFTFRONTOVERHANG ND TH EOUTSIDE REAR WHEEL. THE LEFT FRONT WHEEL FOLLOWS THE CIRCULABCURVE,HOWEVER, TS PATH S NOT SHOWN.

33

,,I,r,ffi

H,/ 0t lt ttlH

r ' | 8 . ., ' , ' . t ( f , '/ / . ' . '

/ 1 . ./ / , u . '

f / tt l a

l ' a t . t/ a t , '/ ,- . ,

7--,-----:

---:::-:@--/ - t

;tPii\\\\\\. - . . I \ - - - - .

l t r . . | \- - - - - -

I' . - r

|\ \ - - -

J \ \ . \ . \ r - -\ l \ , - - -

- - - -

t | ' \ t r , ' - - X

\ i ' r , ,' ( id ' -_

l 1 \ ' 1 \l t \ \t l \ \t l \ \l t \ \I r t r t al t \ \I I \ \ .r i

t . t .

....^-..'...

-CALTRANSts.an Turntng dtu. i j \b rF ovad fq uF rLo. 'q

,l=tdarVi l

'O..le n v.iir. wdh 18.2m llll, u onndldhr.d lnIs2 surt.c. Tf$poridbn ArtLtrm. Aar (STAA)

il!'O.tlgn v.hld. wlh 14.8m trllr il rdot.d ln'19O2Surtrca TnmlDrtdton ^.3btrma Act (STAAI s;

Mlnimumurning ath or WB-19 esign ehicle.(lnterstate emitrailer)'

Figure l-9. Minimum urningpath or WB-20 esign ehicle.(lnterstate emitrailer)'

Figure l-8.

AASHTO-Ceometi( Design of Highv al r d S


41/526

AASHTO Ceometi( Design of Highv,al,.r and Srreers De;ien Conl1o$ qnd Cyireria

THISTURNING EMPLATE HOWS HETURNING ATHSOFTHEAASHTO ESIGNVEHICLES. HE PATHS HOWN R E FO BTH ELEFT RONT VERHANG NDTH EOTJISIOE REAR WHEEL. THE LEFT FRONT ^/}.{EEL OLLOWS THE OIROUL-ARCURVE.HOWEVER, TS PATH S NOT SHOWN.

35

E{IS TURNING EMPLATE HOWS HE TURNING ATHSOFTHEAASHTO ESIGNVEHICLES. HE PATHS HOWN RE FO R TH E LEFTFRONTOVERHANG ND TH EOUTSIDEREAR WHEEL. TH E LEFT FRONT WHEEL FOLLOWS HE CIRCULARUflVE, HOWEVER, TS PATH S NOT SHOWN.

,v1,'tU"

. -@"

..- ':::-""'

&.at''.r..a'

\ ' ; " \ .

\ i.'i

'\'b-i i t \ \ , .U

RT

J

t

Figure l-10.F i g u r e l - 11 .ilimum

turning path or WB-29 esign vehicle.(Triple railer) Minimum urningpath or WB-35 esign ehicle.

(Turnpike ouble raller)


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TIIISTURNING EMPLATE HOWS HETURNING ATHSOF TH EAASHTODESIGNxF,T^glE_s^Il:.1T!:.sHg'{l,4lE_FoFHE EFTRoNrvERxrrucNo xeE REAR WHEEL. THE LEFT FRONT WHEEL FOI-LOWS XE CTNCUUNCURVE,HOWEVER, TS PATH S NO TSHOWN.

THISTURNING EMPLATE HOWS HE TURNING ATHSOF TH EMSHTO DESIGNVEHICLES. HE PATHS HOWN RE FO R THE LEFT FRONTOVERHANG NO TH EOUTSTDEREAR WHEEL. THE LEFT FRONT WHEEL FOLI-OWS THE CIRCULARCURVE,HOWEVER,TS PATH S NOT SHOWN.

ti "

l-,

t-]HiTrt.tHE

0.6mMln.

Figure l-12. Minimumurning ath or MHdesign ehicle. Figure l-13. Minimumurning at h or P/ Tdesign ehicle.

!!


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AASHTO--Ceometric Dg!!g!t ol HJglUqy; qnd Steets

THISTURNING EMPLATE HOWS HE TURNTNG ATHSOF TH EAASHTODSIGNVEHICLES. HE PATHS HOWNAR E FO R TH E LEFTFROXTOVEhXNHC r.rO XE!!I]SIOC REARWHEEL. THE LEFTFRONTWHEEL Or.r-OWS XE CINCUUANCURVE, OWEVER,TSPATH S NO TSHOWN.

Q ,Sl Co!!ro!1g!! Clt terya

THISTURNING EMPLATE HOWS HE TURNING ATHSOFTHE MSHTO DESIGNVEHICLES. HE PATHS HOWN RE FO R TH E LEFTFRONTOVERHANG ND TH EOUTSIDE REAR WHEEL. THE LEFT FRONT WHEEL FOLLOWS THE CIRoUIJARCURVE,HOWEVER,TS PATH S NOT SHOWN.

39

6\t / . o t /r 9 i

/ l/ l

t / '/ / t '

/ / . t -t / t t . '

l l . /| / . t -

u

I l ' . t a -l ; . .

t l a tt ' , - t a '

t f t 2i t . t - . '

I I ^ a . '/ . - - - : -t , ' 2 7 ' - - z - r : . - - - - - -r ! t ' / \; n , / - \

/ r ' | , - - \ - -

! t ' , / , / - . e ! ! J - - _' \

," , ' , ::"

- - -o=:- -

ta- . ' .

V;'t l ^ - - -

_ ' t t- t - -

! h { . ^ . \ - \ \)Qrr^ Y \).. -\L.---'-

r \ l\ \ l

I. \I

...s

\g^t'! 6 . 1 .r-s

I l . r. , a . 6 r l t . r i t ! . t r r r I, . : , , : .

rTn ffi'La L / rc^lirsnn

Flgure l-14. Minimumurning ath or p/ B design ehicre. Figure l-15. Minimum urning at h or MH/B esign ehicle.

AASHTO--Ceometri(. Design of Highv,ay.s nd StreetsIII

d


44/526

g , y nd Streets

IQgltsl Cqr!;'o!s a1d Qy4erys 4L

sou.c.rvlchtgon regor l NcHRp 70 o! dcvoroped by Ny 0.0.I.(J2)

Figure ''r6. Accereration f passenger ars, ever onditions.

Pollution rom vehicles n the orm of noise must also be ecognized y th ehighway esigner. o ise s unwanred ound, subject ive esul t f sounds ha tin t rude n or n terfere ir hact iv i t ies uc h s onversar ion,hinking. eading, rsleeping. ound an exist without people-noise cannot.

Motor vehicle oise s generated y the unctioning f equipment ithin hevehicle, by its aerodynamics, y the action of tires on the roadway, nd, nmetropolitan reas, y th e short-duration ounds of braking squeal, xhausrbackfires. oms, an d sirens f emergency ehicles.

Trucks an d auromobiles re the major noise-producing ehicles on thenation's ighways. otorcycles re actorto econsidered ecause f he apidincrease n their numbers n recent ears. Trucks, particularly eavy diesel-powered rucks, resent he most difficult noise problem on the highway. hedevelopment f more powerful ngines as generally ncreased oise.Modemautomobiles re elatively quiet, particularly at the ower cruising speeds, utexist n such umbers s o make heirtotal oise ontribution ignificant. steepgrade as ittle nfluence n he noise f automobiles ut ca n cause n ncreasein noise evels or large rucks. Noise produced by automobiles ncreasesdramatically with speed. Unlike the automobiles, ruck noise evels are essinfluenced y speed ecause he actors including cceleration oise) hat ar enot at-fected y speed irectlyusually make up a major part of the otal noise.

Fo r passen,eer ars. noise produced nder normal operating onditions sprimarily io m the engine exhaust ystem an d the tire-roadway nteraction.Under high-speed ruise conditions, he dominant source s from the tire-roadway nteraction. or conditions of maximum acceleration, he enginesystem oise redominates. ar s at constant ighway peeds iv emuch he amenoise reacling hcthcr or not the engine s operating, ecause he noise sprincipallvproduced v the tire-roadway nteraction with sonre added windnoisc .

Truck noise as everal rincipal omponents riginating ro m such ourcesas exhaust. ngine ears, ans. and air intake. At higher speeds, ire-roadwar'interlctionan d wind noise dd o the problem. As in passenger ars. he noise

produccd y argc icsel rucks s primarily iom the engine xhausr ystem ndth e ire-road*lv nterlction. or rucks. owever. ngine xhaust oise ends odominate irc-roldwav nteracrion irrmost perating onditions. hi s s panicu-larlv rue durins lccelc'rrltion. major source f the noisc of large rucks s rh ecxhaust tack.

Thc' urlin ot ' the noise aries with th e number nd opcratinr onditions t'th e vchic les ; he direcr ional i rv nd ampli tude f the noise r rl wirh hirhrvaldcsign eatures. he highway designer must herctbrc e concerned irh ho *

rghwty ocations nd dcsign ntluence he vehiclc noise erccivcd y persons

2OO td^

P^SSEI6R crns - osrrrcE100 5OO 600

IR^VELEo r,rEns

U)r{ r r oS c1>9 - sr 8Uts 70;

: ;L 6

F ;

if F

- + .E

r a C a=a l =r a = !' ) E a X

7 . 4 =

> ! - Jt Z r . . -- _ 7 tt t = -

a - = ;9 t = "

< i u .

- -t j . < =

' ! i . z+ i + >t ; t =- L > - a

' - t ! -+ : . i i : J

i ! : 2 42< < 4 Z i

. - => : O - 9 3 . N

, i ; i .E= Tai.j ; ElZ

iei'ilza:l?i!1;*AV17t1;efE!=rs,:, EE:i$afs:i:isii;E3;

a

- ' eo :

- / : uY. i 1; ! ! a kF l i ; iI - 7 . -. . . = i > i ) ! g iE ; - " - ' 1

' 9 9 ? o c; : ; > nd 3 ; < 5

= =: c . : xr t - - _ => - = . -

. = > . = =Y /. , r.c t J - ?

. F . = .= - 7 = i: 3. ! "'u7 - - r rJ a t : > e

d . i i < ;

- - C

: - 3 - : 3 9j * = Z 4 Ei ^ 1 - ' ' -

= = - a - -

= . 4 = P ?J ! ^ = i 4: - = l ' -i " r a : : -1 ) = , i 4


69/526

f O"* "n*, "r sen;ce r. ueen etecrea, r is desirable har lt etemeirrs f

Weaving Sections

| *e reaa*av are ons rnily designed o this evel. Thisconsisrency l designL leryice ftow rare esulrs n n"ur"on"tunr ieedom of tlafli c movement nd weaving seclions {cur where ne-way affic sreams ross y merging nd

I ope ar nP peed. nd now nte nuolions iom borrtenecks an be avoided. divergingmaneuvers. he ptincipal ypes f weaving ections re lluslmied n

I t* iiv ttty suppt;es he nrtyricat base or design atcularions nd Figure I-26. weaving ctions re designed. hecked. nd adjusted o hath

I dec ! ons. ut he es gnermust se rs r herjudgmenr oselecr he roper evel levelofservice s consisteflt ith the emaining ighway The design evelof

Iof service. he designer ay possibty

elect design ervice low rate ess hanservice f a weaving ection s dePendent n its length. number f lanes.

rhe anricpated mand or cenain ecreational cures f fo. environmenral ceptable egree fcongslion, nd elativ olumes f ndiv dualmovements.tanduse lanning easons. r. fie guidance iven n Table I-6 may be chosen Large-volume eavinS ovem$ts sually esult n considerable rictionandfor the aporoorirle atues n oanicilar ocatrons. reducdon n sped f all raffic. Funher, here s a definite imit o he amount f

Wlerirer esignrng n nrenecrion. n nierchange, nanerial, r a rccway, traffic hat an e bandled na givenweaving ecdon ithout ndue ongestion.

f- rte setection f rtred;sirEd evel of ser.vice mu$ be carfully weighed bcau;e This limiting volume s a function of the distribudon of tmflic between herhe adequacy fthe rordway s dependenl n rhis choice. : weavingmovements,he ength f weaving ection, nd he numtr of lanes

meretr.

Type nf Area and Appropriate Level of ServiceWeaving sections may be considered s simple or multiple. Figure I-27

shows simpleweaving ection n which a single-entranceunction s ollowedby a single-exit unction. A multiple-weaving ection onsists f two or moreoverlapping eaving ections. multiple weave may also be defined as ha tportion of a one-way oadway ha t has wo consecutive ntrance unctions

followed losely y one r more xit unctions, rone entrance unction ollowedclosely by two or more exi t unct ions , s shown n Figure I -28 ' Mul t ip leweaving sections ccur frequently n urban areas where here s need orcollection nddistribution f highconcentrations f traffic.For urther ntbrml-tion concerning he operation nd analysis f sirnple an d ntultiple weavingscctions eler o the HC M ( l) .

Th e *'eaving ection hould ave a ength nd numberof anes aseti n heappropr ia te evel f service s given n Table l -6 .Th e HC M ( I ) presents nequation br predicting he averagc unning peed f wcaving nd non-weav ngtraffic based n roadway and raftlc conditions. evel-of-scrvice riteria il rweaving ections re based n these verage unning peeils.

illultilane Highrva-vsVithout Control of Access

These igh*a).smcv be retted as reeways f major crossroads re nfrcqtrcntor ar e separi.rtedn grade rn d f marginal dcvclopment s so spcrs ls ttlgenerate ittle ntcrt 'erence. ve n on those ighways wherc hc ntcrlc'rcrtccscurrentl) 'onl)marginal. he dcsigner hould c alert o he act hlt b.v-he design

C C

C L

D

In nrost cilsL.s he designer hould assutnc ihcrul crossroad nd busincsrimprovcmc'nts vc r hc design it e of thc aci l i ty.

HighrvayType

RuralLevel

RuralRolling

Rural Urban ndMountainous Suburban

Freeway

Arter ia l

Col lec tor

Locul

C

l)

D

D

D

NOTE: Gcncml pc r l t in r ond i t ions ir r cvc l s f sc rv icc Sourcc : cf . ) :.\ - trcc low. rvith ow volurncs nd high spccds.B - rclsonublv ir:c low. but spccds cginning o bc estnctct l y tral ' f ic

cond i t ions .C - in st lblc ' br v zortc, ut rnost r ivcrs cstr ictcd n fhcdom to sclcct hcir

() \ \ 'n pcc(I .D - lpprolchinq unstablc lorv,drivcrs ravc i l t lc frccrlorn o mtncu\cr.E - Lrnstlrblclo 'uv.nav tc shrtr t toppiu.lcs.

Table l-6. Guide or selection of design levels of service.

IIItI

DS S!! 9!!!r ok qt {Q1 1e ra 93A4 SUTQ4 eoJn i c Dc jg alf U ghy gysg nLS ee s


70/526

Ijt

I

Figure l-27. Simpleweaving ection.

y|r1llrl. f rcvlng

Figure l-28. MultiPleeaving.

Where here re major crossroads r where marginal evelopment esults n

rnore ha n slight nterference. he facility should be trated s a multilane

highway withoutaccess ontrol.

Arterial Streets nd Urban Highrvays

Arterial treets nd urban ighways rea roublesome lass f highway io m th e

sttndpoint festablishing esign ervice lo w rates. he eason or hi s s hat he

lcvcl of service rovided by such acilities does no t remain stable with the

passage f imeand entls o deteriorate n an unpredictablc anner. he capacitvof un arterial s generallv ominated y th e caplcitv lf ts ndividual ignalizc'd

intcrsect ions . evel of service f an ar ter ia l s a tunct ion f aver lge ver l l l

travel Speed ve r a section f th e anerial.

Signalized ntersections

Dcsign apacities f signalized ntersections re subject o a very arge umto*rtr fvuriables. tt he ertent hlt thesc' ariablcs an be predicted br condititlns ts

I

tIIIIl

1

Figure l-26. Weaving ections.

IAASfll O4


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II| ,hey are ikely to occur dur ing he des ign ear, des ign apaci t ies an be

| . t t imated by procedures iven n the HCM (11) ' In tersect ion esign an d

I rpacing hould e coordinated it h he raff ic ignal es ign nd phasing.III

.ICCESS ONTROL NDACCESS ANAGEMENTII ne resulated imitation faccess scalled ccess ontrol.which s achieved hrough

I ,f-1eeg-ulation f public access ights o and rom properries buning he highwayI t.cilities.These egulations enerally recategorized s ull control faccess, artial

control f access, ccessmanagement nd driveway and approach egulations.Full control of access means hat preference s given to through raffic by

_ providing ccess onnections nl ywith selected ublic oads nd by prohibiting' crossing t grade nd direct private riveway onnections.With partial control of access, reference s given to through raffic to a

degree hat. n addition o access onnections it h selected ublic oads, heremay be some crossing t grade and some private driveway connections. ull orpartial ccess onrrolgenerally s accomplished y legallyobtaining ight-of-access ro m he abutting roperty wners usually t he ime of purchase f th eright-of-way) r by the use of frontage oads.

Access mana-qement nvolves providing (o r managing) access o landdevelopnrent vhi le s imul taneously reserving he f low of t raff ic on thesurroundin-rIoa d systenr n terms of safety, capacity, and speed. Access

llranugenrent" as merged ve r he ast ecade s a ne w philosophy f"accessTonrrol" ha t ppl ies o a l l ypes f roads nd treets . t ca l ls or se t t ing cccss- standlrds ir r various ypcrs f roaclway, eying designs o these standards,

huvi lg rh c access tan(!ards ncorporated nto legis la t ion. nd having hc

l cg i s l l t i on p h e l d n he ou r t s .Acccss l tn i lgcntcnt iews he highway nd ts surrounding ct iv i t ics s

pl r t o i r r ins lc . svs tcnt ." ndividual ar ts f the system" nclude he act iv i ty

center nt l it s c i rcula t ion systems. ccess o and from the center. hc

avai labi l i t l oi publ ic ranspor ta t ion. nd he roads erving he centcr. A ll

ptrts lrl ' rnp(')rtlllttnd nteractvitheach other. Th e goal s to coordinltc hc

plunning nd . ic .s ign f cuch center o preserve he capaci ty f the ovcral l

s\ stcnr, nd o lllorv efficient access o and ro m th e activities..{ccessmlntgernent xtends ratflc engineering rinciples o th e ocation.

.lcsisn n( i oLrcrutionf access oads erving ctivities long streets nd high'rrur s . t ls o ncludcs vlr luat inr :he ui tabi l i ty f a s i tc br given leve opmcnlsl ' ronl ln :rccess tuntlPoint

Drircr r tr or rcgulations ay be applied ve n hough o control f

.rcccss s ohtuincd. lch abutting ropeny s permitted ccess o th c slrecl or

high\\ . l r : horrcvcr, thc location. nurnber. an d geometrics of the acccss Flolnlsnrlr l^ *rorcrnctl bv th c rcgulations.

Th e principal dvantages fcontrol ofaeeess re he preservation r upgrad-in g service nd safety. ully controlled ccess ighways r streets av e no at-grade rossings nd have arefi.rlly esigned ccess onnections. highway rstreet with partial ontrol of access as similarcharacteristics o one with fullcontrol bu t ncludes ome rossroad ntersections t grade an d some arefullyselected nd predetermined an d service onnections.

Th e principal perational r f 'unctional ifference etween street r high-wa y with or without ontrol f access s th e degree f interference it h hroughtraffic by' other vehicles r pedestrians ntering, eaving, and crossin-q hehighway. With control f access, ntrances nd exits are ocated t points es tsuited o it trafficand and-use eeds nd are esigned oenable ehicles o enteran d eave afely with a minimum of interference it h through raffic.Vehiclesare prevented rom entering or leaving elsewhere o hat, egardless f the ypean d ntensity f development f the oadside reas, high quality of service spreserved nd he accident otential s lessened. n streets r highways wherethere s no control faccess nd oadside usinesses evelop, nterference ro mthe oadside an become major actor n reducing he capacity. ncreasing heaccident potential, nd eroding he mobility function hat the facility wa sdesigned o provide.

Controlof driveways nd oadside evelopment s an ntegral ar tof accessmanagement. f access oints ar e adequately paced nd entering nd exitingvolumes re ight , he s t reet r h ighway unct ions ff ic ient ly. f access ointsar e numerous an d ntering nd exiting volumes ar e heavy, he capacity ndsat 'ety f the acilityare educed. owevcr, rade-offsmust be made o servethrough raffic development ncl and-use eeds, articularly hose nvolvinginclus t r ia l ,omrnercia l . r o ther igh-usc s tabl ishments .

A ne* rura l h ighway without ul l control of access eneral ly as ewintersect ions r roadside us inesses nd he tcc ident at e approxinla tes ha tof a f reerval ' . With t inre , businesscs nd interscct ions ncrease nd th eluccident at e ma y double r t r ip le as shown n Figure l -29. Over i rne . hcfrceway accident a te emains he same r may even dccrease l ight ly.Ful lcontrol of access s the most mportant ingle safc ty actor hat may be

dcsigncd nto nc ' rv ighways . t i s the key t lc tor in the outs tanding afctyrccord f f reeways 2) .

Fo r highway's vithoul ul l control of acccss. echniqucs rc al 'ailablc oprovide ddi t ional a tery J) . The most bvious echniqu. 'imi ts hc ' umber fdrivewa r s and ntersecticlns. ther echniques uggest hangcs n hc design ndopcrational ersures oth within and outside hc highway ight-of-wav. hetcchniques im to mcet hcse lnctional objcctives: ) lirnit the nurnbcr tf

tion equiremcnts, nd .1 ) emove uming vehiclcs rqueues brcr'rtain ortionsr l l ' the hrouqh ancs .

!

F 9- AtstTo:eieanarftaesig,t ofnishffirffind sr-cets D


72/526

Lor" 0."r. . of access onrrolor ccss anagemnrhould e nctudedn th'r s eaqible r ult imarelyossible le \ 'gnificant aclon n defining he

I ,fr"t"""foorn""tofany s1rct r highway. anicuiarly new acilitywhere h type of \lreel or highway

L tit"lit'ooa

of"ornmercial

development xists. he ype of strel r h Shway

I bc buih should e coordinated ith the ocrl land useplan o ensure har he

I desired onrrolofacce ss an b maintaindhrough ocal oning rdinances rTHE PEDESTRIAN

I subai"isron cSulations. he control of rcces\ mav rrnge iron mrnimum

I dri""*av,"gutulionso ull control. hus he extenr nd degre f access onirol Ccnral consideratioos

I

I n pedesrrians an y erson foor.andnvolvement fpedstnansn raffic r

a majorconsiderarion n highway lanning nddesign. edestrians rea part

ofevery roadway nvironmenr, nd ttention must be paid o hei presencein rural as well as urban areas. The urban pedestrian. eing far more. . - . . 5 o o f f i p r e v a l e n t , m o r e o f l e n i n f l u e n c e s r o a d w a y d e s i g n f e a N r e s t h a n t h e r u r a l

Dedestrian oes. Because f th e demands f vehicular raffic in congested

S r o f f i ; r b a n a r e A s . i t i s o t i e n e x t r e m e | y d i f f i c u l t t o m a k e a d e q u I l e p r o v i s i o n s | o r; l l l l l l r r l ll l l l l l r r l le I I I ar-orod6 hre.sicltons 6e. xlomei.. I Oedesrrians. et his must be don.because

edestrians re he ifeblood ol

! o o f f i o u r u r b a n a r e a s . e s p e c i a l | y i n t h e d o w n l o w n a n d o t h e r r t a i I a r e a s . I n g e n e r r I .: | | | | | ,),----ff | | ,he mosr successful hopping sections are those rhat provide he most

i ' ' o f f i c o m | o a n d p t e a s u r e f o r. p e J e r r r i a n s ' P e d e s | r i a n t a c i l i l i e . i n c | U d e s i d e .s " - - f f i u l* J | k \ . c ro \ s $ : c Ik r. r r a f f i c c on t ro l | e a tu r e s ' spec i a Iwa l l . 11y : fou ld : l ] i o l :i n o f f i P o r t i o n s o f f r e e $ t l } r i g h t . o f - w : r y ' a n d c u f u c u ( s ( d e p r e s i i o n \ l c n d r r m p \ f o r2 L_l---1-1 )___ffi; I ihcotd, arr.crs lnd ersons ,rhmobirirympxirmcn(s.hc! rre Jrso

a' i

7 , , o f f i . t | ' h u \ v o p { o l o l h e l I o . l d i n 8 . I r c ] s ' 8 r l d e s e p l r a t i o n s . n n d l h c ' t l | r s o r3 | | I | | -L - - - - f l ' l c s c i r l u r ( ) r s r c l r r c ( l( ) t he sc f ac i l i t i e s .

b 'zooq

! rsol t L':-t

I L'f : J tieneralCharacteristics

0

F,^m | | I I I l l ti ,c rl 'crlc \ ptunrn,l eiisn edertri3nrcilires . r i ncccss.rrl, , cs(ribelr(5 ' o f f i l y p i ( I l p c d e s t r | n ' T h e p e d e s l r i 3 n w | l l m o n l i l i e l y n . ' t u . t | k o v. r I ' 5 | m l o $ o r |

: I | | I I I | | | | i , rovL.rr.okmro(rrchrbus.irndabourtl{)percentdlrhcdistnncAtnlelcd$il l. 5 0 f f i | | | h c | c s s | h J n l ' ( l k m l l { ) ' I h c t y p i c J l p t d e j t r i i \ . l j h o | F r l l b o u t 5 t ) p c r | j c n l o l

I L | | I I I | | | (hc imc hxr c or shc s r pedcsrrirn nd commutcr nly ,bottt I ptrcentr

o---f--;-----;--; .o ,, .o,hcrinr.As.rco sequcnc':.., kn of pedcstri.rn olumcs nls r rbour noonmlh':f lun rt lhc comnruler trk times. lypicalplot flhc houtlJ luctuutrorr\

Numbor of Bus lnesses Dor Kl lomote r i' l t cdcs r r i ln . lumcs on ac l ty s t rcc t s shown n F igure l - .3 t ) .' l '5cpcdcstr i i ln \ ' () luntes ar c intlucnccd by such trlnsicrrt ctr t t t l i t torts t:

\ \ c r t thc r r. in spcc i f i c oca t ions ' dvcr t i scd a lcs '

ls arc lcss table than those ot 'm()torists . l l tny- pctlcs-

triuns onsidcr hcntsclvcs utsidc he aw n trafl ' ic lattcrs. lnd n llrrrlv rl5cs

l lcr lcs t r i lneguiar ions rc n() t u l lycnfbrced. hi s makes t d i i f icul t tl lcs lsn t

lrrcrlin ir rsatr ' trtd rclcrly cdcstrtan ()vctllcllt '

A -Crode ln te r s c t lons ) er Kl lore r

1C

q

4

l

C)

Figure l-29. Accident rate on 4-lane divided non-lnterstalehighways by number of at-grade ntersectlons erkilometer nd number f businesses er kilometer '

AASttTO-Ccomctri( Desigtt oJ Hi,qhu'ays nd Streets Dc.rienControl.s nd Criteriu 99


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ns end o walk n a path epresenting he hortest istance tween wopoints; hus. long treets. he yofien ross ridblock nd ail o stay n crosswalks.

Pedestrians ls o av e basic esistance o changes n grade r elevation hencrossing oadways and tend to avoid using special underpass r overpasspedestrian acilities. lso. pedestrian nderpasses ay be potential rimeareas.

An important actor n relation o pedestrian ccidents s aee. Very younepedestrians re often careless n rafllc iom ignorance nd e.ruberance. hereas

th e elder ly ar e aff 'ec ted y l imi ta t ions n sensory. erceptual , ogni t ive . ndmotor skills brou_sht n by the aging process. edestrian ccidents an also berelated o the ack of adequate idewalks, hich brces edestrians o share hcpavement with motorists.

4 6 8 r 0 t 2 2 4 6 8AU PtI

T i m e o f D a y

The follo*ing have been Cuggested s measures it h potential o aid th eelder ly edest r ian:

Use imple es igns ha tminimize ross ing idths nd minimize he se fmore omplex lements uch s hannelization nd eparate urning anes.When these eatures re necessarv. ssess ltemate designs ha t willprotect lderlypedestrians.

Assume ower walking peeds .Provide efuge slands f sufficient width at wide ntersections.Provide ighting t ocations hich equiremultiple nformation atheringan d processing, nd eliminate lare sources.Consider he raffic control ystem n th e context f the geometric esignto assure ompatibility and to provide adequate dvance waming ofsituations hat could sumrise or adverselv affect the safetv of elderlydrivers nd pedestrians.Us e enhanced tandard rafficcontrol devices.Provide versized, etroreflective ignswith suitable egibility.Consider ncreasing ig n etter iz eand etroreflectivity o accommodateindividuals it h decreased isual acuity.

Us e properly ocated ignals with large ignal ndications.Provide nhanced arkings nd delineation.Use epetition nd edundancy.

Physical Characteristi"r, . . . . .

Ild-y Area

'Ihc phvsical dinrensions f the human body are retlected n the design ofpcdestrian acilities. or he design f sidewalks. tairs. etuge reas. r transit-loading reas. knorvledge f the wrdth an d depth of the body or the eft 'ectivehotlv rrc.as nrost sc'ful. tudics ave hown hat nearly all adult males have tsltoulticr ' ir. l thess hln -51-5 tn rantl a depth ot ' less hl n .130 nrn. For dcsignpurposcs, he area f a body s pproximated y an ellipse (X)mr n wide an d 1-5()r r r rn cc p 16) . These minimum dimensions pplv onl ;" o s i tuat ions vhereindividuals re fbrced nto close proximity. f a greater cqreu' l comtirrl orrnobilitv s rcquired. larger bodv arel per pcrson must bc lssumcd. Oldcrpctlestrians ra yneed o us e eancs r walkers o assist hem n walking. Sonrepcdestriuns ay have aids such s shopping ans or baby strollerswith thcm.

IR

t6

o t )o

xl n

o ' v

); o

to

Figure l-30. Weekday verage ourlypedestrian olumes n cityst reets 15) .

I 'hcsc r- 'vices lv increlse he eftcctive ldv area br usc n dcsign.r\ s desired edcstrian nobilitl ncrcases, pacc o qo around slowcrmoving

pcrson r o avoicl n oncoming r crossing crs()n us t be availablc. s curbs,

Desig,n ontrols and Criteria 1 01III tOO AASHTO--4eometric' Design of Highn'a4's nd Streets

I


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IIf stairrrcr other rregularities o the ground surface are encountered, t east one

|0" . . or one ta i r-s tep eparat ions required or normal walking.

I

II Walking Rate

I There s a broad ange f walking speeds mong pedestrians. he rates when

I crossing street re significant n design. verage walking speeds ange romI approximately 0.8 to 1.8 m/s with the Manual on UniJorm Trffic Conrrol

I DevicesMUTCD) (3 ) assuming normal walking at e of 1.2m/s.Older people

I will generally e n the slower part of this ange.I Walking rates are aster at midblock han at ntersec tions. re aster or men1., than women, and are affected by steep rades. Ai r temperature, ime of day, rip

purpose, nd ce and snow all affect he pedestrian walking rate. Age is the bestidentified ause or slowerwalking ates, nd n areas here here re many olderpeople, a rate of I m /s should be considered.

Walkway Capacities

Figure I-3 shows hat walkingspeeds ecrease s he pedestrian ensity f thcwalkway ncreases. igures I-32 an d I-33 show hat at an optimum peed nddensity. he walkway willcany he argest olume. he eft 'ective idth usecl brrvallw+ycalculations us t be reduced hcre parking nc'ters. yclrants. cws-

--------- SHOPPERSoidor)- CoUVUTERSFruln)

STUoENTS Novln' hoolcr)

+=--\++;i ==_

Figure l-32. Relationships etween edestrian lo wan d space'

. . . . . . . Stum.rt l o d . r ,- Co.Wl..t lFrutd- - - - . S t u d . n t r t i lovl^, t t u . l c . ,- - futf, .60. ot ob.t'voild

I

I

. . 'z

t- - - - - s r l s . { @ l- - ' - Cffi tr. f r d d- srd FF lkro--- 9 1 ! & r. kvh d h*t. - - ' - ' - - t u r f , nry ot h f v o t l d'rffi crrcttr . & N/htn/dre

^ r( n

=z l? o

Ss o

d o uF

: i ooU O

6

F

z

d , U

F

2

DENSITYPERSONS

1

PE R SOUARE METE R }J0 60

FLO| (PERSONS90 tZO t50

PER MINUTE ER METER F TIOTH}

Figure l-31. Relatlonships etween pedestrian peed an d density' Figire l-33. Helationships etween edestrian peed nd tow.

Design Controls and Criteria t0 310 2 4$4U--4,oUe!ic DesiIn of Hig!1ways nLs!!rc4


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atan&, itter banels, itilitypoles, r similarobstructions reclude he uie of th efull walkway. Walkway capacity alculations or sidewalks, or stairs. nd orthe effect of traffic signals nvolve different procedures s discussed n th efol lowinsmater ia l .

Sidewalks

To quantify he elative mobilityof th e pedestrian nd hi s or he r conflictswithother pedestrians ha t nfluence is or her walking speed. maneuvering oom,and feeling of comfort, degrees f level of service have been ntroduced 17).Similar o he evel-of-ser"'ice oncept iscussed arlier n his chapter nd n heHeM (f f ), levels of service A to F) reflect ncreasing rowding and decreasingfreedom ofmovement. These are based n the available area per person nd aredefined n the ollowing wa y (18):

Level-of-service A provides an average of 12 m2 per person or more,allowing each person o choose desired walking speed nd o avoid conflictswith other pedestrians.

Level-of-servic'e , within the range of 4 to 12 m2 pe r person, edestrians

begin o be aware f other pedestrians.Level-rtf-servic'e . equivalent o an occupancy ate of 2 to 4 mr per person,

requires minor adjustments o speed and direction by pedcstrians o avoidconflicts.

Lzt 'el-of-sen'ic 'c . with an occupancy f 1.5 o 2 mr pe r person, reedom o

select nclividual alking speed and bypass other pedestrians s restricted.Frequent hanges n speed nd position re equired.

Level-of-sert ' ice . equivalent o average ccupancy i 0.-5 o l '5 rn : pe rperson. rovides or very cro"vdedwalking, at times reduced o shuff ' l ing.rnaking everse r cross-traffic lo w very difficult. The speed f virtuallyal lpedestrians s reduced.

Level-o.f-.sert ' ir 'eprovides n area of occupancy f less han 0.5 m: pe rperson.

twhich evel pc'rsons ikely o be standing tationary n a waitinsarea

or s able o walk only by shuitling. here s tiequent, navoidable ontact it hother edest r ians .

Computations li rvalkwal capacity must us e walkway widths that arercduccd bout fi) mr n f there re adjrcent walls. plus an additional lX) mm frvindow shoppers re expccted. trect hardware uc h as parking meters ndpoles lso reduce he avai lablc alkweywidth .

Intersect ions

When pedestrians ncounter n ntersection, here s a major nterruption. he

sidewalk hould rovide ufficient torage rea or those waiting o cross lu s

area or cross rafflc Io pass.Once edestrians regiven he walk ndication. he rosswalk idthbecomes

important. he crosswalkmust be wide enough o accommodate he pedestrian

flowin both directions ithin he duration f th e pedestrian ignalphase.

If th e ntersection s not signal ontrolled r if stop signs o not control he

throughmotor vehicular raffic,pedestrians us t wait or sufficient ap s n the

traffic to cross.

Characteristics of Persons With Disabilities

Fo r the designer o adequately rovide or th e person with disabilities. he

designermust be aware f the ange f mpairments o expect o ha t he design

ca n provide or hem. n this wa y he mobilityof this sector f our societyma y

be greatly nhanced. he designer s cautioned o adequately eview al l local

an d national equirements o assure roper compliance with all rules an d

regulations. or urther derails ee hapter V section Curb Cu t Ramps."

Mobilit .v mpairments

Arnbulation ifficulties ange 'ronl pcrsons vho walk unassistc'd ut "vithclifiiculty.o pcrsons ho ecluire ic l iont braces, anes, r crutches. o persons

confined o w'heelch;rirs. tairs. urbs, nd aised hanneliz-ingslands re hc

rnajor oaduay obsrructions o these edestrians. esign modificationsmust

provide amps athcr han stlirs lr curbs. hc tiont wheels f a wheelchair re

very sensitive o obstacles. ncl any burnp rnay impair th e progress f a

wheelchair r ncrc lse he poss ibi l i tv f he over t t r rn ing f a vheelchair ovtng

tirrward.

Visual rnpairments

pcde tr ians rh cr.v inr i tcd is ion equire pecia l onsidera t ion.ntc ' rsect io t ts

ar e he nrajor hrcltt o thcir satl ' t1 Cornplic:.rtcdrossinss uc h s thosc Jt

c n a l l t l c l l / - c u l l l l c l . \ ( : L l t ( r l t t L d t l l r s d ) ) r r r L u u - ! r L ' \ r u r ! \ r v *" -- - t - ' - '

s ions it r whc.c lchai rsnakc ocut ing hc curb inc dif t lcul t br th e bl ind ant l r

rcx tu r ingoro thc r ind ic l t ionr l f h i s r r rc r tn l tvbco l ' a s s i s t ancc .Bc ' c l tusec ross l l l ! \

AASHTO--lieometric Design of Highways and Streets Desi,qn ontrols and Criteria r05


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n made y th e sound f traffic, autionmust be used when xclusive trrnphases r other unusual raffic movements ay confuse he blind pedestrian.

Deu"top."ntal Impairments

Many people with developmental mpairments re unabre o drive an d ar etherefore often captive pedestrians. o help ensure he correct esponse

romthese pedestrians, ncluding young children, he pedestrian ignals or otherpedestrian-related acilitiesmust be simple, traightforward, nd consistent ntheir meaning.

Conclusions

Design of urban highways should nclude considera t ion f methods ofincreasing efficiency of operations n areas of heavy pedestrian-vehicularconflict. Major forms are he ollowing: ) provision of pedestrian ubwaysor overcrossings, 2) the conversion ro m two-way o one-way street pera-tion' (3 ) elimination of turns, (4 ) provision of separate ignal phases orpedestrians, nd 5) elimination of some crosswalks. hese an d other oedes-trian considerations re covered n subse


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Toral accidenrs rounded;Faral accidents oundd)Non.faral disabling

in1ury ccidenrsPropenv damage ccidents

( n c lu d i ng on -d i s ab l i nginjury accidenrs,r

Deaths

Total

Motor Vehicle Traffic

Vehisle regisreredMotor Vehicle

17.000.000 15.600.rx)0Jr].ti(x) ,19.900

| .100.0fl) t.2{D.ffx)

r5,600,u)0 t5.lg).0(x)

It9,38.r.000 rlg.un,ft{)

2,G10,76r ?.r 15.015

' li.7(n.l(n I 1.,1rD.00,0"JI.lr)(.) .38 .{00

1.9.10,r7rJ t.fin.000

r5.7(X).(xx) r0.l(n.cu0

J6. l (X) J l .5m

| 76, 9 l19 | 9.1.tt97.fin

1,95'7.128 3.176.088

I1.700,000.14.500

t,300.0(X)

l:.500.ux)

-52,900

e6.887.m0

Th e most significant esign actor ontributing o safety s the provision ffull access ontrol. he beneficial ffect f hi s element as been ocumented nreports f the cooperative esearch tudy 24 ) between he FHWA and 39 Starehighway gencies. ne of the principal indings f this study s har he absenceof access ontrol nvariably ncreased he accident ate.

The study' 2.1) hows hat accidents, njury, and atality ates n Interstatehighways re between 0 and 76 percent f comparable ates f conventionalhighways xistingbefore he nterstate ighways were opened o traffic. Noother ingle esign lement an claim comparable avings.

A study 25 ) of rural oads hows he elationship f accidents o he numberof access oints. Traffic conflicts were defined n the study as he number ofminor road ntersections nd principal access riveways o abutting propertybetween major oad ntersecti ons hic h were used as he break points betweenstudy ections. Se e Figure I-34.)

4. 0

2. 5

?.CI

r6Trofflc Confllcts

9 t?p6 r Kllomefcr

5?.0(xl .15.600

k i lom e te r s ( m i l l i ons ) 1 .552 ,897

Rates

Motor vehicle deaths er | 00mill ion vehicle kilomerers

Motor vchicle accidents cr I(X)mill ion vehicle kilomcrcrs

* NATIO N AL SAFETY COUNCII -"* U. S. DEPARTI,IENT OF TRANSPORTATION

Table l-7. Highway accident statistics or five typical years.

I t s sc ' ldorn ha t an accident esul ts rom a s ingle ausc . ' rherc rc usual ly,several nl luences ff -ect inghe si tuat ion tan y given irnc . hcse nf lucncesca n be separated nt o hree roups: he human lement . he vehic le lcmenr.ln d th e highway lement . l though hi s pol icy s pr imar i lv oncerned virhhighway character is t ics nd design. he psychor


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I fh e principle f full control f access s nvaluable s a means or preserving

I ,ite capacity f arterial ighways nd of minimizing accident otential, ut he

I pr.inciple oe s no r have universal pplication.Highways without control ofI access are essential as land service facilities, and the design features and

I oprating haracteristics fthese highways eed o be carefully lanned o ha tI thev will reduce onflicts nd minimize he nterference etween ehicles o hel ' .

I maximum extent nd still meet he needs f thehighway users.

I Speed s often a contributing actor n accidents, ut t must be related o

| .onditions. t is mproper o say hat an y given speed s safer han another or

I all combinations f the many kinds of drivers. vehicles, ighways, nd ocal

I .onditions. For a highway with particularly adverse oadway conditions,

l. . relatively ow speed may result n fewer accidents han a high speed, ut thisfact does not necessarily mean hat all potential accidents an be compensatedby low speeds. ikewise,vehicles raveling on good roads at relatively highspeed ma y have ower accident nvolvement ates han vehicles raveling attower speeds, ut t does not necessarily ollow that ye t a higher peed wouldbe even safer. he safest peed or an y highway depends n design eatures,road conditions. raffic volumes, weather onditions, oadside evelopment,spacing f intersecting oads, ross-traffic olumes, an d other actors. Acci-dents re not elated smuch o speed s o he ange n speeds rom he highestto the owest. Regardless f the average peed n a main rural highway, hegreater he dr ivers ' evia t ions ro m hi saverage pecd, i ther bove r below,th greater r e heir chances f being nvolved n accidents . hus . des ignt-eaturesha t educe he variance n speed fvchicles such s lat grades. pced- . f* ,nge

lanes , rade eparat ions , oo d signing nd ntarking) ontr ibute o hcsafe ty f he highway. ormal ly, cc idents nvolving chic les t h igh peed rcmore severe ha n hose t lo w speed'

Highways redesigned o be sat 'er br hc speeds ha t atisty he needs f rnostof th e drivers using he acility.Consideration n design houldbe given o thctype and haracteristics fthe drivers xpected o use he highway. rip purposcs(such s ecreation. ommuting o work.and hrough ravel) re actors ltcctingthe design o some extent. Allied with trip purposes re he vpes of vehiclcsI ikcly to use he highway. anging iom al l passenger ehic les o a highpercentage f heavv ommercial ehicles.Where ripsof one yp e predorninate.the acility ca n be designcd o tlt the specitic needs.

A study 26 ) on the ef 'fecr f the Interstate ighway System tn accidcntsshows a lower accident at e on tbur-llne dividcd highways ha n on tbur-llncundivided ighrvays. hi s ma y be seen n Tablc I-t],whrchwa s eveloped rotn

witvs wttnln lnterrfter pening cw scctions tf Interstate ighways o trlftlc.

., \h ighuay 'wi th rr tc 'd i ln -5 n )r m( ) r e n wit l thha s a vcrv t lw' incidcnccr. fhc: r r l - . r r ro l l i r ior t . - :ur \ ( ' r lv r, t l t ic l r ' s r t rss i t l t lhc r tc t l i : tn .' \ l t t ' t l i : tn" t l t l t

of up to 23 or 30 m is very desirable s a means f reducing ross-medianaccidents. he type as well as he width of the median or divided highwaysshould be given consideration. it h narrower medians, median barriers wille l iminate head-on ol l i s ions . ut a t the cost of some ncrease n same-direction accidents ecause ecovery space ha s been decreased. roperlydesigned median barriers minimize vehicle damage nd essen he accidentlikelihood f traffic moving n the same irection. narrow median lso doesnot allow for emergency eparture ro m th e ane.

Another tudy 27 ) elated ccidents o shoulder idth,alinement, nd gradean d ound hat ccident ates n sections it hcurves r grades ere much higherthan on evel angent ighway ections nd hat he ates were highest n roadshaving combinations f sharp curves and steep rades.

Accident Rates or Highways With AverageDaily Traffic Volumes

Type and Classof Highway

2.000 4,000Under to to2,000 3,999 7,999

8,000 16,000 32,000to to an d

15.999 31.999 Over

Before pening ectionof Interstate ystem

Four-lane ndividedFour-lane ivided

Alicr opcning ectionof Interst l te 1 'stem

Four-lane ndividcdFour-lanc ividcdIntcrst l te vstcnt

r-50

100 l -57

18 3 29 398 69

720 116I 7 l -529.5 65

196 24110 9 n56? 6.1

2t9_

wa y

Table l-8. Accident ates on four-lane ndivided nd four-lanedivided ighways eforeand fteropening ections fInterstate ystem n the same rafficcorridor.

This stud;- vhichwa s imitcd o two-lane ural oads. ends trong upport oth e postulate ha t straight, cvel ural oads withttut nterscctions r signiticlnttturnbcrs f pril 'ate riveways re he sat-est ighwlys within hcir eneral lass..fhc

ttrv accidcnts ha t occur on srraight evel ural oads without ntersectionsttnctwccn nc cl emcnt such s shoulder id th .Io r cr : t rnplc , nd accident a tcs s a l t r tos l er t ; r in o be c loudcd by randonlr . t r i l r t r o n s , f t h t ' c c i t l c n t p l l t t L ' r n .

AASEIQ 4e onet'ie De;tg,nafHi ghvayrond S ee sII:. U(,.V,(/l L o,ilt't)t.\ Un(l L nlenIi

I t l


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idents re ikely o occur where driversar e called on to make decisionsunder ircumstances here heirvehicles re unable o respond roperly s, orexample. where a ruck s descending grade. t would be ogical o expect moreaccidents n grades nd curves ha n on evel angent ighwayswhere ecisionsar e called or less requently nd vehicles re ully responsive. esign withtangent alinement an be overdone, owever. On extremely on g tangents,drivers have a tendency o completely elax. especially fter driving on a

congested ighway before entering a reeway. On some reeways here has beenconcem ver he number faccidents ha toccur when he driverapparently oe sto sleep. t is considered ighly desirable o provide genrle urvature nd avoida fixed cross section or long tangent ections. his can be handled by varyingthe median width, using ndependent oadway designs, nd aking advantage fthe enai n wherever easible. n addition, umble strips an be added o shouldersto reduce un-off-the-road ype accidents due to drivers falling asleep at thewheel.

With the mprovements n the elements f design or alinement, rade, andtraveled way, the general area of roadside design has become of increasingimportance. ccidents nvolving ingle ehicles unning ff the oad onstitutcmore han one-half of all fatal accidents n freeways.

When a vehicle eaves he oadway, he driverno onger as he ability o ullycontrol he vehicle. Any object n or near he path of the vehicle becomescontributing actor o the severity f the accident. he concept f the sat'cr rfbrgiving oadside hould no t be viewed as a by-product f the application fsafety riteria o each lement ut as a planned egment f the otal engineeringfor th e highway. Chapters an d 6 of reference 21 ) present n overview f thcAASHTO policy n this area, which is retlected hroughout hi s book n rhcgeometric esign riteria nd elements.

Basic o the concept f the fbrgiving oadside s the provision of a clcurrecovery rea. tudies ave ndicated ha t on high-speed ighways, relativclylevel raversable idth of 9 m from the edge of the raveled way permits about80 percent f the vehicles eaving he highway o be sat 'ely topped r retumcdto the oadwav. ven hough he 9 m is not a magic number nd he applicationof cngineering udgment s nccessary, hi s igure ha s been sed xtensivcly .sguide br recoverv ones. Within hi s area. wo major tems must be controllcdby th e designer: oadside lopes nd unyielding bstacles. NCHRP Report 17(28) discusses he effectiveness f clear recovery areas. The AASHTORtnd:;ide Design Guide (29) also discusses he effects slope and othcr log)-graphic -eatures ave on the eff'ectiveness f recovery areas. AASH'l'O recom-

- mends he tbllowing priority fo r treatment f roadside bstaclcs n existin

ii

. Remove he obstacle r redesi-qn t so t ca n be safely raversed.' Relocate he obstacle o a point where t is es s ikery o be struck.. Reduce mpacr everiry y usin,e n appropriate reakaway evice.' Redirect vehicle by shielding he obsracle it h a longitudinal raffic

banier and/or rash ushion.' Delineate he obstacle f th e above lternatives re no t appropriate.

Th e same riorities ouldbe bllowed n design, anicularly n upgrading ndrehabi itationprojects.

The design of guardrails nd barrier systems as become a subjecr ofconsiderable esearch. NCHRP Reporr JjO (30), and AASHTO,s RoadsitleDe.sigtt uide 129) ar e some of many published eporrs ha t deat with thissubject. of particular concern s the treatment of the en d section of th eguardrail r barrier.

Highway design engineers must ecognize he dynamic development ur -rcntlyunderway n th e enrire re a f roadside esign. lthough hi s publicationha s attempted o deal with th e subject n the most curent possiblemanner, heongoing esearch nd mplementation rojects illundoubtedlyoffernewerandbe tcr esults n he uture. Highwaydesign ngineers hould ndeavor o use henlost urrent cceptable nformation n their designs.

Conrmunication it h th e motorist s probably on e of the most complerproblcnrs f th e dcsign neineer; ne of th e best ools ha t he or sh e ha s br thisl)url)oscs he MUTCD (3), which depicts he national tandards eveloped brrr l l i r :n ing. ignal iza t ion.hannel iza t ic- rn ,nd marking br al l h ighways n th et l r r i tcr l ta tcs . hc nrain nressase f the MUTCD (3 ) is thc ' importance f'r r r r ii r r n r i n

l l ighrr r 'uscrs r c cpcndent n rafTic ontrol evices s igns , arkings . ndsrrrlills ir r ntirnrration,vaming. nd guidance. ogreat s he dependence ha tturrilirnn irrh-qualitv evices re necessArv br saf 'e. fficientus e an d publiclcccl)tlnccof an y hirhrvay egardless f it s excellence n rvidth. linemcnt. nc ts t ructur i l l c .s ign.

' \ t tr rl t ' t ' ic t 'rntrodcv cc should ave he bllow ns characrcristics:I) u ii l: r r rrn l l r l r lurr tL 'ed .l) cornrnand t tent ion. J) convev clear. implemeaning.I ' l )cr l rnrnrrndespectof oa d scrs . nd -5 ) iv eadequate im e brresponse . nrutklitrrlrr.tcviccs hu t ontrolor rcgulatc ratTic nusr e sanctioncd v law.

ljourbrrsic rinciples rc cmpltlved o cnsure ha t hesc equiremcnts re mct:t lcs i r : r t .luccrncnt .r r in tcnancc. nd ni t t l rmi ty. onsidera t ion hould eeivento thcsc rinciplcs f emplovment f tralfic control devices uring he lesisn

rccs an t o a m l n l m u mlllilt lro\c hi.ttrc ncccss.rry an be propcrlv placc,tl .

i l tc o1 ' rcnr t ionl t ' : r notor ehic le s a t i r l l - t i rnc .ccupat ion, ar t icul l r lv n' t ) l l l : r ' \ t ( ' ( l l r ( ' : l \ . . . \ i l r i r ' r. r s h t r r t l t l hc : r h l t ' f( ) ( ) n t . r : l l r 'hi s r r r h , . . r. , . h i r. l , , r r r r r

highways:

tlr lAASHTO--Eeomet.it Design of Highwavs and greets IIrl

Design eonh.ols and e+ircricr I 13


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rll tI t in imum tj is t racr ions . dvenis ing r other oacls ide i -sns hould or be placed II tvhere he y rvould nterf 'ere it h or confuse he meaning f standard r,affic II control devices. Advertising signs with bright colors or flashing ights ar e i| , , . II especially bjectionable n this espect. ights shining oward a driver ca n be

;

I bl inding. ar t ia l ly r fu l ly. for var ious er iods epending n individual ;i eI capability. right ights. n effect. an brm a curtain hiding what s ahead nd I

Ithus endanser motorists nd pedestrrans.

I n large umber f accidents n uralhighways ccurat ntersecrions. everal II studies av e ee n made at ntersections ith varying onditions, nd he esulrs II vary according o conditions tudied. actors o be considered re otal raffic I

volume, ercent f cross rafllc, urning movements. yp e of tratficcontrol, nd I1... . type of intersection. ncluding he design f the crossroad nd he utilization f II islands nd channelization n th e design. I

Various studies ndicate mprovements n safety ca n be accomplished yt

channelization f intersections, ntroduction f safety efuge slands nd side- lwalks or pedestrians, ighting, igning, nd raffic controldevices. hese av ebeen aken nto account n the development f this policy and esulting uidesfbr geometric esign.

A viable safety valuation nd mprovement rogram. s part of th e overallhighway mprovement rogram, s a necessity. he identificarion f safetyhazards, he evaluation f the eff 'ectiveness f alternative olutions. nd heprogramming f available unds or the most eff 'ective se s are of primaryimportance. he sat 'ety f the raveling ublic must be eflccred hroughout hchighway rograrn: n hc spot at 'ety rojects, n he ehabilitation rojects. n hc

- -construction of ne w highrvays. nd elsewhere. Ret'erence 2,1) providcs anumber f ntportllnt e'conttnendationsn saf 'cty s t re atcs o hc otal ighwayprogram.

ENVIRONiVIENT

A hirthrvay ecessarily as wide ranging flf 'ectseyond hlt of providing ral 'ficservice o users . t is esscnt ia l ha t he highway e considered s an elemcnt l'th c total environment. nvironment s used hcrein ret 'ers o thc torality ol 'humankind 's unoundings: ocia l . hys ic l l , a tura l . nd svnthct ic . r ncludcshunran, lilnt. and nimal communities nd hc orccs hat ac t on ll thrcc. 'fhchighway an and hould e ocated nd designcd ocomplemcnr ts environmcnl

Thc rcl surrounding proposetl ighwa-vs an nterrclated vstcrn l 'nltuntl.synthct ic , : tn t l ociolouic r r r i lb les . hangcs n one vur iahlc i th in hi s vs tcrnctnn() l rc t t l t t lc r t l r t lu t ontc l ' l i .c t n r t ther ar iahlcs . onrc t t ' thcsc onsc-

quences ay be negligible, ut othersma y have trong nd asting mpact n heenvironment . ncluding he sustenance nd qual i ty of human ife . Becausehighway ocation nddesign ecisions av e an effecton adjacent rea evelop-ments. t is mportant ha t environmental ariables e given ul l consideration.Care should be exercised o insure hat applicable ocal. state and federalenvironmental equirements re met.

ECONOMIC ANALYSIS

Highway economics s concerned ith he cost of a proposed mprovement ndthe general benefits esulting rom it. Proposed mprovements hould be ana-lyzed in accordance ith AASHTO's A Manual on User Benefit Anal,-sis fHighv,av and Bus-Transit mprovements 31).

REFERENCES

L Pilkington.G. B. and P. D. Howell. "A Simplified Procedure or

Computing Vehicle Offtrackingon Curves." FHWA RD-74-8, De -cember 983.

2. Alexander. G. FL and H. Lunenfeld. A User's Guide To PositiveGuidance 3r d Edition). Washington, D. C.: U. S. Department fTransportation, ederalHighway Administration, 990.

-1. U. S. Department f Transportation, ederal ighway Administration.iVlunual n UniJot'mTrffic Control Devir:esJltr treets nd H ghu'ut's.Washington. . C. : U. S. Government r in t ingOff ice . 1988.

4 . Johannson. . lnd K. Rumar. Driver ' s Brake React ion ime."l - lurnan actors , ol . 13 . No. I ( 191 ) :22-21

5. Fell. J. C. "A Motor Vehicle Accident Causal System. he HunlanElement." eport No .DOT-HS-80 -2lJ. Washington. . C.: National

Highrvrv raff icSafety dminis t ra t ion.ul y

1974.6 . Schmidt . an d P . D. Connol ly. Visual Considera t ions f lv lan. hcVt-'hiclc nd the Highwavs." SP-279-SAE. ew York: Socien' ot, \u tomot ive ngineers , 966.

1 . Ti l lcy. D. H. , C. W. Erwin. an d D. T. Gianturco. Drowsiness ndDriving: Preliminary Report of a Population Survey"' Papcr \ ' t , '7 - j0 2 -S, lE. ew York: Socie tv f Automotive ngineers . 973.

Design and Operations." eytrt No . FHWA-TO-,Y6-/,Washington.D. C. : Lr. S . Depar tment f Transpor ta t ion. ederal ighrvav dmin-is tn l t i ( )n .hv I986.

AASHTO-Ceoqlll!:4' DejtC! gf HtSl!t!!\s and Streets Design Controls nd Criteria


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L .

I l.

1 9 .

10 .

I t .

2) .: - 1 .

30.

3 1 .

) : .

J J .

34 .

3 5 .

r6 .

31

1 6 .

q. Aater, B . an d H. Lunenf 'e ld . 'Three Bearn Headl ieht vaiuat ion."Report No. HS-238-2-4 I -LInstitute of Traffic Engineers. reev'ut ' Operations. Washington.D. C. : ns t i tu te f Traff lcEngineers . 96 .Transportation Research Board. Highn'av Cuput'itt' Munual. SpeciulRcport No.209. Washington. . C.: Transportation esearch oard.1985 Rev i sed 994 ) .

Fee . u l ie Anna et a l . ln ters ta te ys tem ccident esearch tudy1. "Washington. D. C.: U. S. Department f ' Transportation, ederalHighway Administration, ctober 1970.Glennon. J. C.. J. J. Valenta. B. A. Thorson. and i. A. Azzeh.Tec'hnical Guidelines or the Control oJ' Direct Ac'c'ess o ArteriulHighv,u-vs. olumes I and 2. Kansas City, MO: Midwest ResearchInst i tu te , ugust 1975.

14 . Maring,G. E. "Pedestrian ravel Characteristics." ighv'ayResearclrRecord 406. 1972: 14 20 .

| 5. Cameron. R. M. "Mechanical Measurement f Pedestrian olumes."TR B 498. 1971: 13 19.Fruin, .J. Pedestrian Iunning, nd Design. Metropolitan ssociation

of Urban Designers nd Environmental lanners. nc., 197Older, S. J. "Moventent of Peclestrians n Footways n ShoppingStreets." ' trulfic ttgineering nd Control August 1963: 16 0 163..

Fruin . . J. Designing or Pedest r ians : Level-of-Service oncept ."l /RBJ -5 -5 . a sh ing ton , .C . . 97 l : l - 15 .Di Pie t ro , C. lv l . ancl L. E . King. "Pet les t r ian ap-Acceptancc."t lR I I 108 .Wash in s ton . .C . . 1970 : 0 -9 l .AASHTO. Guitle 'o I) e e opnte t ' B cv c c I'- c ' .s.Washingtort.D . C . : A A S H T O . 9 9 lAASHTO. Itighwol' Dcsi.q,n nd Operutiortul Prut ' t i te Relotcd ttIl i ghvrttt ' .Sqli ' tr ' .ashington. . C.: AASl-11-O. 97+.1976,At' ' t ' idant dcts.Washington. . C.: Nltionill Sat'ety ouncil., , \r\SllTO et al. "Enhlncing F{ighrvay atcty n an Err of LinritcdRcsourccs." \ rcport csulting 'rotn sytnposiunt onductcd .. '"hcTransportation csearch oard. Novembcr 9lJ ." ln ters ta tc ls tcnrAccidcnt esearch." c tober 970.Darr. O.K. . J r. and L. iVlann. r. "Rcla t ionship f Rurul HighwryGcornctrv o AccidcntRltcs n Lt'tuisiana."li ,qhxut Rtscttt ' t R(t ' , tr, t

21 Bi l l ion.C.E. an d W. R. Stohner. A Detai led tudyof Accidents sRela ted o Highway houlders n New York State ."Proc ' . RB 1951 :491.

28. Graham. . L. "Effectiveness f Clear Recovery Zones." NCHRPReporr 17 1982t .

29. AASHTO. Roadside Design Guide. Washington, D. C.: AASHTO.r989.

R o s s . H . 8 . . D . L . S i ck ing , R . A . Z i m m e r , and J . D . Mich i e ."Recommended rocedures or Th e Safety er tbrmance valuat ionoi Highway Features ." CHRP Report 50 (1993) .AASHTO. A Manual on User Benefit Analysis J'Highu,at' nd B us-Transit mprovements. ashington, . C. : AASHTO. 1977.Olson, P. L.. D. E. Cleveland, P. S. Fancher, . P. Kostynuik, an dL. W. Schneider. Parameters t 'fectingStopping Sight Distance."NCHRP Report 270, (1984). Developed y New York DOT. fromreport).Koepke, . J. , an d H. S. Levinson. Access Management u idel inesfor Activity Centers." CHRP Report 34 8 (1992)."Human Factors nd Safety Research elated o Highway Design ndOperations." ransportation Re.search e


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Ctrapter IIELEMENTSOF DESIGN

SIGHT DISTANCE

General Considerations

The ability to see ahead s of the utmost mportance n the safe and efficient

operation f a vehicle on a highway. On a railroad, rains are confined o a ixed

path, yet a block signal system and trained oprators are necessary or safe

operation. On the other hand, he path and speed f motor vehicles n highwaysand streets are subject o the control of drivers whose ability, training, and

experience re quite varied. For safety on highways he designer must provide

sight distance f sufficient ength hat drivers can control he operation f their

vehicles o avoid strikingan unexpected bject on the raveled way. Certaintwo-lane ighways hould ls o ave ufficient ightdistance o enable rivers o

occupv he opposing raffic an e or passing vertaken ehicles vithout isk of

lccident. wo-lane ural highways hould'generally rovide uch assing ight

distance r frequent ntervals an d fo r substantial ortions of their length.

Conversely. r normally s o f little practical alue o provide passing ight

distance n wo-lane rban treets r arterials. he ength nd nterval f passing

sightdistance hould e compatible with th e criteria stablished n the chapterpcrtaining o that specific ighway or stteet lassification'

Sight disrance s discussed n ibur steps: l) the distances equired or

sropping. pplicable n al l highways: 2) he distances equired or th e passing

of overtaken ehicles. pplicable nl y on two-lane ighways: 3) he distances

nccded br clecisions t cornplexocations: nd ('l) th c criteria or measuring

thcse istances ir rus e n ctciign. he design f linement ancl rotile o provide

thcse istances nd to meet hcse riteria rc described ater n this chapter. he

spccill conditions ellted o sight ciistances rt ntersections re discussed n

Chaoter X.

Distance

Si11ht istance s he cngth f roaclwayhead visible o hc drivc'r. hc minimumsisht listencc.vlilable tt n :t rtlatirvlvshould bc 'suftlcicntlv ong t ' l enable

AASH 7lO.=4e on et c Desjgn of lli S1w y!q4;t eet; ElemeLLspf Qt;ign t 1 9II1I


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vehicle raveling tor near he design peed o stop before eaching stationary

objeqt n it s path. Although greater ength s desirable, ightdistance t every

point along the highway should be at |east hat required or a below-average

operator r vehicle o stop n this distance.Stopping ightdistance s he su m of two distances: he distance raversed y

th e vehicle ro m he nstant he driversights n object necessitating stop o he

instant he brakes are applied and he distance equired o stop he vehicle rom

the instant brake application begins. These are referred o as brake reactiondistance nd braking istance, espectively'

Brake Reaction Time

Brake eaction ime s the nterval between he nstant hat he driver recognizes

the existence f an object or hazard n the oadway ahead nd he nstant hat he

driver actually applies he brakes. This interval ncludes he time required o

make he decision hat a stop s necessary. nder certain conditions, such as

emergency onditions enoted y flares or flashing ights, operators ccomplishthese asks almost nstantly. Under most other conditions he operator must

subconsciously ssociate he object ahead with stationary bjects djacent o heroadway, uc h as rvalls, ences, rees, oles, or bridges, o determine hat he

object s also stationary r moving at a slow speed. hese determinations ak e

time, he amount f which varies onsiderably epending n he distance o he

bUject. he acuity f he operator, he natural apiditywith which he driver eacts,

rnospheric isibility. he yp e and he condition f the oadway, nd he ype,color, an d condition f th e hazard. ehicle peed nd he oadway nvironmentprobably lso ntluence eaction ime. Normally, an operator raveling t or near

th e design peed s rnore lert ha n one raveling t a les.ser peed. n operator

on an urban acility confronted y innumerable ossibilities or conflicts ro m

parked ehicles. riveways, nd cross treets s also ikely o be more alert han

th e same perator n a limited-access acilitywhere uch conditions hould e

alrnost onexlstent.The study l) rct 'erred o in Chapter I wa s based n data ro m 32 1 driverswno expected o apply heir brakes. he median eaction-time alue br these

dr ivcrs wa s 0.66 s rvi th 0 percent equir ing 1. 5 s or longer. hese indings

corre la te it h rhose f ear l ier tudies n which aler ted r iverswere also sed.

Anorhcr tu t ly 2) gives .6 .1 as he average alue: 5 ercent f the dr iversrcquirc t l ver s. n a th i rd s tudy 3) react ion- l ime alues anged rom 0. '1 o

l) . when he s icnal wa.s nexpected.thc lrivcrs' rcsp()nscs cre ound o increase y approximately s or longer:

sotne cact ion i t t tcs e ing 1. 5 s or more . This ncrease ubstant ia ted ar l ier

laboralor l nd roat l cs ts n which he onclus ion as rawn ha t he r iver wh o

required .2 to 0. 3 s under aler t ondi t ions equired 1. 5 s under normal

condi t ions .Minimum eaction imes hu s ouldbe at east 64 ;0.64 or alerted rivers

plus s or th e unexpected ignal. ecause he studies se d imple rearranged

signals. he y represent he east omplex of roadway onditions. ve n under

these imple onditions r wa s ound ha t some perators ay ak e over 3'5 s o

respond. ecause ctual onditions n he highway re generallymore omplex

than hose f th e studies nd because here s widediversity n he eaction imesrequired, t is evident hat he value adopted houldbe greater han 1.64 . n

determinafion fsight istance or design, he eaction im e should e arger ha n

the average or all drivers under normal conditions. t should be arge enough o

include he reaction ime required br nearly al l drivers under most highway

conditions. For approximately 90 percent of the drivers in the first study

mentioned. reaction ime of 2.5 s was ound o be adequate. reaction ime of

2. 5 s has hu s been ssumed n the development f Table II-1.A reaction im e of 2.5 s s considered dequate or more complex onditions

than hose f th e various tudies, ut it is not adequate or th e most complex

conditions ncountered y the driver. Additional consideration f the most

complex onditions uch s hose ound at multiphase t-grade ntersections nd

ramp ermini t hrough oadways an be ound ater nhi schapter n he section

"Decis ion ightDis tance ."

Braking Distance

Thc appror imiUe ruking is iancc l 1vchic lc on lt lcvcl r t la t i rv lv ra l 'be

detennined y thc use of the standard brmula:

whcre: dv

I

t t =V t

1 < l + -L J + I

- br lk ing dis tancc . := ini t i l lspced. m/h: an d= coctficicnt f frictionbetwecn ircs an d oldrvlr

In this brrnula i l r br lk ing dis tance hc f f lc tor s uscd s l l t t lvcr l l lor 3

s ingle alue hat s cpr tse t l tx t ivebr he wholcof the pccd hlngc. Nlcasure '

ments horv hat is not hc same or all spcct.ls.t decrcascs s hc nitial specd

l nCfe aSCS . lI tv

pressure f t i res . ornpt ts i t ion t ' t i res , i rc rcad at tcrn nd epth l f t re ld , l pe

ant l Condi t i t ln , r f lt e pl tvL ' l l lenfur l 'ace . nt l lt c prcscncc l ' t t t t r i s turc , tud.

I

46UIa4cpuctte P e;at pfAs!!!q and Street Elements f Design 12 1

a policy on geometric highway

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