barandas segun aashto

A SUPPLEMENT TO

A GUIDE FOR SELECTING, DESIGNING AND LOCATING T R A F F I C BARRIERS

PREPARED BY

THE TEXAS TRANSPORTATION I N S T I T U T E

MARCH, 1980

i

TABLE OF CONTENTS

UNIT -

1

MATERIAL TITLE

Correct ions To The AASHTO Guide For Se lec t ing , Loca t ing and Designing T r a f f i c B a r r i e r s (1977) Suggested Design Curve f o r Roadside Di tches

Impact Behavior o f B a r r i e r s on Non-Level T e r r a i n

Table o f NHTSA Accident Costs

Revised - A Cost -Ef fect iveness Se lec t i on Procedure For B a r r i e r s

Federal B u l l e t i n on Min i -S ized Cars

Crash Cushion Design Curves

Suggested Roadside B a r r i e r F1 a re Design (S ta te o f Iowa) Sample Graphic Sol u t i o n t o The Length-Of -Need Equat ion

Suggested 70 mph Clear Zone Width For Various Side Slopes

Tables o f Clear Zone Width Increase on Hor izon ta l Curves

Guide l ines For Determining Guardra i l Need, Loca t ion And Standards - Georgia

iii

OORRECT IONS JANUARY 1980

AASHTO GUIDE FOR SELECTING, LOCATING, AND DESIGNING W F I C BARRIERS (1977)

Page 16 - Dimension "CZ," should read " A C Z ~ " .

Page 17 - Change : L R ~ O "ACZ, = R(1-COS rn) ( s l ide slope-0 .l o r f l a t t e r ) To: ". . . [side slope = -0.1 o r f l a t t e r ] .

Comment: Words i n brackets a r e not p a r t of f o n u l a .

Page 29 - Section E-E: Change "60'" t o "30'"

Section A-A: Change "40 "' t o "20"'

Page 49 - Last l i n e i n 3rd f u l l paragraph, change "Section 111-B-3 and 111-B-4" To: "Section 111-E-3 and 111-E-4"

Page 52 - Next t o l a s t paragraph, change "No" t o "Three".

Page 61 - Change " . . .posi t ive i f sloping downward" To: "...negative i f s loping downward."

Page 64 - Change heading : "Shyline o f f s e t ( f t ) " To: "Shyline o f f s e t , LS ( f t )" Qlange ins t ruc t ions under l e f t s ide of t a b l e t o read "*when Ly0.5Ls, Lt s h a l l have a..."

Page 4 - In the f i r s t l i n e of the last paragraph change "Underlined" t o "I tal ized" and "Appendix I" t o "Appendix J".

Page 105 - In the l a s t 1 ine of the seventh paragraph change reference (145) t o (57).

Page 317 - In reference 57 change 1975 t o 1976 and add: (Report No. 's RIhTA-RD-77-3 and 4 ) .

Pages 294 6 322 - Change the l a s t reference under 1976 and 1977 an

page 294 and reference 145 an page 322 t o read, "blodified Breakaway Cable Terminals f o r Guardrails and Median Barriers ," N W Research Results Digest No. 102, May, 1978.

Page 37 - Line 3 of the descr ip t ion o f G 3 should read, "6" .x 6" x 0.188" s t e e l tube."

1

SUGGESTED DESIGN CURVE FOR ROADS I DE DITCHES

This graph i s a composite o f F igure 111-A-7 , 111 -A -8 and 111 -A -9 i n the B a r r i e r Guide. The composite graph e l im ina tes a g rea t deal of the confusion associated w i t h the i n t e r p r e t a t i o n o f the d i t ch design c r i t e r i a presented i n the guide.

FRONT SLOPE al :a l

BACK SLOPE a2:a 2

IMPACT BEHAVIOR OF BARRIERS ON NONLEVEL TERRAINS

BY HAYES E . ROSS, JR., AND DARRELL G. SMITH

TEXAS TRANSPORTATION I N S T I T U T E TEXAS A & M UNIVERSITY

C o p y o f a p a p e r p r e s e n t e d a t t h e N a t i o n a l ASCE M e e t i n g , A t l a n t a G e o r g i a O c t o b e r 2 3 - 2 5 , 1979. ASCE PREPRINT No. 3 6 3 4

ABSTRACT

IMPACT BEHAVIOR OF BARRIERS ON NONLEVEL TERRAIN

Hayes E. Ross, Jr., and Darrell G. Smith

Six full-scale crash tests were conducted to evaluate the impact behavior

o f two widely used roadside barriers when placed on a 6:1 side slope. Four of

the six tests involved a standard W-beam rail on metal posts (G4(1S) system) and the other two tests involved a three-cable barrier mounted on metal posts (GI systern). The tests were conducted and evaluated i n accordance w i t h national guide1 i nes for testing of roadside appurtenances.

Based on the resul ts, i t i s recommended that the G4(1S) system not be placed on 6: 1 or steeper side slopes. Placement of the G 1 system on a 6:l

side slop2 i s accsptable provided ample space exists between the barrier and the hazard i t i s shielding.

KEY WORDS: Automobi 1 es, Highways, Nonl eve1 Terrain, Safety, Slopes, Tests,

Traffic Barriers

IMPACT BEHAVIOR OF BARRIERS ON NONLEVEL TERRAIN

Hayes E. Ross, J . , M , ASCE, and Darrell G . Smith 2

INTRODUCTION AND SCOPE

Impact behavior of a roadside or median barrier i s dependent on a number

of factors, including s ize and spacing of posts, size and mounting height of

r a i l o r beam, offset of beam from posts, soil conditions, and roadside condi- v

tions between the edge of the traveled way and the barrier. L i t t l e i s known

about the effects of the l a t t e r factor although i t may have the greatest i n -

fluence on performance. In general, barriers have been designed and tested for

f l a t terrain conditions even though roadside and median barriers are commonly

placed on side slopes, in depressed medians, in ditch bottoms, etc.

A t tftc i nzep t i~n o f th i s study t r ip s were made to several s ta tes to survey

current bsrriey pl acc:!iefi t practices and to sol ic i t i n p u t from various s tate

transportatiou perso!lr,el. I t was found t h a t there are four basic conditions

for which t,oadside i1n3 median barriers are typically placed on nonlevel terrain.

These are i l lustrated i t ] the photographs of Figures 1 through 4. F i rs t , bar-

r i e r s userj t o shield bridge piers, overhead sign bridge supports, o r other rigid objects in depressed medians or on side slopes are often placed as near to the object as t he barrier design permits. In many cases t h i s places the barrier on the side slope as shown i n Figure 1. Secondly, barriers used to

shield bridge abutn:ents ,or other rigid objects near the shoulder are often flared away from the shoulder and terminated. As a consequence a portion of

the barrier i s placed on the side slope as i l lustrated i n Figure 2. Thirdly,

'~esearch Engineer and Professor, TTI , Texas A&M University, Col lege Station, Texas. '~esearch Associate, TTI , Texas A&M University, College Station, Texas.

Figure 1. Barr iers shielding r i g i d objects

Figure 3. B a r r i e r on barn r oo f sect ion

8

Figure 4 . Median barriers.

9

roadside barriers are sometimes placed on "barn roof" sections i n high-fill

areas. Typically the roadside i s composed of a shoulder, then a relatively f l a t

sloped embankment (usually a 6:l slope) which may extend u p t o 20 f t (6.1 m) la te ra l ly and f inal ly a relatively steep embankment (usually 2:l o r steeper). In this case the barrier is placed on the 6:l slope to shield the steeper em-

bankment. This is i l lustrated i n Figure 3. The l a s t condition, which is not

as comnon as the other conditions mentioned, involves median barriers used to

prevent cross-over head-on accidents that are placed on stepped o r depressed

medians. This i s i l lustrated i n Figure 4. To gain insight on behavior o f typical barriers on nonlevel terrain, two

roadside barriers were evaluated through a fu1 l-scal e crash test program.

These were the ~1~ system and the 6 4 ( 1 ~ ) ~ system. The GI system consists of three steel ,:ables mour~ted on "weak" posts while the G4(1S) system consists of a standard s t:ecl !,f-bflal~ rilolrnted on "strong" posts. Selection of these systems

was based CR few f ; : c r rs : ( a ) both are operational (as per Reference 1) ; (b) b o t h are ~ i d e l y used; (c ) both are used to varying degrees on nonlevel terrain conditiol:~; and go considerable la teral movement on impact while the G4(1S) barrier i s a "semi- rigid" system and \$il l displace much less than the G 1 system for a given se t of impact conditions.

Selection of a 6:1 slope was based on an evaluation of previous research

involving computer s i ~ u l ~ t i o k of vehicle trajectory on side slopes (Appendix F of Reference 4). The reference: work showed that a vehicle could possibly vault a typical roadside barrier placed near the shoulder on slopes steeper than

approximately 10:l . to 8:l. I t has concluded that a 6:l slope would be i n the

a~es ignat ions are consistent w i t h those contained i n Reference 4.

c r i t i ca l range for lateral barrier offsets up to approximately 12 f t (3.66 m) from the edge of the shoulder.

This paper was condensed from a report to the Federal Highway Administra-

tion [6]. TEST CONDITIONS AND EVALUATION CRITERIA

Test Site. The t e s t s i t e , shown in Figure 5, was designed to represent a

common roadside section defined by the road surface i t s e l f , a shoulder, a side

slope, and a back slope. The road surface consisted of an existing concrete b

surface (airport apron). An 8 f t (2.4 m) shoulder area was cut on a 15:1 slope, and a i 2 f t ( 3 . 7 m ) side slope was cut on a 6:1 slope. A 3 t o 4 f t (0.9 t o 1.2 m ) ditch bottorn was added to aid i n drainage and a 4:1 back slope re- turned the confi~urat ion to the original ground level. The existing horizontal

concrste surface has a dowi~grade slope parallel to the r a i l of 1% and the t e s t

slopes w r e cozstructed t o parallel t h i s drainage pattern.

Le,;~-jth of the -ir,std! 12d roadside barrier was 200 f t (61.0 m ) i n each case excludin; the rigid snchors on both ends. Two sets of anchor foundations were

instal led, orte locztjng it!e face of the guardrail 6 f t (1.8 m ) from the edge of the sF,olilCer (inst?.llation A ) and the other locating i t 12 f t (3.7 m) from the shoulder ( ins ta i la ticn B ) .

Description o f -- Garrier Systems. Reference should be made to Figure 6 for

de ta i l s of the t w 3 b?rr ier systems described below.

M(iS) B'Loc::ed-?~5 h ' - B ~ a n . This system consisted of a standard 1 2 gauge - - -. - - - -

steel W-beam mo~rnted on W6 x 8.5 steel posts. The blockout was a W6 x 8.5,

14 in. (35.6 cm) long steel block which was bolted to the steel post. The top of the r a i l was 27 in. (68.6 cm) above ground level a t the post. The posts were spaced 6.25 f t (1.91 rn) center t o center, and they were se t 42 i n . (106.7 cm) i n a n 78 in. (45.7 cm) diameter dr i l led hole and then backfilled with a well graded base material. This roadside barrier system, which was used i n t e s t s 1

ROADWAY : HORIZONTAL CONCRETE SURFACE

ORIGINAL BACKSLOPE

METRl C CONVERSIONS: Ift. = 0.305m

Cross Sectional View

l sometric View

(b)

Figure 5. Test s i t e geometry.

through 4, i s shown i n Figure 7.

G I Cable Guardra3Z. This system consisted o f three 3/4 in. (1.9 cm) d ia- meter pretensioned cables mounted on S3 x 5.7 steel posts. The top cable was

30 in. (76.2 cm) from ground level , and the cables were spaced 3 in . (7.6 cm) apart. The cables were attached t o the steel posts by 5/16 in . (0.79 cm) d ia- meter steel hook bolts. A 1/4 in. x 8 in . x 24 in. (.64 cm x 20.3 cm x, 61.0 cm) steel bearing p l a te was welded t o the back flange o f each post. The posts were

spaced 16 ft (4.9 m) apart center t o center, and they were dr iven 29.5 in . (74.5 cm) i n t o the so i l .

Cables were attached t o the downstream end anchor by turn-buckles, and the

upstream end o f each cable was attached t o a spring compensating device. The

cables were pretensioned t o approximately 1000 1 bs (454 kg) before the test . This system, which was used i n tes ts 5 and 6, i s shown i n Figure 8.

Eva1 uat ion Cr i te r ia . Reference 5 states tha t three apprai sal factors are --

to be considctred For t e s t o f a long i tud ina l barr ier : (a) s t ruc tu ra l adequacy, (b) impact severi ty, and (c) vehic le t ra jec to ry hazard. I n summary, c r i t e r i a f o r each appraisal fac to r are:

(a) StructuraZ ~ d ~ q v a o y - The t e s t art ic le shuZZ redirect the vehicle; hence, thg vehicle shuZZ not penetrate or vault over the ins ta lk -

tion.

(b ) Impact Severity - Where the t e s t art ic le fwlctwns by redirecting the vehicle, the maximum vehicle accelemtwn (50 ms avg) measured n m the center of mass shouZd be less than the following values:

Mzzimwn Vehhle Accelerations (g ' s ) Luterat LongitudinaZ Tota l Remarks

3 5 6 Preferred 5 10 12 Acceptable

Figure 7 . G4(1S) barrier installed on 6 : l slope.

15

Figure 8. G1 cable rail installed on 6:l slope.

%se r i g i d body acceteratwns appZy t o impact tes ts a t 25O

or less.

(cl VehicZe h.ajectory Hazard - After impact, the vehicle trajectory rmd f h Z stopping position shaZZ intrude a minimum distance in-b

adjacent t r a f f i c Irmes. Two t e s t s a re recommended [5] t o evaluate a roadside barrier along i t s

"length of need" (excludes end treatments). A strength t e s t i n which the barrier i s impacted a t 60 mph (96.5 km/h) by a 4500 l b (2043 kg) vehicle en-

\

croaching a t 25' i s recommended. The primary purpose of th is t e s t i s to eval-

uate the struc.tura2 adequacy of the barrier. The second t e s t involves a 60 mph

(96.5 k m l h j impact by a 2250 1b (1022 kg) vehicle encroaching a t 15'. This t e s t is designed primarily to evaluate the impact severi ty of the barrier.

Vehicle damage was assessed a f t e r each t e s t in accordance with two nation-

al rating sca,l es, narcly TAD [7] and SAE [2] . TEST RESL!i.TS --

Shown i n Table 1 i s a summary of the six crash t e s t s and results obtained

therefrom.

Test 1. This was a stmscturai! adequacy t e s t of the G4(1S) system for a 6 f t (1.8 m) offset . Upon impact the lower part of the bumper just cleared the top of the r a i l a ~ d the car vaulted over the r a i l w i t h 1 i t t l e redirection.

Test 2. Test 2 was a nonstandard t e s t b u t was conducted for two primary

reasons: (1) to determine i f the barrier was structurally adequate for a lower encroachment angle (i5' versus 25'); and (2) to provide data for validating and updating barrier computer simulation programs ( to be used 1 ater to supplement the crash t e s t program). The car was contained and smoothly redirected. However, the car would have crossed adjacent t r a f f i c lanes thereby posing a potential trajectory hazard.

Table 1. Zurnnlilry o f crash t e s t r e s u l t s a

ADHERENCE TO PERFORMANCE

TEST NO.

BARRiER TYPE

BARRIER OFFSET (ftP

VEHICLE WE I GHT

(1 t i ----

IYFACT SPEED ( m ~ h j L

IMPACT ANGLE 0

SPECI FI CATIONS~ STRUCTURAL IMPACT EXIT ADEQUACY? SEVERITY? ANGLE?

NO^ N/A d Yes Yes NO^ of N/A f Yes Yes NO^ Yes N/A Yes Yes Yes Yes

"11 b a r r i e r s tested were placed on a 6:l side slope. b ~ i s t a n c e from outer edge o f shoulder t o face o f b a r r i e r . 'see Sect ion V-A fo r d iscussion o f performance spec i f i ca t ions . dyehi c l e vaul ted over b a r r i e r . e ~ u b j e c t i v e evaluation. f ~ e h i c l e penetrated through f rac tu red r a i l element. Met r ic Conversions:

N/A - Not Applicable.

Test 3. This was a structuraZ adequacy t e s t of the G4(1S) system for a 12 f t (3.7 m) offset. Upon impact the vehicle began to redirect. However, the combined action of la te ra l , longitudinal , and vertical loads on the r a i l and

r ight front wheel snagging on support posts resulted i n a complete fracture of

the r a i l . The r ight front wheel and portions of the wheel assembly were torn

f ree of the vehicle. The vehicle penetrated the r a i l and came to res t approxi-

mately 90 f t (27.5 m) beyond the point of impact jus t behind the barrier. I t is noted that post and r a i l material properties were i n compliance w i t h recom-

L

mended standards.

Test 4. This was an Gpact severity t e s t of the G4(1S) system for a 12 f t (3.7 m) offset. The car was contained and smoothly redirected. However, the car would have crossed adjacent t r a f f i c lanes thereby posing a potential t ra - jectory hazard.

Test 5. This was a scrueturai! adequacy t e s t o f the G1 system for a 6 f t (1.8 m) offset. The ccr was contained and smoothly redirected and there was no trajectory hazard. Maximum dynamic deflection of the cables was 9.5 f t (2.9 m).

Test 6. This was cn impact sezlerity t e s t of the GI system for a 6 f t

(1.8 m) offset . The czr was contained and smoothly redirected, decelerations were below suggested l imits, and there was no trajectory hazard. Maximum dynamic deflection of the cables was 4.2 f t (1.3 n ) . CONCLUSIONS

Conclusions drawn as a resu l t of the s ix t e s t s reported herein are:

(1) The G4(1S) roadside barrier system does not sat isfy structuraZ adequacy requirements when placed on a 6:1 slope a t offsets up

through 12 f t (3.7 m). In other words, the barrier, when placed a s stated, will not contain and redirect a 4500 I b (2043 kg)

automobile impacting a t 60 mph (96.5 h / h ) and an encroachment angle of 25'.

(2) The G4(1S) system, when placed on a 6:1 slope and a 6 f t (1.8 m) offset , will contain and smoothly redirect a 4500 1 b (2043 kg) automobile impacting a t 60 mph and an encroachment angle o f 15'.

A1 though not proven by the t e s t , i t is the authors' opinion tha t

the G4(1S) system will sa t i s fy impact severi ty requirements when placed on a 6:l slope and a 6 f t (1.8 m) offset.

( 3 ) The G4( 1s) system sa t i s f ies impact severity requirements when placed on a 6:1 slope a t a 12 f t (3.7 m) offset. In other words, the barrier, when placed as stated, will contain and smoothly

redirect a 2250 lb (1022 kg) automobile w i t h tolerable decelerations when impacting a t 60 rnph (96.5 km/h) and an encroachment angle of 15'.

(4 ) Post-impact vehicle trajectory was 1 ess than desirable fol lowing the G4(1S) tes t s in which the vehicle was redirected ( t e s t s 2 and 4 ) . Results cf these two t e s t s could be interpreted t o mean that a vch.icZs ,trajectory hazard existed, i.e., a f t e r impact, trajectory of the vehicle would pose a hazard t o t r a f f i c in adjacent lanes.

( 5 ) T h 3 G l roadside barrier system, when placed on a 6:1 slope a t a 6 f t (1.8 m) offset, sat isf ied a l l performance specifications for a roadside barrier, i . e. , structwlaZ adequacy, impact severity,

and 7)ehicZe trajectory hazard. When compared to the G4(1S) system, improved performance of the GI system i s attributed to the

30 i n . (76.2 cm) mounting height of the top cable (versus 27 i n . (68.6 cm) for the W-beam), The cables remained a t essentially the

same height following impact while the W-beam in the G4(1S) system rotated backward and downward, creating a ramp for the vehicle.

RECO!,!MENDATI ONS

Results of limited t e s t s reported herein form a basis for the tentative

recomnendations which follow.

(1 ) Roadside or median barriers u t i l izing the standard W-beam, mounted 27 in. (68.6 cm) above ground, should n o t be placed on 6:1 or steeper slopes for offsets up t o 12 f t (3.7 m ) . Offset i s the la teral distance from the shoulder's edge to the face of the bar-

r i e r . When placed within these boundaries the barrier cannot be

expected t o contain a n d redirect an automobile leaving the shoulder

a t 60 mph (96.5 kin/h) with an encroachment angle equalling or ex- r s ~ d i n g 25'. I n other words, the barrier will not meet current

psrformlnce spl?: i f i cations regarding "structural adequacy" [5].

E.rr,ier pa~fc,ci;?rce for offsets greater than 12 f t (3.7 m) i s un - known as.d ti-!$r+ifore no reconmendation can be made regarding place- men t bl-t,y~nc: t . : ' s distance. Trajectory analysis [4] indicates an errant autcncrl:'lle kith the above encroachment conditions would

strf ke t t i h bar:-ier a t or below the normal or level terrain impact

height for offsets greater than 12 f t ( 3 . 7 m ) . I t must be noted that the G4(iS) system - did contain and redirect an automobile a t

6 f t (1.8 K) 2nd 12 f t ( 3 . 7 m) offsets for a 60 mph (96.5 k m / h ) , 15' encroachir~a-it angle. S ta t i s t ics have shown that approximately

8 0 b f a11 errant vehicles leave the travel way a t an angle of 15'

or less. Barrier systems now in place on 6:l slopes ut i l iz ing a

27 i n . (68.6 cm) W-beam can thus be expected tob contain and redirect a l ~ r g e majority of errant vehicles.

(2 ) The GI roadside barr ier system i s acceptable fo r placement on s ide slopes 6:1 o r f l a t t e r . However, care mus t be exercised in its placement t o insure an adequate distance behind the barr ier f o r

displacement during impact. A 1 atera l displacement of approxi-

mately 10 f t (3.1 m) can be expected i f the bar r ie r i s impacted by a fu l l -size ca r traveling a t 60 mph (96.5 h / h ) encroaching a t 25'. Hence, the barr ier should be placed 10 f t (3.1 m) o r more l a t e r a l l y from r ig id objects. Tests [3] have shown the G 1 system will con- t a in and red i rec t an automobile when placed approximately 18 i n .

(45.7 cm) from embankments with slopes a s steep as 2:1 even though the barr ier may deflect 10 f t (3.1 m) o r more. However, i n the absence of , test data or other supporting information, i t is recom-

mended t ha t the G1 system be placed 10 f t (3.1 m) or more l a t e r a l l y from om5~11haents o r drop-offs with slopes steeper than 2:1.

REFERENCES --

1. Brucz, R. W . , Hahn, E . E . , Iwankiw, N. R . , "Guardrail/Vehicle Dynamic Interaction", Report No. FHWA-RD-77-29, March, 1976.

2. "Collis-ion Defoi-?ation Classif ication, Recomnended Practice J224a8', Society of Auturilotive E~gineers , New York, 1973.

3. Grahanl, M. D . , e+ a l . , "New Highway Barriers: The Practical Application of Theoretical Design", Highway Research Record 174, 1967.

4. "Guide fo r Sc12cting, Locating, and Designing Traffic Barriers", 1977 American Assoc ia t i~n of Sta te Highway and Transportation Officials (AASHTO).

5. " Reconanended Prxx!cres for Vehicle Crash Testing of Highway Appurtenances", Transportation Research Circular No. 191, Transportation Research Board, February, 1978.

6. Ross, H. E. , Jr., and Smith, D. G . , "Impact Behavior of Roadside Barrier on Nonlevel Terrain -- Crash Test Study", Research Report 3659-1, Texas Trans- portation In s t i t u t e , Texas A&M University, April, 1979.

7. "Vehicle Damage Scale fo r Traffic Accident Investigators", Traff ic Accident Data Project Bulletin No. 1, National Safety Council, 1971.

ACKNOWLEDGMENTS

Research reported i n th i s paper was sponsored by the Federal Highway Ad-

ministration under Contract DOT-FH-11-9343. The authors a re grateful to FHWA

for the i r permission t o publish th i s work. Mr. Morton S. Oskard of FHWA served as technical contract manager, and his guidance and cooperation were appre-

ciated.

NOTICE

The contents o f t h i s report re f lec t the views of the authors who are res-

ponsible f o r the facts and the accuracy of the data presented herein. The contents do ;lot necessarily ref lect the off ic ial views or policy of the Depart-

ment o f Transportation.

This report doss not constitute a standard, specification, or regulation.

TABLE OF ACCIDENT COSTS (Adapted from The NHTSA Accident Cost Data)

Assumptions

Fata l Accident Cost = $300,000 I n j u r y Accident Cost = 7,500 PDO Accident Cost = 500

Sever i ty Index

0 1 2 3 4 5 6 7 8 9

10

% PDO Accidents

% I n j u r y Accidents

EXAMPLE

SI = 5.7

Cost For S I 5.0 $20,025 Cost For SI 6.0 41,200

Di f ference = $21,175 70% o f Di f ference = 14,822

% Fata l Accidents

Total Acci dents

Cost For S I 5.7 = $34,847

REV1 SED A COST-EFFECTIVENESS SELECTION

PROCEDURE FOR B A R R I E R S

Introduction - This section contains a revised cost-effectiveness procedure for selection of barriers. The primary difference i s the change for present worth analysis t o annual cost analysis, thus, permitting comparison of alternatives of different service l ives.

Introduction

Collisions involving vehicles with roadside objects represent a problem inherent to any existing highuay facility. Consequently, roadside safety improvement programs have evolved to provide guidance in eliminating those problem locations where attention is vitally needed. For the most part, these programs share the following policy base.

Obstacles which may be removed should be eliminated. . Obstacles which may not be removed should be relocated laterally a in a more protected posltlon.

Obstacles which may not be moved should be reduced in impact severity. Breakaway devices and flattened side slopes offer such an improvement.

Obstacles which may not be otherwise treated should be shielded by attenua- tion or deflection devices.

While the above mentioned points of design summarize the available alternatives, the questions of "where, when or how" are often left unanswered. Limited funds are also a factor most agencies face. The designer is thus confronted with the problem of selecting those alternatives which offer the greatest return in terms of safety benefits.

The purpose of this cost-effective selection procedure is to provide a technique for comparing alternate solutions to problem locations. Present value of the total cost of each alternative is computed over a given period of time, taking into consideration initial costs, maintenance costs, and accident costs. Accident costs incurred by the motorist, including vehicle damage and personal injury, are considered together with accident costs incurred by the highway department or agency. Selection of the alternative with the least total cost would normally be made.

With regard to traffic barriers, the cost- effective procedure can be used to evaluate three alternatives:

1. Remove or reduce hazard so that shieldin* is unnecessary;

2. Install a barrier; or

The third option normally would be cost effective only on low volume and/or low speed facilities, or where the probability of accidents is 10%. With regzrd tc item 2, the procedure allows one to evaluate any number of barriers that can b e used to shield the hazard. Each location aad its alternatives should be approached on an individual basis. Through this method the effects of average daily traffic, offsei of barrier or hazard, size of barrier or hazard, and the relative severity of the barrier or the hazard ran be evaluated.

The procedure presented herein has been adopted from the work of Ross, et.al. ( L ) and permits objective evaluation of the options at a given site. fke procedure in- cluded in this document is nore generally applicable and is recorn!nenlec! for general use.

5.1.62 Applications Implementat Ion of the cost-effective procedure primarily Involves the determination of several Input values. The cmputatlons are slrnple and require only basic mathematics. It should be noted that dur ing the course of the text, the work nobstacle" Is used quite frequent1 y. In this context, the term Is meant to apply to either a hazard or improvement, whichever the case m y be. The following steps surnmarlze the procedure to be followed In the cost-effective analysis. 1. From existing or propose6 geometry de-

termine the following:

A = lateral placement of the roadside obstacle from EOP (in feet).

L = horizontal length of the roadside obstacle (in feet).

W = width of the roadsize obstacle (in feet).

2 . From volume counts or estimates, determine the average daily traffic, ADT (vehicles per d a y ) . This value should represent the two-way volume flow.

3 . Determine the encroachment frequency, E (vehicle encroachments per mile per year), from Figure 5.1.36. Figure 5.1.16 was obtained from data discussed previously. Other available data or

3. Do nothing, i.e., leave hazard unshielded. 25

adjustments of the above may be used at the discretion of the designer. This latitude offers an option to the user and helps to preserve the generality of the model.

4. Determine the collision frequency, Cf (accidents Ter year), from the appropriate nomograph given in Figures 5.1.17 and 5.1.16 (iependent on obstacle length). The nomographs combine the over-all genetry with a given encroach- nent freque-cy to yield the collision frequency. Collision frequency, Cf, is the predicted number of times a given obstacle will be impacted by an errant vehicle per year. The nomographs are used in the following manner. Locate 2nd r ~ r k the encroachment fre-

quency, Ef, on ;.ertical a x i s a

On horizontzl axis@locate the lateral placement, A , a:.: construct a vertical reference line :he full height of the graph.

4 Locate and M r k the point where the la tera l placement reference l lne Intersects the width, Y, curve In consideration.

+ Project a horizontal line to the r' from that point to the vertical axisflht and mark the point of intersection.

Locate and mark the point where the lateral placement reference line intersects the length, L, curve in consideration.

Project a horizontal line to the 1 ft from this point to the vertical a x i s 6 rnd mark the point of intersection.

across the points const uct a line a x i s 6 Mark the

point of intersection.

From the point dete mined construct a l i n e to vertical axisbkeeping approximately parallel to guidelines. Mark the point of intersection.

sfon frequency, Cf, where the line intersects the collision frequency axis. An example demonstrating the application of one of the nomographs is given in Figure 5.1.19. It may be necessary to adjust the collision frequency in locations where the Seometry and traffic conditions are critical. Off-ramp gore areas represent such a situation, and an upward adjustment factor of 3 has been suggested. Mathematically, the collision frequency is given in the ex- pression below.

where,

the variables A , L, W and E are as previously defined

and,

Y = the lateral displacement, in feet (metres), of the encroaching vehicle, measured from the edge of the traveled way to the longitudinal face of the roadside obstacle;

P[Y > . . . .I = probability of a vehicle .lateral displacement greater than some value. These probabilities may be taken from Figure 5.1.20;

and

J = the number of the 1-ft (.3 m) wide obstacle-width increment under investigation. (If the obstacle is not a vhole number of feet (metres) wide, the number of increments investigated is obtained by rounding the width down to the nearest whole foot (metre).

5. Assign a severity index to the ohs~acle of concern. Hazards can be denoted according to the hazard classification codes given in Table 5.1.11. It is suggested that the severity index be chosen on a scale of 0 to 10 according to the criteria given in Table 5.1.12. For example, if it is estimated that an impact with the obstacle will result in injuries or a fatality 60 percent of the time, select an index of 7. Correspond- ing to the index is an estimated accident cost which includes those costs associated with vehicle damage and occupant injuries and/or fatalities. F i g u r e 5.1.21 is a graphic represelltat ion of a c c i J e n t c o s t versus severity index. Discretion is advised in assigning severity indices and the designer is encouraged to exhaust all available objective data before resorting to judgment.

1 f t . = .3C5 n

Figure 5.1.20 Lateral Displacement Distribution

F i g 5 . 1 1 Average Occupant Injury and Vehicle Damage Costs (9 31

TABLE 5.1.11 HAZARD C L A S S I F I C A T I O N CODES

Note: C i r c l e d Codes denote Po in t Hazard -

Descriptor Codes I d e n t i f i c a t i o n Code

@ u t i l i t y po les (00) @ ~ r e e s (00) @ ~ g i d Signpost (01) single-pole-mounted

(02) double-pole-mounted (03) triple-pole-mounted (04) c a n t i l e v e r support (05) overhead s i g n br idge

@ Rigid Base Luminaire Support (00)

05. Curbs

06. Guardra i l o r Median B a r r i e r

GUARDRAIL END TREATMENT CODES i ?Jot tq~nnlnq u endlnq at structure-

Safety treated 2 Not beq~nnlq or endlnq d rtructurc -

k t safety heated 3 &glnnlnq or cndlng at structure-

Full- ha -ton 4 Bspmlng w m61rq d structure-

Not full-brom cunrction

07. Roadride Slope

(01) mountable design (02) non-mountable design less than

10 inches high (03) b a r r i e r design g r e a t e r than 10

inches high

(01) w-eection v i t h s tandard pos t spacing (6 f t-3 i n . ) ( including depa r t i ng g u a r d r a i l a t br idge)

(02) w-section with o the r than s tandard pos t spacing ( including depa r t i ng g u a r d r a i l a t br idge)

(03) approach gua rd ra i l t o bridge--decreased pos t spacing (3 it-1 in.) ad jacent t o br idge

(04) approach g u a r d r a i l t o bridge--pos t spacing no t decreased ad jacent t o br idge

(05) p o r t and cab le (06) Metal Beam Guard Fence ( ~ a r r i e r )

( i n median) (07) median b a r r i e r (QiB design o r

equiva len t

(01) eod p o e i t i v e elope (02) sod nega t ive r l ope (03) concrete-f aced poe i t i ve e lope (06) concrete-f aced negat ivc r l o p e (05) mbble rip-rap p o r i t i v e s l o p e (06) rubble rip-rap nega t iva e lope

TABLE 5.1.11 (cant. )

(00) 08. Ditch ( inc ludes e ros ion , r ip-rep runoff d i t c h e s , e t c. --dore not i nc lude d i t c h e s formed by i n t e r - eectbn of f r a t and back e lopes

Culver t s

I n l e t s

(01) headwall (o r exposed end of p i p e cu lve r t )

(02) gap between c u l v e r t s on p a r a l l e l roadways

(03) s loped c u l v e r t w i t h g r a t e (04) s loped c u l v e r t w i thou t g r a t e

(01) r a i s e d drop i n l e t ( t ab l e top ) (02) depressed drop i n l e t (03) s loped i n l e t

@ Roadway under Bridge (01) br idge p i e r s S t r u c t u r e (02) b r idge abutment, v e r t i c a l f a c e

(03) b r idge abutment, s loped f a c e

12 . Roadway over Bridge @ open gap between p a r a l l e l b r idges S t r u c t u r e

between p a r a l l e l

(03) r i g i d bridgerail-smooth and cow- t i n u o w cons t ruc t ion

(04) semi-rigid br idgera i l - ssooth and continuous corm tru c t i o n

(05) o t h e r br idgerai l - -probable penetra- t ion, snagging, pocket ing o r v a u l t i n g @ e leva ted gore abutment

13. Reta in ing Wall (01) face @ exposed end

Hiecel laneous Poin t (01) pedee ta l base > 6 i n . above Hazards ground, < 1 f t. diam,

(02) pedes t a l base > 6 i n . above ground, > 1 f t . d l = .

(03) h i s t o r i c a l monument < 1 f t . wide

(04) h i s t o r i c a l monument > 1 ft. v ide

'I'ABLl; 5 . 1 . 1 2 SEVERITY INDICES

Identificatfon Descriptor End Treatment Code Severity-Indrx Code Code Besinning Cndin~ A_____--

1. Utility Pole 1 0 - - 7.1

2. Trees 7 0 - - 8.0

3. Rigid Slgnpost 3 1 - - 4.7 3 2 - - 7 . 2 3 3 - - 7.2 3 4 - - 7.2 3 5 - - 8.1

4. Rigid Base Luinaire Support 4 0 - - 7.5

5 . Curbs 5 1 - - 2.4 5 2 - - 4.1 5 3 - - 3.7

6 . Guardrail or Median Barrier 6 1 1 1 3.7 6 1 1 2 4.0 6 1 1 3 3.6 6 1 1 4 4.5 6 1 2 1 5.6 6 1 2 2 5.7 6 1 2 3 5 . 3 6 1 2 4 5.7 6 1 3 1 3.3 6 1 3 2 3 . 3 6 1 3 3 3 . J 6 1 3 4 4.6 6 1 4 1 4 . 5 6 1 4 2 4 . 7 6 1 4 3 4 . 5 6 1 4 4 5.0 6 2 1 1 3.9 6 2 1 2 4.2 6 2 1 3 3.8

Identification Descriptor End Treatment Code Severity-Index - Code Code Beginning Ending --

6 2 1 4 4.7 6 2 2 1 5.8 6 2 2 2 5.9 6 2 2 3 5.5 6 2 2 4 5.9 6 2 3 1 3.5 6 2 3 2 3.5 6 2 3 3 3.5 6 2 3 4 4.8 6 2 4 1 4.7 6 2 4 2 4.9 6 2 4 3 4.7 6 2 4 4 5.0 6 3 1 1 3.7 6 3 1 2 4.0 6 3 1 3 3.3 6 3 1 4 4.5 G 3 2 1 5.6 6 3 2 2 5.0 6 3 2 3 3.9 6 3 2 4 5.0 6 3 3 1 3.2 6 3 3 2 3 .2 6 3 3 3 3.2 6 3 3 4 4.4 6 3 4 1 4.0 6 3 4 2 4.5 6 3 4 3 3.9 6 3 4 4 4.7 6 4 1 1 3.7 6 4 1 2 4.0 6 4 1 3 3.6 6 4 1 4 4.5 6 4 2 1 5.6 6 4 2 2 5.7 6 ft 2 3 5.3 6 4 2 4 5.7 6 11 3 1 3.3 6 4 3 2 3.3 6 4 3 j 3.3 6 4 3 4 4.6 6 4 4 1 4.5 6 4 4 2 4.7

-

TABLE S . l . 1 2 SEVERITY INDICES (cont.)

Ident i f i c a t i o e Descriptor Ead T r u h a n t Code Severity-Index Code Cod e Beginniw t n d i n ~

6 4 b 3 4.5 6 4 4 4 5.0 6 5 1 1 3.9 6 5 1 2 3.9 6 5 1 3 3.9 6 5 1 4 3.9 6 5 2 1 3.9 6 5 2 2 3.9 6 5 2 3 3.9 6 5 2 4 3.9 6 5 3 1 3.9 6 5 3 2 3.9 6 5 3 3 3.9 6 5 3 4 3.9 6 5 4 1 3.9 6 5 4 2 3.9 6 5 4 3 3.9. 6 5 4 4 3.9 6 6 1 1 4.4 6 6 1 2 4.4 6 6 1 3 4.4 6 6 1 4 5.0 6 6 2 1 5.6 6 6 2 2 5.7 6 6 Z 3 5.3 6 6 2 4 5.7 6 6 3 1 4.0 6 6 3 2 4.4 6 6 3 3 4.0 6 6 3 4 4.6 6 6 4 1 4.5 6 6 4 2 4.7 6 6 4 3 4.5 6 6 4 4 5.0 6 7 1 1 4.2 6 7 1 2 4.2 6 7 1 3 4.2 6 7 1 4 4.2 6 7 2 1 4 . 2 6 7 2 2 4.2 6 7 2 3 4.2 6 7 2 4 4.2 6 7 3 ' 1 4.2 6 7 3 2 4.2 6 7 3 3 4.2 6 7 3 4 4.2 6 7 4 1 4.2 6 7 4 2 4.2 6 7 4 3 4.2

J 6 7 4 4 4.2

ldentif i c a t i on Descriptor End Treatment Code Swerit y-Index . - Code Code Beginning Ending

. --

7. Roadside Slope 7 1 - - 3.0 7 2 - - 3.0 7 3 - - 2.5 7 '4 - - 2.5 7 > - - 5.1 7 7 - - 5.1

8. Ditch 8 1 - - 0.0

9. Culverts 9 L - - 7.9 9 2 - - 5.5 9 1 - - 3.3 9 I - - 7.7

10. I n l e t s 10 L - - 5.7 10 2 - - 3.1 10 3 - - 3.3

11. Roadway Under Bridge S t ruc ture 11 1 - - 9.3 11 2 - - 9.3 11 3 - - 2.5

12. Roadvq Over Bridge S t ruc ture 1 2 1 - - 7.2 12 2 - - 5.5 12 3 - - 3.3 12 4 - - 3.0 12 5 - - 9.3 12 6 - - 9.3

13. Retaining Wall 13 1 - - 3.3 13 2 - - 9.3

14. U f r c e l 1 . n . o ~ ~ Point Hazards

14 1 - - 7.5 14 2 - - 9.3 14 3 - - 7.5 14 4 - - 9.3

13. Ca l cu l a t e t h e t o t a l annual c o s t , C A T , from the fol lowing equat ion:

Ir Metric Equivalent Equation

C = &Q [(L + 19.2) P[Y 2 A] J = W 25 - 1

+ 5.14 Z P[Y , A + 1.8 + --]I J=l

E i n Encroachments/km/yr f L, Y , A, and W i n metres

(The width of J may be taken a s 1 metre wi th t he number of J u n i t s equa l W rounded t o t h e n e a r e s t whole number.) This equa t ion may be implemented d i r e c t l y i n t o t h e c o s t a n a l y s i s o r used a s a double- check f o r t h e c o l l i s i o n frequency nomographs. Computation of t he c o l l i s i o n frequency f o r

)mul t ip le o b j e c t s r equ i r e s s p e c i a l procedures.

CRF, SF = c a p i t a l recovery and s ink ing fund f a c t o r f o r some c u r r e n t i n t e r e s t r a t e

CA, * c1 [CRFl + CDCf + CM + COVDCf - CS (SF)

o r , t o determine those c o s t s which a r e d i r e c t l y incur red by t h e highway depa r t - ment ( o r implementing agency), (CA ), use t he equat ion below: D

C ~ D = C, [CRF] + CDCf + CM - CS(SF)

These t o t a l annual c o s t s r e p r e s e n t an est imated value r e l a t e d t o some appurtenance/ b a r r i e r . Any number of l o c a t i o n s o r a l t e r - na t i ve s may be evaluated by u t i l i z i n g t h i s , method, and a p r i o r i t y l i s t i n g may be e s t ab l i shed . The a l t e r n a t i v e wi th t he l e a s t t o t a l annual c o s t i s t he p r e f e r a b l e a l t e r n a t i v e . Summary of Variable Definition?-

A = l a t e r a l placement of t h e roadsidc obs t ac l e from EOP ( f e e t ) [metre]

6 . Determine t h e i n i t i a l c o s t o f t h e obs t ac l e . CI. I f it i s a l ready i n p l ace , L = hor i zon t a l l ength of t h e roads ide i ts i n i t i a l c o s t may be assumed t o equal obs t ac l e ( f e e t ) [metre] zero. For example, i f a group of median b r idge p i e r s had been i n ex i s t ence W = width of t he roads ide o b s t a c l e f o r t e n yea r s , then t h e i n i t i a l c o s t of ( f e e t ) [metre] a no improvement a l t e r n a t i v e would be taken t o be zero. On t h e o t h e r hand, ADT = average d a i l y t r a f f i c ( v e h i c l e s pe r improvements t o such a hazard would r e - day, two-way) q u i r e i n i t i a l expenditures which should be s o designated. encroachment frequency (encroach-

E f = ments per mile per year ) [encroach- 7 . Determine t he average damage c o s t t o nents per ki lometre per year]

t he o b s t a c l e par acc ident , CD (presen t d o l l a r s ) . Cf = c o l l i s i o n frequency ( acc iden t s pe r

8 . Determine t h e average maintenance cos t year)

- per year , Cr4, as soc i a t ed wi th t he upkeep SI * s e v e r i t y index of t he o b s t a c l e (p r e sen t d o l l a r s ) .

CI = i n i t i a l c o s t of t he o b s t a c l e 9 . Determine t he average occupant i n ju ry (presen t d o l l a r s )

and veh i c l e damage c o s t per accident, COVD, which would be expected a s a CD = average damage c o s t per a cc iden t r e s u l t of a c o l l i s i o n (p r e sen t d o l l a r s ) . incurred t o t h e obs t ac l e (p r e sen t Table 5.1.12 and F igure 5.1.21 may be d o l l a r s ) used t o determine COVD i n t he absence of more d e f i n i t i v e da ta . Di rec t i n t e r - CH = average maintenance c o s t per year po l a t i on of t he cos t t a b l e i n Figure f o r the obs t ac l e (presen t d o l l a r s ) 5.1.21 i s suggested t o i nc r ea se t he accuracy of t h e est imate. COVD - average occupant i n j u r y and v e h i c l e

damage cos t per acc ident ( p r e sen t 10. Determine t he u se fu l l i f e , I, of the d o l l a r s )

o b s t a c l e (yea r s ) . CS = est imated salvage value of t h e

13. Determine t he c a p i t a l recovery and s ink- obs t ac l e ( f u t u r e d o l l a r s ) ing fund f a c t o r s . CRF and SF f o r t h e u s e f u l l i f e . "T" and a cu r r en t i n t e r e s t C A ~ - t o t a l present worth c o s t a s soc i a t ed r a t e come from Tables 5.1.13 and 5.1.14. with t h e obs t ac l e ( d o l l a r s )

1 2 . Est imate t he expected salvage va lue of CAD = t o t a l present worth d i r e c t c o s t t he obs t ac l e , CS, a t t he end of i t s use- a s soc i a t ed wi th t h e obs t ac l e f u l l i f e ( f u t u r e d o l l a r s ) . ( d o l l a r s )

..

r

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C . c d o o d d d d d d d d o d d d d d d d d d o o d

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o a ~ m ~ o m h b m b h - a ~ a m ~ o h a d m - o m a h a ~ ~ o ~ o F ~ ~ ~ ~ ~ ~ v ) ~ ~ ~ ~ N N N N ~ F - - F - ~ o o ~ o ~ ~ ~ ~ ~ , ~ ~ ~ o ~ o o ~ ~ o ~ ~ o ~ o o ~ ~ o , ~ o o o o o o o o ~ o o

. . . . . . . . . . . . . . F ~ d o o o o o o o o o o o o o o o o o ' d d ~ ~ ~ ~ ~ ~ ~ ~

O h m m h N m ~ h w h O * * b O h b N 0 Q m d m N C - O m c O h o h ~ ~ w m o m h w m m b m m m ~ ( ~ ~ ~ ~ - ~ ~ - ~ ~ o o o 0 * q ~ N ~ ~ ~ 0 0 0 0 0 * q 0 ~ 0 0 * 0 0 * 0 C 0 0 0 c 0 0 0 0 0 0

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5.1.35 Example 1 - Roadside Slope

In the-first example, it is desired that criteria be established to indicate when it is cost-effective, in terms of ADT and side- slope. to shield an embankment. It is assumed :hat an operating speed of approximately 60 mph (96.6 km/hr) exists. The general gecletry of the roadside is illustrated in Figure j.1.22. For purposes of analysis, both :he average daily traffic, ADT, and the roadside slope will be considered as varia- b l e ~ . -;slues assigned to other variables are a s z u - e l ta fall within a reasonable expected r3cge. Tke following analysis will consider shielCj-3 with a roadside barrier first and then rke alternative of no shielding.

Fizzre 5.1.22 Roadside Slope Geometry

Before this alternative can be considered in the ccst-effectiveness procedure, the flared end-treatnent geometry should be established by i?;leacnting the barrier flare criteria set f ~ r t h in Section 5.1.44. On the basis of these criteria, the flared sections uere as- suzeC :o exhibit the following general geonetry:

The average offset equals 15 ft (4.6 m). The horizontal length of the flared sections equals 256 ft (78.0 m) .

a And the total rail length needed equals 2 5 7 ft (78.4 m).

These lengths represent the total length of need of the flared section plus a breakaway cable terminal treatment.

In continuing, the roadside barrier analysis involves two distinct computations. In the first case, costs associated with the flared portion of the barrier are computed. Then, costs associated with the barrier proper or the tangent section are computed. The two are then combined to determine the total cost. However, a minor adjustment must be made in determining the collision frequency since the flared portion and the barrier proper are joined at a common point. The following general rule applies in this acd other such cases:

For two objects joined together, use the actual length (L) of the object with the highest severity index (SI) and subtract 31.4 (9.6 for metric equivalent) from the length of the other object .*.hen determining their respective collision frequencies.

This rule is illustrated in the following example. Note that the cost determination steps follow the format previously outlined.

Flared End Treatment

\i = 1 ft (.305 m) (rail width) 2. ADT = 10,000 (assumed)

4. Cf = 0.078 (.Actual length is used to determine C because 51 for flared section is higher than for barrier proper .)

5. Code 06-01-1; SI = 3.7

6 . CI = $lf.CC (assumed) per foot at 257 ft (78.39 n)

8 . CM = $ 1 . 5 0 per foot per year (assumed) at 257 ft (58 .4 m);

9. COvD = $7,192 at ST = 3.7 (Figure 5.1.21) 10. T = lS years

11. CRF = 0.117 at an assumed rate of 8%

SF = 0.037

1 2 . 33.00 per foot (assumed) at 257 ' ft (78.4 m)

Barrier Proper

1. A = 10 ft (3.05 m)

L = 1000 ft (305 m) W = 1 ft (.31 m)

2. ADT = 10,000

3. Ef = 3.2

4. Cf = 0.29 based on L - 31.4 or 968.6 ft (295 m) (See Example 1)

5. Code 06-01-3-2; SI = 3.3 (See Table 5.1.10)

6. CI = $13.00 per foot (assumed) at 1000 ft (305 m);

CI = $13,000 7. C D a $225(asswned) 8. CM = $1.50 per foot per year (assumed)

at 1000 ft (305 m); CW = $1,500

9. COVD = $5,874 at SI = 3.3 10. T = 15 years

11. i = 82

CRF = 0.117

SF = 0.037

12. C S = $ 3 . 0 0 p e r f o o t ( a s s u m e d a t 1,000 ft (305 m);

Cs = $3,000

= 1521 + 65 + 1500 + 1703 - 111

CAT a $4,678 c~~ a $2,975

TOTAL C A ~ = 1327 + 4678 $6,005 TOTAL C A ~ = 766 + 2975 - $3,741

These two total costs represent values associated with an average daily traffic equaling 10,000 vehicles per day. The above steps are repeated for higher values of ADT until enough dala points are determined to plot CAT versus ADT. Ultimately, the total barrier values as a function of average daily traffic will be used in the alternative comparison.

Another alternative which should be considered involves no shielding at all. This alternative requires no direct expenditures since it is assumed that the problem involves existing roadways.. Consequently, only the total costs (to include occupant and vehicle damage) can significantly indicate the benefits/disbenefits associated with no shielding of the embankment.

For purposes of analysis, four slopes have been considered as variables in addition to the average daily traffic control. These slopes and their respective estimated severities for assumed site conditions are as follows:

(3.5:l) slope - severity index equals 3.5

(3:l) slope - severity index equals 4.0 (2.5:l) slope - severity index equals 4.5, and

(2:l) slope - severity index equals 5.0

(Note that for fills steeper than about 3:l the height of fill should be expected to influence severity .) Although the slope severities are not spe- cifically identified in the hazard inventory information, a severity index is listed for a negative slope. Assuming that this negative slope represents an average situation and that a 4:l slope is approximately average, then the severity index of a 4:l slope would be found to equal 3.0. Furthermore, since the severity index of the roadside barrier is greater L:lo, ,, .;,, + . ; slope, then in no way can the barrier be more cost-effective. By taking the average slope as a base, the severities of the other gradients were estimated, and occupant and vehicle damage costs were assigned. The initial, damage, maintenance, and salvage costs were all taken to be zero since it is assumed that the existing geometry requires no direct expenditures. By choosing the average daily traffic again to equal 10,000 vehicles per day and considering a 3.5:l slope, the costs may be determined by the following steps:

2. A D T - 10,000

3. Ef - 3.2 4. Cf = 0.30

5. S I - 3 . 5

8. $ - $0 9. COVD $6,535 tit $1 = 5 . 5

10. T - 15 years

11. CRF = C.i1 ' at an assumed Intwost

rat. of 81 SF = 0.037

12. c, - to

Total costs for the four slopes and varying .;lumes are calculated in a similar manner to provide the basis of comparison for the no protection alternative. Comparison

The various situations can best be compared by plotting curves of total present cost versus average daily traffic. Such a set of curves is shown in Figure 5.1.23. By interpreting the data the following conclusions may be drawn:

1. Unprotected slopes of 3:l and flatter are more cost-effective than the batrier for an average daily traffic up to and in excess of 50,000 vehicles per day; i.e., the barrier is not warranted;

2. The 2.5:l slope, unprotected, (assumed severity 4.5) becomes less cost-effective than the barrier for an average daily traffic equal to or above 12,000 vehicles per day; and

3. The 2:l slope, unprotected, (assumed severity 5.0) becomes less cost-effective than the barrier for an average daily traffic equal to or above 10,000 vehicles per day.

This analysis serves to provide some insight as to where roadside barrier protection of slopes ray or may not be more cost- effective. General design guidelines or policies may be established and, ROre im- portantly, ~ustified in terms of the highest returns in safety.

11.000 t BARRIER MORE COST EFFECTIVE

UNPROTECTED SLOPE MORE COST- EFFECTIVE

Figure 5.1-23. Cost Comparison Curves

General Comments

1. The a n a l y s i s , a s p r e s e n t e d i n t h i s i~roblem, invo lves on ly t h o s e c o s t s a s s o c i a t e d u i t h one s i d e of t h e highway f a c i l i t y . I f t h e same c o n d i t i o n s e x i s t on t h e o p p o s i t e s i d e , then t h e t o t a l c o s t s f o r bo th s i d e s 'would be doub le t h o s e p r e v i o u s l y determined.

2 . :lie avcrage d a i l y t r a f f i c should r e p r e s e n t t h e t ~ ~ o - u a y volume f low s i n c e t h e volume s p l i t , i s b u i l t i n t o t h e a n a l y s i s procedure . This adjustment i s e f f e c t e d by t h e c o l l i s i o n frequency nomographs.

3 . The u s e f u l l i f e o f a r o a d s i d e s l o p e i s taken t o be 1 5 y e a r s , which is obv ious ly n o t t h e r e a l case . However, t h e r e is l i t t l e d i f f e r e n c e i n t h e economic f a c t o r s beyond 15 y e a r s .

4 . This example i l l u s t r a t e s how t h e procedure c a n be used t o de te rmine t h e c o s t - e f f e c t i v e n e s s of t ~ ~ o b a s i c o p t i o n s , i . e . , b a r r i e r s h i e l d i n g v e r s u s no s h i e l d i n g of s l o p e s , f o r a g iven l o c a t i o n . Although n o t cons ide red h e r e , t h e n e x t d e s i r a b l e s t e p may be t o e s t a b l i s h a p r i o r i t y o r ranking systzm f o r reduc ing hazards w i t h i n a g i v e n roadway system. The o b j e c t i v e would be t o make inprovements t h a t o f f e r t h e g r e a t e s t r e t u r n i n terms o f s a f e t y . The fo l lowing equa t ion may be used f o r de te rmin ing a ranking f a c t o r , R:

c - CAI R =

-*DI -

C = annurl Z C S Z a s s o c i a t e d w i t h t h e .'H unsh ie lded hazard over t h e p e r i o d

T;

C = annual c o s t a s s o c i a t e d k i t h t h e A~ improvement over t h e p e r i o d T; and

C = annua l c o s t t o t h e highway d e p a r t - ment o r agency a s s o c i a t e d w i t h t h e inprovement.

Improvements should be made t o t h o s e hazards having the h i g h e s t v a l u e R f i r s t . Note t h a t i f t h e numerator i s n e g a t i v e , t h e improvement would no t be c o s t - e f f e c t i v e . I n Example 1, t h e rank ing f a c t o r f c r p l a c i n g a r o a d s i d e b a r r i e r t o s h i e l d t h e 2:1 s l o p e (assumed s e v e r i t y 5 .0 ) f o r an ADT o f 25,000 would be computed a s fo l lows :

c = $16.710 (Slope) (From Figure A~ , 5.1.21)

c - 5 10,612 ( B a r r i e r ) (From Figure A~ 5.1.21)

CrlilI = $3 ,530 (From p r e v i o ~ ~ s c a l c i ~ l n t i o n s )

t h u s

R = 16,710 - 10.612 3.530

5.1.54 Example 2 - Bridge P i e r s

Flguro 5.1.24 shows a typlcal b l d g o p l u hnz- ard. T h r a al twnat lvos w I I I be cons ldwd In tho cost analysls as fo l lws : 1. NO p r o t e c t i o n of t h e b r i d g e p i e r s

2. P r o t e c t i o n of t h e b r i d g e p i e r s w i t h a r o a d s i d e b a r r i e r r a i l

3. P r o t e c t i o n o f t h e b r i d g e p i e r s w i t h a combinat ion r o a d s i d e b a r r i e r r a i l and c r a s h c u s h i o n system

Subsequent t o t h e c o s t c a l c u l a t i o n s , a comparison o f t h e t h r e e o p e r a t i o n s w i l l b e made based on a p r e s e n t worth b a s i s , and t h e most c o s t - e f f e c t i v e d e s i g n w i l l b e i d e n t i f i e d . Note t h a t t h e s t e p s i n t h e a n a l y s i s cor respond t o t h o s e d e s c r i b e d i n t h e i n t r o d u c t i o n of t h e s e c t i o n above.

F i g u r e 5.1.24 Bridge P i e r Hazard

P r o t e c t i o n c r i t e r i a o u t l i n e d prev ious ly , (See Sec t i on 5.1.44) t h e placement va lues t o be used i n t h e

1. A - 23.5 f t (7.17 m) o r approximately c o s t procedure were assuaed t o be t h e following: 23 f t (7.02 m);

1. The average o f f s e t f o r t h e f l a r e d s e c t i o n s L = 32 f t (9.75 m) and: equa l s 16 f t (4.88 m)

2. ADT - 75,000 (assumed]

4. Cf 0.17

5. Code -01; SI = 9.3 (See Table 5.1.10) 6. CI = $0 ( s ince t h e p i e r s a r e e x i s t i n g )

8, CM = $0 (assumed) 9 . cOVD $16g.;nn -+ q~ = 1

10. T = 20 y e a r s

11. CRF' 0.102 I a t an i n t e r e s t r a t e of 88 12. SF ' 0.022

o r cons ider ing c o l l i s i o n s wi th both ends of t he br idge p i e r hazard,

2. The p ro j ec t ed l ong i tud ina l l ength o f t he b a r r i e r f l a r e equa l s 151 f t (46.01 m) 3 . The a c t u a l l e n g t h of t h e b a r r i e r f l a r e equa ls 153 f t (46.67 m). I n determining t h e t o t a l c o s t s a s soc i a t ed wi th roads ide b a r r i e r p r o t e c t i o n , two sepa ra t e c a l c u l a t i o n s w i l l be made - one cons ider ing c o l l i s i o n s w i th t h e b a r r i e r f l a r e and t h e o t h e r involv ing impacts t o t h e b a r r i e r proper . The sum of t he se two c o s t s w i l l r ep re sen t t he t o t a l va lue a s soc i a t ed wi th t h e roads ide bar - r i e r a l t e r n a t i v e . Note t h a t c o s t s f o r one d i r e c t i o n of t r a v e l a r e computed, then doubled, t o ob t a in c o s t s f o r both d i r e c t i o n s of t r a v e l . I t i s assumed t h a t a crashworthy end t rea tment is used a t t h e upstream te rmina l .

B a r r i e r F l a r e

1. A - 16 f t (4.88 m),

2. ADT - 75,000

3. Ef - 31.0

4. Cf - 0.52 (Actual l e n g t h i s used t o determine C , because SI f o r f l a r e d s ec t fon is higher than f o r b a r r i e r proper .)

5. Code 06-01-1-1 SI = 3.7 (Table 5.1.10) 6. CI - $13.00 p e r f o o t ( a s s u e d ) a t

153 f t (46.67 m), t hus

These f i g u r e s r ep re sen t t h e p r e sen t c o s t s 7. CD = $225 (assumed] . -

as soc i a t ed wi th no p ro t ec t i on t o t h e roadway hazard. The t o t a l c o s t , a s would be expected, " $1.50 pe r f o o t per year (assumed) i s q u i t e s u b s t a n t i a l due t o t h e s e v e r i t y a t 153 f t (46.67 m); a s soc i a t ed wi th impacting a f i x e d br idge p i e r , while t h e t o t a l d i r e c t c o s t i s zero s i n c e no = $230

, - improvements a r e involved, Although t h e e x i s t i n g geometry may n o t o f f e r t he b e s t 9. COVD = $7,192 a t SI = 3.7 a l t e r n a t i v e , i t must be ca l cu l a t ed f o r use T = 20 y e a r s as a b a s i s i n comparison.

11. CRF - 0.102 Roadside Ba r r i e r j a t 8 t SF - 0.022 Before t h e c o s t a n a l y s i s can be implemented

CS 11,50 per foot (asswed) at f o r t h i s op t ion , s p e c i f i c a t t e n t i o n needs t o .be d i r e c t e d toward i d e n t i f i n g t h e b a r r i e r 153 f t (46.67 m) f l a r e geometry. Prom t h e g a r r l e r f l a r e C, - $250

B a r r i e r P roper

1. A = 13.5 f t (4.12 m); L = 32 f t (9.76 in); and

2 . ADT - 75,000

4. C f = . 1 7 B a s e d o n L - 3 1 . 4 - 0 . 6 f t (0.2 m) (See r u l e i n S e c t i o n 5.1.52.)

5. Code 06-01-3-2 S I = 3.3 (Appendix El 6. C I = $13.00 p e r f o o t (assumed) a t

32 f t (4 .12 m); t h u s , C I = $416 7. CD = $225 (assumed) 8. $1.50 p e r f o o t p e r y e a r (assumed)

a t 32 f t ( 4 . 2 m ) t h u s

10. T = 20 y e a r s

11. CRF = 0.102

12. CS = $1.50 p e r f o o t (assumed) a t 32 f t (4.12 m); t h u s CS = $48

The t o t a l b a r r i e r c o s t s may now be found by t o t a l i n g t h e v a l u e s f o r t h e f l a r e and t h e b a r r i e r p roper . Furthermore, t h e t o t a l amounts c o n s i d e r i n g s h i e l d i n g f o r bo th s i d e s may be a t t a i n e d by doub l ing t h e cos'ts a s s o c i a t e d w i t h c o l l i s i o n s from one s i d e .

There fore , f o r p r o t e c t i o n t o one end: T o t a l CA - 4285 + 1078 = $5,363

T

f o r p r o t e c t i o n o f b o t h ends:

T o t a l C = .$10,726 "T

T o t a l CA = $1,248 D

Roadside B a r r i e r / C r a s h Cushion System

The t h i r d a l t e r n a t i v e c o n s i d e r e d i n t h e b r i d g e p i e r a n a l y s i s w i l l be an i n t e g r a t e d c r a s h c u s h i o n - l o n g i t u d i n a l b a r r i e r system. The c r a s h cush ion w i l l be u t i l i z e d as a n end t r e a t m e n t t o s h i e l d t h e end p i e r s and t h e ends o f t h e r o a d s i d e b a r r i e r . The r o a d s i d e b a r r i e r i s p l a c e d a l o n g t h e 32 f o o t l e n g t h (9.8 m) t o s h i e l d t h e i n t e r i o r p i e r . C o s t s f o r each o f t h e subsystems may b e de te rmined g iven t h e i r r e s p e c t i v e geomet r i cs , and a t o t a l p r e s e n t worth may be f i x e d .

Crash Cushion - End Treatment 1. A = 21 f t (6.4 m),

L = 25 f t (7.6 m),

2. ADT = 75,000 (assumed)

4 . Cf = 0.12 Based on L - 31.4 = -6 .4 f t (-2.0 m) (See r u l e i n S e c t i o n 5.1.53)

Code 15-00-0-0 S I = 1 .0 (Tab le 5.1.10) CI = $ 5,000 (assumed) CD = $1,000 (assumed) CM - $150 (assumed)

COW = $2,095 a t SI = 1 . 0 T = 20 y e a r s

CRF = O,' a t a n assumed i n t e r e s t I SF 0.022 rate of

T o t a l C = 545 + 79 - $624 A~

Roadside w e r

1. A = 21 f t (6.4 m ) , L = 32 f t (9.8 m ) ,

2 . ADT = 75,000

4. 0.19 (Actual l e n g t h i s used t o Cf ' determine C because SI f o r road-

s i d e b a r r i e g i s h igher than f o r c r a s h cushion.)

5. Code 06-01-3-3 SI = 3.3 (Table 5.1.10) 6 , CI - $13.00 p e r f o o t (assumed) a t

32 f t (9.8 m); t h u s C I = $416 7. CD = $225 (assumed) 8. C M = $ 1 . 5 0 p e r f o o t p e r y e a r (assumed)

a t 3 2 f t (9.8 m ) ; t h u s ,

10. T = 20 y e a r s

il' CRF = 0.102 a t an assumed i n t e r e s t SF = 0.022 1 r a t e o f 82 CS = $1.50 per f o o t (assumed) a t

32 f t (9.8 m); t h u s CS = $48

Consider ing bo th t h e c o s t s f o r t h e a t t e n u a t o r and t h e l o n g i t u d i n a l b a r r i e r , t h e t o t a l system p r e s e n t worth v a l u e s may be compared a s fol lows:

For p r o t e c t i o n of one end:

T o t a l C = 1031 + 1248 = $2,279 AT

T o t a l CA = 780 + 132 $912 D

and f o r s h i e l d i n g f o r both s i d e s :

T o t a l C, = 2 (2279) = $4,558

T o t a l C *D = 2 (912) = $1,824

Comparison

Table 5.1.15 summarizes t h e r e s u l t s of t h i s example. By c o l l e c t i v e l y reviewing t h e t h r e e proposed a l t e r n a t i v e s , s e v e r a l obse rva t ions and conc lus ions may be o u t l i n e d . However, t h e s i g n i f i c a n c e of t h e s e obse rva t ions must be weighed i n l i g h t of t h e assumptions made and t h e v a l u e s ass igned t o t h e v a r i o u s pa ra - meters. While t h e s e va lues a r e thought t o be t y p i c a l , they may n o t be r e p r e s e n t a t i v e of a11 a r e a s .

1. While t h e no s h i e l d i n g a l t e r n a t i v e r e - q u i r e s no d i r e c t expend i tu res , it does r e p r e s e n t a ve ry s u b s t a n t i a l t o t a l annual c o s t i n terms of a c c i d e n t l o s s e s .

2. On a n annual c o s t b a s i s , t h e roads ide b a r r i e r / c r a s h cushion system o f f e r s the b e s t a l t e r n a t i v e . However, it does r e q u i r e a somewhat h i g h e r d i r e c t expend i tu re .

3 . The rank ing f a c t o r i n d i c a t e s t h a t of t h e two improvements, t h e roads ide b a r r i e r would p rov ide t h e g r e a t e s t r e t u r n per d o l l a r spen t .

TABLE 5.1.15 EXAMPLE COMPARISON

I

Ranking Factor, R

- -

19.1

16.4

Total Annual Cost. CA ($1 T

$34,545

$10,726

f 4,553

OPTION

1. No Shfelding

2. Shielding by Roadside Barrier

3. Shleldlng'by Crash Cushfonl Roadside Barrier

i

Dl rect Annual b s t , C A ~ ( $ 1

0

$1,248

$1,824

General Comments

1. P r a c t i c a l l y speaking, t he main i n t e r e s t i n comparing a l t e r n a t i v e s two and t h r e e i s t o ob j ec t i ve ly dec ide whether t h e s h o r t e r , more expensive and l e s s severe c r a sh cushion would/would no t en joy an advantage over t he longer , lower c o s t and higher s e v e r i t y b a r r i e r r a i l .

2. The main purpose o f t h i s example i s t o denons t ra te t h e use of t h e c o s t - e f f e c t i v e n e s s approach i n weighing s e v e r a l a l t e r n a t i v e s o l u t i o n s f o r one problem loca t i on . Other roads ide hazard l o c a t i o n s may be evaluated i n a s i m i l a r manner t o organize a complete f a c i l i t y inventory and a s e t of ranking f a c t o r s .

5.1.55 Example 3 - Elevated Gore Abutment

In t h i s example, an e l eva t ed gore abutment has been chosen f o r a n a l y s i s , and both c o s t s f o r t he hazard and an improvement w i l l be determined. By r e f e r enc ing t he layout shown i n F igure 5.1.25, t hose i npu t s necessar f o r t he ca1cu l a t i 0ns may be obtained, and t i e procedure may be i n i t i a t e d . Also, h igher than normal e n c r o a c h e n t s t h a t a r e common t o such a l o c a t i o n w i l l be considered i n t he a n a l y s i s , and adjustments w i l l be made according ly . Furthermore, t he eva lua t ion w i l l con- s i d e r only c o l l i s i o n s wi th t he exposed gore and c r a sh cushion, whichever t he case may be. Also, t he equa t ion f o r Cf w i l l be appl ied i n l i e u of t he noeographs t o demonstrate i t s use.

M A I N L A N E S -

ONE D l R E C T l O N - r 8' I

TOTAL TWO-WAY ADT=80,000

E x i s t i n g Hazard

1. A = 19 f t (5.8 m); L = 1 f t (.SO5 m); and W = 4 f t (1.2 m)

2. ADT = 80,000

4. Cf by using equat ion may be de tennined a s below:

= 0.17 and by apply ing an ad- !f justment f a c t o r of 3.0 f o r h igher t han normal encroachments (assumed),

Cf ( ad jus ted) = 3 (0.17) = 0.52 5 . Code 12-06-0-0 S I = 9.3 (Table 5.1.10) 6. CI = $0 7. CD - $0 (assumed) 8. CM = S O (assumed) 9. COVD = $169,412 a t SI = 9.3

10 , T = 15 yea r s 11. CRF = 0.117 I a t an assumed i n t e r e s t SF 0.037 rate

Crash Cushion Imoro-femcnt -

1. A - 17 f t (5.2 m); ' L = 25 f t (7.6 n); and

W = 8 f t ( 2 . 4 m) 2. ADT = 80,000

4 . Cf by us ing t h e equa t i on may b e d e t e r - mined a s below:

Figure 5.1.25 Elevated Gore Abutment

Cf = 0.27 and by applying an adjustment factor of 3.0 for higher than normal encroachments (assumed)

Cf (adjusted) = 3 (0.27) = 0.81

5. Code 15-00-0-0 SI 1.0 (Table 5.1.10)

6. CI = $5,000 (assumed) 7. CD = $1,000 (assumed)

C~ = $200 (assumed)

10. T = 15 years

at an assumed interest rate of 8k

12. CS = SO (assumed)

By comparing the total costs related to each of the two situations, it may be seen that from a safety standpoint the advantage ob- viously lies with the improvement alternative. The ranking factor for this site would be 53 which further points out the benefits, in terms of increased safety, that can be real- ized by installing a crash cushion at such a zone.

In those locations where the traffic-geometric relationships become critical, the collision frequency may be adjusted upward at the discretion of the designer. A factor of 3.0 has been proposed for gore areas, and this seeins to be a legitimate number; however, in locations where the variables are not so critical, possibly a lower factor would be appropriate. The decision on such an adjustment would rely strictly on the user's knowledge of the field and his engineering judgment.

5.1.56- Example 4 - Isolated Roadside Obstacles

As has been emphasized throughout this section, the most desirable roadside is one that is relatively flat and free of roadside hazards. If ample recovery room is provided, a driver of an errant vehicle will be able to return to the traveled way or safely stop the vehicle. Removal or relocation of hazards, or the installation of a breakaway device should always be the first option considered. How- ever, various situations may sonetimes dictate that isolated obstacles such as small trees or small utility poles be located within the desirable recovery area. In such cases, the designer often is faced with the question: Should the obstacle be shielded by a barrier, even though it is obvious that the hazard potential of the barrier is less than the obstacle? The following example illustrates how this question can be answered by the cost-effectiveness procedure.

Existing Hazard - No Protection

Assume that the existing hazard conditions are the same as those in Example 2 except that In- stead of three bridge piers the obstacles are three sma l l trees located on the roadside In- stead of the mod I an. A1 I of the psraeters defined under no protection of Example 2 there- f o r ~ apply here,' wIth one gtceptlon and that is the SI of the trees which Is assumed as 5.0. It will tm further assumed that the SI of the trees does not change over the 20-year perlod. Shoui d this not tm the case, the procedure presented herein would not be applicable. Selec- tlon of an S I for such obstacles must bs based primarily on engineering Judgment due to an absence of obJective criteria. Fran Figure 5.1.21 :

Thus,

and

Protection by Roadside Barrier

All of the parameters from the Example 2 Roadside Barrier Section apply here.

Thus, c -$10,726 *T

and

Comparison REFERESCES

Tha most cost-affectiva al ternat iva In t h i s cau 1. MSHTO, Guide For Se lec t i ng , L o c a t i n g I s t o leave tho treos unshlalded (assuming thay and Design ing T r a f f i c B a r r i e r s , 1977. cannot be removed) sinca tha numuator of th. ranklng equation "RN i s negative. Although t he 2. Heaver, Graeme D. and D.L. Woods. Cos t - trees would have a gea ta r hazard potential per E f fec t i veness E v a l u a t i o n o f Roadside S a f e t y accident, the considerably greater target area Improvements on Texas Highways. Research Report 15-2F, Texas T r a n s p o r t a t i o n I n s t i t u t e , of the barr ier and I t s closer proximity to tho 1 9 7 6 .

- - . -.

travaled way would resu l t In considerably nure barr ier impacts than trea Impacts. However, as tho length of tha I lne of trees Increases, the- d lffarence in the cost of the two al ternatlves decreases. A t sane length of unshie ldd trees the barr Ier w u l d becane m a cost e f fec t lve. The reader should also remenbe that the size of tha tree i s very slgnlglcant in t h i s analysis. Repeated solutlons S l m l la r to the one above for d i f fe ren t lengths of unshlelded trees w i l l rwea l the break-even point where tho barr ier

U. S. DEPARTMENT OF TRANSPORTATION b SUBJECT FHWA BULLETIN

A s a r e s u l t o f e n e r g y c o n s e r v a t i o n p o l i c i e s , e n v i r o n m e n t a l , economic, and o t h e r c o n c e r n s , p a s s e n g e r v e h i c l e s a r e becoming s m a l l e r and l i g h t e r . The highway d e s i g n s and d e c i s i o n s i n t h e f u t u r e can be r e s p o n s i v e t o t h i s chang ing v e h i c l e f l e e t a s _the FHWA w i l l now i n c l u d e t h e m i n i - s i z e d c a r a s a t e s t v e h i c l e I n j t s resc- . - : . , . w - . - . . . . -I .... 2 a t improvine roadway d e s i e n a n d r o a d s i d e s a f e t v .

FHWA Sponsored Research t o Now C o n s i d e r t h e Min i -S ized Car (1 ,700-1 ,800 pounds)

The FHWA i s a c t i v e l y p u r s u i n g , t h rough r e s e a r c h and development , t h e d e s i g n o f highway b a r r i e r sys tems ( i . e . , g u a r d r a i l s , b r i d g e r a i l s . , and median b a r r i e r s ) and s u p p o r t s f o r s i g n s , l u m i n a i r e s , and u t i l i t y p o l e s t h a t w i l l s a f e l y accommodate t h e a r r a y o f t h e s e newer v e h i c l e s . T h i s means t h e c r a s h t e s t i n g s t u d i e s t h a t have been s o s u c c e s s f u l i n t h e p a s t u s i n g 4 , 5 0 0 pound f u l l - s i z e c a r s and 2 , 2 5 0 pound compact c a r s , w i l l i n c l u d e from now on t h e 1 , 7 0 0 -

,800 pound m i n i - s i z e d c a r . his s m a l l e r s i z e c a r is p a r t i c u l a r 1 1 t m p o r t a n t i n t h e d e s i g n o$ breakaway o r y i e l d i n g s i g n s u p p o r t s and b a r r i e r georne t r i c s .

Apr i l 2 6 , 1979 *

I n i t i a l FHWA s p o n s o r e d r e s e a r c h w i t h m i n i - s i z e d c a r s h a s r e c e n t l y i n v o l v e d c r a s h t e s t i n g i n t o b r i d g e r a i l s and s m a l l s i g n s u p p o r t s . F o r f u t u r e . r e s e a r c h , t h e m i n i - s i z e d c a r w i l l be used t o p r o v i d e needed i n s i g h t i n t o t h e e f f e c t s o f t h e chang ing v e h i c l e f l e e t on t h e highway.

I n a d d i t i o n t o t h e m i n i - s i z e d c a r , FHWA is a l s o u s i n g s c h o o l b u s e s , i n t e r c i t y - b u s e s , and even t r a c t o r - t r a i l e r t r u c k s i n i t s r e s e a r c h t o d e t e r m i n e what i s needed a t t h e o t h e r end o f t h e s c a l e t o r e t a i n heavy v e h i c l e s i n c o l l i s i o n s w i t h highway b a r r i e r . s y s t e m s .

S e v e r a l s t u d i e s a r e underway and more a r e s c h e d u l e d t h a t s h o u l d p r o v i d e sound e v i d e n c e on which t o b a s e judgments on s e l e c t i n g and d e s i g n i n g highway s a f e t y a p p u r t e n a n c e s f o r v a r i o u s k i n d s o f highways.

$,Jg C7* Jcy G . O . Love

Xf&iJ H. L . Anderson

A s s o c i a t e A d m i n i s t r a t o r f o r A s s o c i a t e A d m i n i s t r a t o r f o r Resea rch and Development S a f e t y

o~s~u~euttou: H - WDM- 4 HHS - 1 2

CRASH CUSHION DESIGN CURVES

HI-DRO CELL

Design Speed-mph

HI-DRI CELL

- -

Design Speed-mph

Design Speed - mph

(?Av) ( HdW 1 013dS N I 39NVH3

'M - ('S011 ONVS JO lH913M

'YO.1.Y PIIS.lPY) so AU~IIU..~. W I P Y ~ ~ h ~ a n ~ i s u o a pus SIOIIOIOW 11s b~qslurn) rot WI -3 yll PWP1SW1 W WYS SUbl1 1).1lU03 101 p(p .*Id

swltmlnqol PU* rumy m y prspusls rw lo 01 lai*r SII~LP Pbm SluW.I!nb*l a111n4s m j .uww uroqs sm IS& 11r1pr8nb WI 60 qasq I.*I O*I q r.plnoqs ~ Y I 80 .Opa mq~ WO*) .dois 8.01 l *parod 01 urn14 SIW 10 I ~ O W WI st 81 WY~II$*O* ml umvs 41110d YIWU* '9 YOO~IPISY YI YO^( smILL\!p IIS'DAS~O ow 0 a m w sou* y

'1a.ulbu. .q1 lu u q i Y~IP WI I* 4 II~YS s~no lm~ osbq101 suollSal1IPQw Auv m~mo

*. .

SAMPLE GRAPHIC SOLUTION TO LENGTH OF NEED EQUATION RUNOUT LENGTH SCALE

" X " For Opposing T r a f f i c ConterIlnr 1 . a a a - - * a a l . . n a ' ~ m . a r l a a - L a * L I a . ' * t a ' * - I

Scale d 50' 100' 15d 200' 25d 300' 350' 400' 4%' 500' L R

.!! 32', z d , (L O 28' w

2d,

g 24 22'

t! 2d

EXAMPLE ---- Rrprrsrnts length of nard in front of hazard locotrd 18'from edge of povemmt when oprratlng sprrd Is 60mph, and drslgn lroff ic volumr (AbT)ls 5200 ,

STEPS =elect runout length L (page 64 o f B a r r i e r Guide). 2. Determine distabce frd edge o f pavement t o hazard

(L f i gu re 111-E-4 page 63 o f Ba r r i e r Guide). 3. ~rh a s t ra i gh t l i n e between L p lo t t ed on the

v e r t i c a l scale and LR p lo t t ed an the hor izonta l scale. ' 4. Nhere the l i n e drawn i n step 3 i n t v s e c t s the

hor izontal 1 ine representing the 1 )cat ion o f the b a r r i e r f r o m the pavement edge dra v a 1 i n e v e r t i c a l l y t o the hor izontal axis.

--- Rrprrsrntr length of nard in front of hozard undrr somr conditions uc rp t tho vrhlclr h opprooching from the opposite dirrction.

---- Rrprrsrnts Barrlrr locallon In rrloflon lo rdgr of povrmrnt.

5. Read so lu t ion o f " X u coordinate on LR ax is d i r e c t l y below the in te rsec t ing po in t .

NOTE: 12 f oo t lanes assumed.

, , , , , , , *

V, ul

--

'1 r . . . . ~ . . . . ' h . . . l .

s& 40d 450' :I

Barrlrr Location in Rrlotion to Ed91 of Povrmrnt

500' L R

I "Xu For Near Side Source: State o f I l l i n o i s

RUNOUT LENGTH SCALE

Location in Relal io~ to Edge o ' Pavrmrnt

34

so' I- ; 2e', ' 26' &L 0 24' I g 22' I& w 20' U z 18'

' 16' 5

I EXAMPLE --- Rrprrrrnts length of nrrd I n front of hazard locatrd 19 from rdg r o f povrmml

- when oprrating nprrd i s 70 mph, and d r r i gn I r o f f i c volumr (ADT) in 7000 . - -

--- Reprentntr L 3 , length to be omit t rd from length of need.

NOTE: 25' Solution END OF NEED FOR NEAR SIDE TRAFFIC only va l i d when STEPS

, opposing t r a f f i c 1. P lo t L distance - edge o f pavement t o hazard i s outside the distanze - on ver t i ca l axis (See page 63 o f clear zone Barr ier Guide) .

, 2. Draw a l i n e from thp po in t established i n step ,

1 a t an angle of 25 :n accordance w i th the gui del i ne given.

3. Where t h i s l i n e in ter : ects a horizontal l i n e ? \ plot ted a t the L d is l ance - the distance from \ the edge o f paveent 1, tiu bar r ie r - (See page \ 1 \ 63 o f Barr ier Guide) c raw a ver t ica l 1 ine to 1 the L axis.

---- Rrprrnrntr Barr i r r location In rotation to r d g r of pavrment.

\ 4 . Read !he value cf "Xu to the po in t where the 1 1 ba r r i e r i s no longer r 2eded. 25O

--

\ ---

I '\ x I 1 $ 4' I

I '1 2' 1 m 4 Ed9@cfpav0t L. f - ' \ . . I . . . . I . . a I n . a I ; . n I

Scale 0' " 50' 100' 150' 200 25 300' 350' 400 450' 3 m m 0 (0 NOTE: Barr ier length must be l"2. o increased f o r hazards ; ~ = l +, rD 3 fD 4.

Source: State o f I l l i n o i s other than po in t hazards

Z P J m ( i .e . , solut ion only va l i d a m P f o r po in t hazards)

CUT SLOPE (b,/oz) FILL SLOPE ( bl/al )

CUT SLOPE (RECIPROCAL)

FlLL SLOE (RECIPROCAL)

E z 0 > U L 3co V) Urn aJ SEg ?eta >+ n

CLEAR ZONE REQUIREMENTS

F O R DEGREE OF CURVE :

4 FILL SECTION

b

CUT SECTION

L SPEED I

34

29

31

33

85

93

101

163

177

, 182

VOL. 800- 2000 2000-

104

22

23

6:1

25

26

28

35

34

23

26

27

32

84

22

23

64 22

23

3: 1 22

10:l

22

23 40MPH

2000- 50MPH 30 33 35 35 35 35 35 35 38 44

5:J

26

28

25

32

25

32

4:l 22

6000 1 23 .-. 23

52

30

40

4:l

28

29

5:l 22

23

32

48

6000+ 800-

25

30

25

32

25

36 38 38 38 38 38 38 42 47 -

60

35 44 46 48 50 51 55 56 58 65

70

25

32

25

32

57

73

79

- 84

t 2000 27

FOR DEGREE OF CURVE :

CLEAR ZONE REQUIREMENTS,



FOR DEGREE OF CURVE

I

I CUT SECTION I FILL SECTION I

CLEAR ZONE REQUIREMENTS F O R DEGREE O F CURVE :

I CUT SECTION FILL SECTION 10:l 0 : 8:l

I

SPEED 3:1 5:l 5:1 8:l - + * + + i + , + + 4 * + + * * * ' * + " '

+ 8 4

97'

110'

267'

3 1 6 ~ : b

3 7 2 ' .

523

593

699

4:l

'6;

73

83

100

118

139

147

167

197.

6:l 1

6:l + %A

88

100

125

147

l V 5 3 1 7 4

193

219

- . 250

40MPH

50MPH

I

VOL. '76

92

105

150

177

208

235

267

- 315

' 6 ' 3 ' sj 73

83

100

118

139

136

155

l83>

+;7*

70

89

100

118

139

167

189

- 223

73

83

Q3"'&

73

83

100

118

139

141

160

j89 -

800- ., 2000 + 2000- + + 6000

-

3: 1 ' 7 i

83

94

110

130

173

196

- 231.

73

683

4:l * - + + * + i t

148

1 7 4

i3* + * 7 3

b

1 0 0 4

118

139

152

173

, -204

2000- * 60MPH ,,,, 6000-5 :

t 6 j 73

100

118

139

162

183

- 216

C

+'I18 7

' 1 ~ 9 ~ ~ -

83

95

112

132

130

6 0 0 b + : ~ 8 3

+ * ' + t + * t t + t ' * ~ * + + * ' + + t ' t ' t + t + +

800- * ' 2000 + + 2000- 4 - 6000 6000+: '118

800- 2000

85

. ' l oo ..

* '

+'I04



I I CUT SECTION I FILL SECTION I

GUIDELINES FOR DETERMINING GUARDRAIL NEED, LOCATION AND STANDARDS Source: State o f Georgla

CONTENTS

I. GUARDRAIL WARRANTY FOR FILL EMBANKMENT

I I. GUARDRAIL WARRANTY FOR ROADSIDE OBSTACLES

1. Nontraversabl e Hazards

2. Fixed Objects 3. Clear Zone Width

111. LFMCTU OF hlFtn

I V . GUARDRAIL LOCATION

1. Guardrai l Located On the Graded Shoulder

2. Guardrai l Located Back o f t he Graded Shoulder

3. Roadside Obstacles

4. Bridge Approaches

5. Guardrai l Located Back o f Curb

V. CHART FOR SELECTED GUARDRAIL STANDARDS

. Revised: 11-9-77 - RMU Revised: 9-25-78- RMU Revised: 11-8-79 - RMU Revised: 2-14-80 - RMU NOTE: This mater ia l i s provided

f o r the readers use only. I t does n o t cons t i t u te a p o l i c y o m h e Federal Highway Administrat ion.

I. GUARDRAIL WARRANTY FOR FILL EMBA-

Height and slope o f roadway embankment are basic factors i n determining guardrai l need. I n Figure 1 (A) below, an extrapolation o f fill height and slope which f a l l s above o r t o the r i g h t of the curve indicates an embankment hazard of a greater sever i ty than the guardrai l . A slope and height combf- nat ion which f a l l s below the curve indicates an embankment which i s less severe than the guardrai l . Guardrail should not be used f o r embankment protect ion i f the slope height extrapolat ion f a l l s on o r below the curve, however other condit ions such as f i xed hazards, length o f advancement, etc. may warrant guardrai l .

WHERE FEASIBLE, THE FLATTENING OF WARRANTING SLOPES I S PREFERRABLE TO REQUIRING GUARDRAIL .

The warranty c r i t e r i a shown i n Figure 1 (A) i s intended p r imar i l y f o r higher t r a f f i c volume and higher speed design r u r a l type roads. I n general, i t i s not cost -ef fect ive t o require guardrai l on the lower t r a f f i c volume

(continued on Page -2-)

FIGURE NO.

barandas segun aashto

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