3_tr 320_road functional classification
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8/3/2019 3_TR 320_Road Functional Classification
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TR 320: Road FunctionalTR 320: Road Functional
Classification and DesignClassification and DesignControls and CriteriaControls and Criteria
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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
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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
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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
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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
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Major Rd Classes…Major Rd Classes…
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)
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Major Rd Classes…Major Rd Classes…
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
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Major Rd Classes…Major Rd Classes…
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
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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.
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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
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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?)
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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)
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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
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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
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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
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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.
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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
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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
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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.”
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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)
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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)
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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
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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
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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
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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.
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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)
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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)
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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.