3_tr 320_road functional classification

8/3/2019 3_TR 320_Road Functional Classification

http://slidepdf.com/reader/full/3tr-320road-functional-classification 1/29

11

TR 320: Road FunctionalTR 320: Road Functional

Classification and DesignClassification and DesignControls and CriteriaControls and Criteria



22

Road FunctionsRoad Functions

Mobility: Movement from one place toMobility: Movement from one place to

anotheranother High Speed (usually high traffic volume)High Speed (usually high traffic volume)

Access: Provides for access to properties Access: Provides for access to properties

Mixed function: both movement andMixed function: both movement and

access functionsaccess functions



33

Recap – From TR 210Recap – From TR 210

What are the functions of the followingWhat are the functions of the following

roads?roads? Uvumbuzi RdUvumbuzi Rd University RdUniversity Rd

Sam Nujoma RdSam Nujoma Rd

Morogoro RdMorogoro Rd Shekilango RdShekilango Rd



44

2. Major Rd Classes2. Major Rd Classes

Arterial Rd Arterial Rd Major roads linking national and internationalMajor roads linking national and international

centrescentres Provides for mobility from one urban centreProvides for mobility from one urban centre

and another (and within urban centres)and another (and within urban centres)

High speed, long trip lengthHigh speed, long trip length High volume and therefore geometric designHigh volume and therefore geometric design

standards must be high to enable efficientstandards must be high to enable efficient

traffic operationtraffic operation



55

Major Rd Classes…Major Rd Classes…

Arterial Rd – Design types Arterial Rd – Design types FreewaysFreeways

Dual carriagewaysDual carriageways Multilane roadways (without medians)Multilane roadways (without medians) Two-lane two-way roadwaysTwo-lane two-way roadways

Access to the roadway varies: very Access to the roadway varies: veryrestricted for the freeways/principalrestricted for the freeways/principalarterials but less restricted for two-lanearterials but less restricted for two-laneroadwaysroadways



66


Collectors / DistributorsCollectors / Distributors Links traffic from and to rural areas to theLinks traffic from and to rural areas to the

major arterial roads or urban centresmajor arterial roads or urban centres Many of these also provides access toMany of these also provides access to

individual propertiesindividual properties

(Provides both mobility and access – mixed(Provides both mobility and access – mixedfunction)function)




Collectors / DistributorsCollectors / Distributors Traffic flow and trip length : intermediate levelTraffic flow and trip length : intermediate level

Need for high geometric standards is lessNeed for high geometric standards is lessimportantimportant

Design types: usually two-lane two-wayDesign types: usually two-lane two-way

roadwaysroadways



88


Access Rds Access Rds Are the lowest level in road network hierarchy Are the lowest level in road network hierarchy

Links to collector roadsLinks to collector roads Traffic volume very low, NMT often theTraffic volume very low, NMT often the

dominating modedominating mode

Access is primary function Access is primary function Design standards – low, just enough for theDesign standards – low, just enough for the

access functionaccess function



99

3. Design Controls/Standards3. Design Controls/Standards

A basic task for each road project is A basic task for each road project is

the selection design standardsthe selection design standardsthat match the environment,that match the environment,

needs and the desired level of needs and the desired level of

service.service.



1010

3.1Considerations3.1Considerations Design standards are selected so as toDesign standards are selected so as to

provide a desired level of service for theprovide a desired level of service for the

expected traffic volume and composition.expected traffic volume and composition.

The selection of the standards is governedThe selection of the standards is governedby the highway type (function) and theby the highway type (function) and the

characteristics of the location.characteristics of the location.

The selection of the standards is done atThe selection of the standards is done atthe beginning of the design processthe beginning of the design process



1111

Example: See Table 1.1 ORN #6Example: See Table 1.1 ORN #6

For a Typical bitumen standard Trunk For a Typical bitumen standard Trunk Road in Tanzania with ADT 400 to 1000Road in Tanzania with ADT 400 to 1000vpd located in rural flat terrain:vpd located in rural flat terrain: Design speed 100 – 120 km/hrDesign speed 100 – 120 km/hr Minimum curve radius - 500 mMinimum curve radius - 500 m Maximum superelevation 8 - 10%Maximum superelevation 8 - 10% Minimum curve length (aesthetics)?Minimum curve length (aesthetics)?

Lane width 2.75 - 3.25 m?Lane width 2.75 - 3.25 m? Camber 2.5%Camber 2.5% Maximum gradient 6 %Maximum gradient 6 %

Shoulder width 1 – 2 m (paved or gravel?)Shoulder width 1 – 2 m (paved or gravel?)



1212

3.2. Design controls/Factors3.2. Design controls/Factors

influencing designinfluencing design

i.i. Functional classificationFunctional classification

ii.ii. Traffic volume and mixTraffic volume and mixiii.iii. Design speedDesign speed

iv.iv. TerrainTerrain

v.v. Land use (Urban/rural)Land use (Urban/rural)



1313

Other factorsOther factors

i.i. LoS desiredLoS desired

ii.ii. Funds availableFunds availableiii.iii. Safety considerationsSafety considerations

iv.iv.

Social and environmental factorsSocial and environmental factors



1414

Critical factorsCritical factors

Desired LoSDesired LoS

Design vehicleDesign vehicle Design SpeedDesign Speed

Traffic VolumeTraffic Volume Plus driver, vehicle and roadPlus driver, vehicle and road

characteristicscharacteristics



1515

3.3. DESIGN HOUR VOLUME3.3. DESIGN HOUR VOLUME

DHV = projected hourly volume usedDHV = projected hourly volume used

for designfor design

Usually taken as a percentage of theUsually taken as a percentage of the

expected ADTexpected ADT

It has been shown that it isIt has been shown that it iseconomical to use the 30economical to use the 30thth highesthighest

hour volume (30 HV) as DHVhour volume (30 HV) as DHV

It is usually 12 to 18 percent of ADTIt is usually 12 to 18 percent of ADT



1616

DESIGN HOUR VOLUME …DESIGN HOUR VOLUME …

15% of ADT is used as average in15% of ADT is used as average in

rural areas.rural areas.

In urban areas DHV is 8% to 12% of In urban areas DHV is 8% to 12% of

ADT. Actual value depends on ADT. Actual value depends on

development density.development density. Directional distribution is important inDirectional distribution is important in

the determination of number of lanes.the determination of number of lanes.



1717

Composition of TrafficComposition of Traffic

Operating characteristics of vehicles areOperating characteristics of vehicles are

dependent on size and weightdependent on size and weight

Trucks are slower and occupy moreTrucks are slower and occupy moreroadway spaceroadway space

Effect on traffic operation of one truck isEffect on traffic operation of one truck is

equivalent to several passenger cars,equivalent to several passenger cars,actual equivalence being dependent onactual equivalence being dependent on

gradient, available PSDgradient, available PSD



1818

Composition of TrafficComposition of Traffic

The higher the proportion of trucks, theThe higher the proportion of trucks, the

greater the equivalent traffic demand andgreater the equivalent traffic demand and

the greater the highway capacity needed.the greater the highway capacity needed. For rural uninterrupted flow conditionsFor rural uninterrupted flow conditions

vehicles can be grouped into two majorvehicles can be grouped into two major

classes:classes: Passenger carsPassenger cars

Trucks – including all busesTrucks – including all buses



1919

3.4. Design Speed (DS)3.4. Design Speed (DS)

Definition - the “maximum safeDefinition - the “maximum safe

speed that can can be maintainedspeed that can can be maintainedover a specified section of over a specified section of

highway when conditions are sohighway when conditions are so

favourable such that the designfavourable such that the designfeatures of the highway govern.” features of the highway govern.”



2020

Factors affecting design speedFactors affecting design speed

Highway type (Function, designHighway type (Function, design

type, paved/unpaved)type, paved/unpaved) Terrain of the locationTerrain of the location

Land-use of the adjacent areaLand-use of the adjacent area

(density of development)(density of development)



2121

Factors affecting design speedFactors affecting design speed

And also we must consider And also we must consider

Trip length on the sectionTrip length on the sectionDriver expectation (e.g. for collectorDriver expectation (e.g. for collector

road in a flat terrain, mountainousroad in a flat terrain, mountainous

terrain = lower design speedterrain = lower design speedacceptable)acceptable)



2222

3.5. Design Vehicle3.5. Design Vehicle

Definition – that vehicle selectedDefinition – that vehicle selected

to represent all vehicles expectedto represent all vehicles expected

to use the roadway.to use the roadway.

Its dimensions and operatingIts dimensions and operating

characteristics are used tocharacteristics are used toestablish geometric standardsestablish geometric standards

((turning radii at inter., heightturning radii at inter., height



2323

cont.cont.

Design vehicle is the largest that isDesign vehicle is the largest that islikely to use the roadway withlikely to use the roadway with

considerable frequencyconsiderable frequency Restriction! Larger vehicles mayRestriction! Larger vehicles may

require permit before they can use therequire permit before they can use the

roadwayroadway Note: Increasingly larger vehiclesNote: Increasingly larger vehicles

being manufacturedbeing manufactured



2424

Typical Design VehiclesTypical Design Vehicles Passenger car – PPassenger car – P Single unit truck – SUSingle unit truck – SU

Single unit bus - BUSSingle unit bus - BUS Semi trailer – WB 40 or WB 50Semi trailer – WB 40 or WB 50

(Large)(Large) Full trailer – WB 50Full trailer – WB 50

Check text for detailsCheck text for details



2525

Maximum vehicle dimensions andMaximum vehicle dimensions and

weight limitsweight limits Countries or trading blocks specifyCountries or trading blocks specifymaximum dimensions, axle load andmaximum dimensions, axle load andGVW for vehicles that may be used onGVW for vehicles that may be used on

public roads.public roads. Designer must take account of theseDesigner must take account of these

restrictions.restrictions.

These vary with time as vehicleThese vary with time as vehicletechnology and economies develop.technology and economies develop.



2626

Assignment No. 3 Assignment No. 3

Compile maximum vehicle and weight limits forCompile maximum vehicle and weight limits forTrunk roads in Tanzania. (Mr. Yoel SamwelTrunk roads in Tanzania. (Mr. Yoel SamwelCSE)CSE)

Compile/select design vehicle and designCompile/select design vehicle and designstandards for the following roads:standards for the following roads:

i.i. Sam Nujoma Road (Mr. Aron Bahati CTE)Sam Nujoma Road (Mr. Aron Bahati CTE)

ii.ii. University Rd (UDSM) (Ms Hidaya Abbas –University Rd (UDSM) (Ms Hidaya Abbas –CSE)CSE)

iii.iii. DSM/Bagamoyo Rd (say 1200 vpd, flat terrain)DSM/Bagamoyo Rd (say 1200 vpd, flat terrain)

iv.iv. (Ms Sayi Kapera CWR)(Ms Sayi Kapera CWR)



2727

Tutorial 1Tutorial 1

Road project cross section design:Road project cross section design:

To determine number of lanesTo determine number of lanesand cross section detailsand cross section details

Projected AADT is 45000 vpdProjected AADT is 45000 vpd

Traffic composition 13% trucksTraffic composition 13% trucksand buses (1 truck = 2.6and buses (1 truck = 2.6passenger cars)passenger cars)



2828

Tutorial 1 …Tutorial 1 …

Road project cross section design:Road project cross section design: Desired level of service say 1100Desired level of service say 1100

passenger cars per lane per hour.passenger cars per lane per hour. Determine required ROW if desirableDetermine required ROW if desirable

median width is 12.0 m, NMY median width is 12.0 m, NMY

pavement 2.5 m wide and ditch areapavement 2.5 m wide and ditch areais 6.0 m.is 6.0 m.



2929

Determine number of lanes and proposeDetermine number of lanes and propose

cross section designcross section design

3_tr 320_road functional classification

Documents