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Ward Planning and Education Secretaries · Chapter 7

Traffic and Transportation

What to remember

  • Traffic engineering uses three basic measures: flow (vehicles per hour), density (vehicles per km) and speed (km per hour), linked by the formula flow = density x speed.
  • Roads are classified by function: national and state highways, major and other district roads, village roads outside towns; arterial, sub-arterial, collector and local streets inside towns.
  • Good urban transport moves people, not just vehicles: public transport, walking and cycling are planned first, together with parking, junction design and road safety.

1. Road classification

Outside towns (Nagpur Road Plan, 1943)

ClassRole
National Highways (NH)Join states, ports and big cities; built and kept by the Centre
State Highways (SH)Join district headquarters and important towns within a state
Major District Roads (MDR)Join production and market areas to highways
Other District Roads (ODR)Join smaller areas to MDR
Village Roads (VR)Join villages to each other and to higher roads

An expressway is a divided highway with controlled access and no crossing at the same level.

Inside towns (functional classification)

ClassFunction
ArterialCarries heavy through traffic across the city; fewest access points
Sub-arterialLinks arterials, serves long local trips
CollectorCollects traffic from local streets and feeds arterials
Local streetGives access to homes and shops; low speed

Roads should have footpaths, cycle lanes where possible, drains, street lights and trees. A footpath should be clear and wide enough for people to walk, often about 1.5 m at least.

2. Basic traffic measures

MeasureMeaningUnit
Volume (flow, q)Number of vehicles passing a point in unit timevehicles per hour
Density (k)Number of vehicles in unit length of roadvehicles per km
Speed (v)Distance travelled per unit timekm per hour
HeadwayTime gap between two vehicles at a pointseconds
CapacityMaximum flow a road can carry under given conditionsvehicles or PCU per hour
Passenger Car Unit (PCU)Converts different vehicles into car equivalentsCar = 1

Basic relation: flow q = density k x speed v. At zero density there is no flow; at jam density speed is zero. Flow is highest at a middle density, which is the capacity.

Headway: average headway (s) = 3600 / flow (vehicles per hour).

Peak Hour Factor (PHF) = hourly volume / (4 x volume in the busiest 15 minutes). It is always 1 or less.

PCU. A car is taken as 1. A two-wheeler is less than 1 (often 0.5) and buses and trucks are more (often 2 to 3 or more), because they take more road space. In problems the values are given.

Level of Service (LOS) grades road operation from A (free flow) to F (forced, jammed flow).

Worked example 1. Density 40 vehicles per km and speed 30 km per h. Flow = 40 x 30 = 1,200 vehicles per hour. Headway = 3600 / 1200 = 3 s.

Worked example 2. Hourly volume 1,200 vehicles and the busiest 15 minutes has 360 vehicles. PHF = 1200 / (4 x 360) = 0.83.

Worked example 3. Count in an hour: 100 cars (1.0), 50 two-wheelers (0.5) and 10 buses (3.0). Total PCU = 100 + 25 + 30 = 155 PCU per hour.

Speed conversion. Km per hour divided by 3.6 gives metres per second. 72 km per h = 20 m per s.

3. Traffic surveys

  • Volume count: manual or automatic; gives peak hour and daily flow.
  • Speed and delay study: spot speed and journey time.
  • Origin-Destination (O-D) survey: where trips start and end.
  • Parking survey: accumulation, duration, turnover.
  • Accident study: identify black spots (places with repeated crashes).

4. Geometric design basics

Sight distance is the length of road ahead that a driver can see. Stopping Sight Distance (SSD) = distance in reaction time + braking distance.

SSD = v x t + v squared / (2 g f), where v is speed in m per s, t is reaction time (s), g = 9.81 m per s squared (10 for easy calculation) and f is the coefficient of friction.

Worked example 4. V = 72 km per h = 20 m per s, t = 2.5 s, f = 0.4, g = 10. SSD = 20 x 2.5 + 400 / (2 x 10 x 0.4) = 50 + 50 = 100 m.

Superelevation (banking) on curves: e + f = v squared / (g R), where R is the radius of the curve.

Worked example 5. v = 10 m per s, R = 50 m, g = 10 m per s squared, f = 0.15. e + f = 100 / 500 = 0.2, so e = 0.2 - 0.15 = 0.05 (5 in 100).

Camber is the cross slope of a road that drains rain to the sides. Gradient is the rise or fall along the road.

5. Junctions

  • At-grade junctions: T, Y, four-leg crossing, roundabout (rotary), signalised junction.
  • Grade-separated junctions: flyover, underpass, interchange. They remove crossing conflicts but cost more.
  • A four-leg two-way crossing has 32 conflict points; a three-leg two-way junction has 9. Roundabouts and signals reduce conflicts.

Traffic signals. Time is split among the phases. Webster's formula for the optimum cycle time: C = (1.5 L + 5) / (1 - Y), where L is total lost time per cycle (s) and Y is the sum of the critical flow ratios.

Worked example 6. L = 10 s and Y = 0.5. C = (15 + 5) / 0.5 = 40 s.

Traffic signs: mandatory (regulatory) signs are circular, cautionary (warning) signs are triangular, and informatory signs are rectangular.

6. Parking

  • On-street parking reduces road capacity; it is priced or limited.
  • Off-street parking is in lots or multi-level structures.
  • Parking turnover = number of vehicles parked in a period / number of parking bays.
  • Park-and-ride lots near transit stations reduce traffic in the centre.

Worked example 7. 120 vehicles park in 20 bays in a day. Turnover = 120 / 20 = 6 vehicles per bay per day.

7. Urban transport planning

Four-stage model: trip generation (how many trips) then trip distribution (where they go) then modal split (which mode) then trip assignment (which route).

National Urban Transport Policy (2006) says to move people rather than vehicles, to support public transport and to encourage walking and cycling. Cities make a Comprehensive Mobility Plan. Transit-Oriented Development (TOD) puts homes, jobs and shops near high-quality transit stations.

ModeNotes
City busBackbone of most Indian cities; operated by the state road transport undertaking, in AP by APSRTC
Bus Rapid Transit (BRT)Bus on a dedicated lane; cheaper than rail. Vijayawada and Visakhapatnam have had BRT corridors
Metro rail (MRTS)High capacity, built in big cities; metro proposals in AP cities should be checked for latest status
Suburban railUses existing rail lines
Intermediate public transportAutos and shared vans
Non-motorised transportWalking, cycling, which are clean and cheap

8. Road safety

The four E's are Engineering, Enforcement, Education and Emergency care. The Motor Vehicles Act, 1988 (amended in 2019) regulates licences, registration, rules of the road and penalties. Common measures are helmets and seat belts, speed limits, zebra crossings, pedestrian refuges, rumble strips, street lights, and fixing black spots.

Exam traps

  • Flow is vehicles per hour; density is vehicles per km; do not mix them.
  • PHF is never more than 1.
  • Arterial roads carry through traffic; local streets give access.
  • Nagpur plan classes (NH, SH, MDR, ODR, VR) apply outside towns.
  • SSD includes both reaction distance and braking distance.
  • A flyover separates crossing at different levels; a roundabout is still at grade.
  • Mandatory signs are circular; warning signs are triangular.
  • BRT is bus on a dedicated lane; it is not a rail system.

One-liners

  • 1. Flow = density x speed.
  • 2. Headway in seconds = 3600 / flow per hour.
  • 3. 1 PCU is the value of one car.
  • 4. LOS runs from A (best) to F (worst).
  • 5. The Nagpur Road Plan is dated 1943.
  • 6. A four-leg two-way crossing has 32 conflict points.
  • 7. A three-leg two-way junction has 9 conflict points.
  • 8. Webster's formula: C = (1.5 L + 5) / (1 - Y).
  • 9. Speed in m per s = km per h / 3.6.
  • 10. NUTP (2006) stresses moving people, not vehicles.
  • 11. The four E's of road safety are Engineering, Enforcement, Education and Emergency care.
  • 12. The Motor Vehicles Act is from 1988.

Practice questions

  1. Which formula connects the basic traffic flow variables?

    1. flow = density / speed
    2. flow = density x speed
    3. flow = speed - density
    4. flow = density + speed
    Answer

    B. flow = density x speed

    q = k x v.

  2. Density of traffic is measured in

    1. km per hour
    2. seconds per vehicle
    3. vehicles per hour
    4. vehicles per km
    Answer

    D. vehicles per km

    Density is vehicles per unit length.

  3. Traffic density is 50 vehicles per km and average speed is 40 km per h. The flow is

    1. 90 vehicles per hour
    2. 2,000 vehicles per hour
    3. 1.25 vehicles per hour
    4. 200 vehicles per hour
    Answer

    B. 2,000 vehicles per hour

    50 x 40 = 2,000.

  4. The flow on a lane is 1,800 vehicles per hour. The average headway is

    1. 18 s
    2. 0.5 s
    3. 2 s
    4. 5 s
    Answer

    C. 2 s

    3600 / 1800 = 2 s.

  5. The flow on a lane is 900 vehicles per hour. The average headway is

    1. 9 s
    2. 2 s
    3. 0.25 s
    4. 4 s
    Answer

    D. 4 s

    3600 / 900 = 4 s.

  6. Peak hour factor (PHF) is the ratio of hourly volume to

    1. the daily volume
    2. 4 times the busiest 15-minute volume
    3. the busiest minute volume
    4. the average hourly volume
    Answer

    B. 4 times the busiest 15-minute volume

    PHF = V / (4 x V15).

  7. The hourly volume is 800 vehicles and the busiest 15-minute volume is 250. The PHF is

    1. 0.31
    2. 1.25
    3. 3.2
    4. 0.8
    Answer

    D. 0.8

    800 / 1000 = 0.8.

  8. In an hour the count is 80 cars (1.0), 40 two-wheelers (0.5) and 5 buses (3.0). The total PCU is

    1. 115
    2. 150
    3. 125
    4. 85
    Answer

    A. 115

    80 + 20 + 15 = 115.

  9. The value of PCU for a car is taken as

    1. 1
    2. 0.5
    3. 2
    4. 3
    Answer

    A. 1

    Car is the standard unit.

  10. A speed of 90 km per h is equal to

    1. 90 m per s
    2. 25 m per s
    3. 250 m per s
    4. 32.4 m per s
    Answer

    B. 25 m per s

    90 / 3.6 = 25.

  11. Level of Service A means

    1. forced jammed flow
    2. capacity flow
    3. free flow with high comfort
    4. unstable flow only
    Answer

    C. free flow with high comfort

    A is best; F is worst.

  12. The Nagpur Road Plan classified roads outside towns into

    1. freeway and tollway
    2. single and double lane roads
    3. arterial, collector and local
    4. NH, SH, MDR, ODR and VR
    Answer

    D. NH, SH, MDR, ODR and VR

    The five classes of the Nagpur plan.

  13. The Nagpur Road Plan is of the year

    1. 1956
    2. 1943
    3. 1920
    4. 1991
    Answer

    B. 1943

    The Nagpur Road Plan of 1943.

  14. National Highways mainly

    1. serve only single villages
    2. join states, ports and big cities
    3. are used only inside a ward
    4. give access to individual houses
    Answer

    B. join states, ports and big cities

    NH form the main backbone of roads.

  15. Which urban road class carries heavy through traffic with the fewest access points?

    1. Local street
    2. Collector street
    3. Arterial road
    4. Service lane
    Answer

    C. Arterial road

    Arterials carry through traffic.

  16. Which urban road class mainly gives access to homes and shops?

    1. Sub-arterial road
    2. Expressway
    3. Local street
    4. Arterial road
    Answer

    C. Local street

    Local streets give access at low speed.

  17. Stopping Sight Distance is the sum of

    1. camber and superelevation
    2. road width and gradient
    3. braking distance and overtaking distance
    4. reaction distance and braking distance
    Answer

    D. reaction distance and braking distance

    SSD = vt + v squared / 2gf.

  18. A car moves at 20 m per s with reaction time 2 s and brakes with v squared / (2 g f) = 50 m. The SSD is

    1. 90 m
    2. 50 m
    3. 40 m
    4. 110 m
    Answer

    A. 90 m

    20 x 2 = 40 m; 40 + 50 = 90 m.

  19. Speed 72 km per h, reaction time 2.5 s, f = 0.4, g = 10. The SSD is

    1. 75 m
    2. 100 m
    3. 50 m
    4. 150 m
    Answer

    B. 100 m

    50 + 400 / 8 = 100 m.

  20. The relation for superelevation on a horizontal curve is

    1. e + f = v squared / (g R)
    2. e + f = g R / v squared
    3. e - f = v / R
    4. e x f = v squared
    Answer

    A. e + f = v squared / (g R)

    Standard formula for curves.

  21. A curve of radius 50 m, speed 10 m per s, g = 10 and f = 0.15. The superelevation e is

    1. 0.2
    2. 0.35
    3. 0.05
    4. 0.15
    Answer

    C. 0.05

    e + f = 100/500 = 0.2; e = 0.05.

  22. The cross slope of a road that drains rain to the sides is called

    1. superelevation
    2. kerb
    3. gradient
    4. camber
    Answer

    D. camber

    Camber is cross slope.

  23. A four-leg two-way crossing has how many conflict points?

    1. 9
    2. 64
    3. 32
    4. 16
    Answer

    C. 32

    A crossing has 32; a three-leg junction has 9.

  24. A three-leg two-way junction has how many conflict points?

    1. 3
    2. 18
    3. 32
    4. 9
    Answer

    D. 9

    Three-leg junction: 9 conflict points.

  25. Webster's formula for optimum signal cycle time is

    1. C = (1.5 L + 5) / (1 - Y)
    2. C = (L + Y) / 2
    3. C = 1.5 L / Y
    4. C = L x Y
    Answer

    A. C = (1.5 L + 5) / (1 - Y)

    L = lost time; Y = sum of critical flow ratios.

  26. With L = 12 s and Y = 0.6, Webster's optimum cycle time is

    1. 30 s
    2. 58 s
    3. 115 s
    4. 48 s
    Answer

    B. 58 s

    (18 + 5) / 0.4 = 57.5, about 58 s.

  27. With L = 10 s and Y = 0.5, Webster's optimum cycle time is

    1. 20 s
    2. 60 s
    3. 30 s
    4. 40 s
    Answer

    D. 40 s

    (15 + 5) / 0.5 = 40 s.

  28. Parking turnover is the

    1. width of a parking bay
    2. fee charged per hour
    3. number of vehicles parked in a period divided by number of bays
    4. time a car stays in a bay
    Answer

    C. number of vehicles parked in a period divided by number of bays

    Turnover = vehicles / bays.

  29. 120 vehicles use 30 parking bays in a day. The turnover is

    1. 4 vehicles per bay
    2. 0.25
    3. 90
    4. 150
    Answer

    A. 4 vehicles per bay

    120 / 30 = 4.

  30. A flyover is an example of a

    1. roundabout
    2. grade-separated junction
    3. zebra crossing
    4. at-grade crossing
    Answer

    B. grade-separated junction

    It separates crossing movements at different levels.

  31. Mandatory (regulatory) road signs are generally

    1. triangular
    2. rectangular only
    3. circular
    4. hexagonal only
    Answer

    C. circular

    Mandatory signs are circular.

  32. The first of the four stages in the urban transport model is

    1. modal split
    2. trip generation
    3. trip distribution
    4. trip assignment
    Answer

    B. trip generation

    Order: generation, distribution, modal split, assignment.

  33. Which stage of the four-stage model decides which travel mode people use?

    1. Trip generation
    2. Trip assignment
    3. Trip distribution
    4. Modal split
    Answer

    D. Modal split

    Modal split chooses the mode.

  34. Consider the statements. 1. Peak hour factor is never more than 1. 2. PCU converts different vehicles into car equivalents. Which is/are correct?

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    C. Both 1 and 2

    Both are correct.

  35. Consider the statements. 1. Arterial roads give access to individual houses. 2. Local streets carry heavy through traffic. Which is/are correct?

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    D. Neither 1 nor 2

    Arterials carry through traffic; local streets give access.

  36. Consider the statements. 1. A flyover removes crossing conflicts by separating levels. 2. A roundabout is a grade-separated junction. Which is/are correct?

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    A. 1 only

    A roundabout is an at-grade junction.

  37. Consider the statements. 1. National Urban Transport Policy stresses moving people, not vehicles. 2. BRT uses a dedicated bus lane. Which is/are correct?

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    C. Both 1 and 2

    Both statements are correct.

  38. Consider the statements. 1. Headway in seconds = 3600 / flow per hour. 2. Flow is measured in vehicles per km. Which is/are correct?

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    A. 1 only

    Flow is vehicles per hour; density is vehicles per km.

  39. Consider the statements. 1. SSD includes the distance covered during reaction time. 2. SSD includes the braking distance. Which is/are correct?

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    C. Both 1 and 2

    SSD adds reaction and braking distances.

  40. Consider the statements. 1. The Motor Vehicles Act is from 1988. 2. The four E's of road safety include Engineering and Enforcement. Which is/are correct?

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    C. Both 1 and 2

    Both statements are correct.

  41. Match the item with its meaning. P. Density Q. Flow R. Headway 1. Vehicles per hour 2. Seconds between vehicles 3. Vehicles per km

    1. P-1, Q-3, R-2
    2. P-3, Q-1, R-2
    3. P-2, Q-1, R-3
    4. P-3, Q-2, R-1
    Answer

    B. P-3, Q-1, R-2

    Density per km; flow per hour; headway in seconds.

  42. Match the sign shape with its type. P. Circular Q. Triangular R. Rectangular 1. Informatory 2. Mandatory 3. Cautionary

    1. P-2, Q-3, R-1
    2. P-2, Q-1, R-3
    3. P-3, Q-1, R-2
    4. P-1, Q-2, R-3
    Answer

    A. P-2, Q-3, R-1

    Circular = mandatory; triangular = cautionary; rectangular = informatory.

  43. Match the road class with its role. P. NH Q. SH R. VR 1. Join villages 2. Join states and ports 3. Join district headquarters within a state

    1. P-1, Q-3, R-2
    2. P-3, Q-2, R-1
    3. P-2, Q-1, R-3
    4. P-2, Q-3, R-1
    Answer

    D. P-2, Q-3, R-1

    NH join states and ports; SH join district HQs; VR join villages.

  44. The four E's of road safety are Engineering, Enforcement, Education and

    1. Economy
    2. Emergency care
    3. Employment
    4. Electrification
    Answer

    B. Emergency care

    The fourth E is Emergency care.

  45. Park-and-ride facilities are built mainly to

    1. remove footpaths
    2. increase on-street parking
    3. raise the speed of heavy trucks
    4. reduce traffic in the central area by shifting people to transit
    Answer

    D. reduce traffic in the central area by shifting people to transit

    They link parking with public transport.

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