TRAFFIC ENGINEERING EXAM QUESTIONS AND ANSWERS
Flow (Volume) definition - CORRECT ANSWER✅✅Average number of vehicles passing a given point per
unit of time
Flow (volume) Equation - CORRECT ANSWER✅✅q = N/T
(N is number of vehicles)
(T is duration of time interval)
UNITS: Vehicles/hour (urban) Vehicles/day (rural)
Pcu - CORRECT ANSWER✅✅passenger car unit
What is Pcu used for - CORRECT ANSWER✅✅To calculate traffic flow across signalised junctions
Journey speed (definition) - CORRECT ANSWER✅✅(Overall travel speed) is the average speed of a
vehicle on a journey, including involuntary stops
Journey speed (equation) - CORRECT ANSWER✅✅Vj = distance travelled/ journey time
Running speed - CORRECT ANSWER✅✅Vr, as for journey speed but excluding stops
Spot speed - CORRECT ANSWER✅✅Vi , is the speed of an individual vehicle measured instantaneously
at a given point, e.g. by radar.
Time Mean speed (definition) - CORRECT ANSWER✅✅The average spot speed of all the vehicles passing
a given point during a period of time.
Space Mean Speed (Definition) - CORRECT ANSWER✅✅the average speed of all the vehicles along a
given road segment at a typical instant in time
, Space Mean speed (equation) - CORRECT ANSWER✅✅Vs = Length of road segment/ average time to
traverse road segment.
For steady flows, the relationship between time mean speed and space mean speed - CORRECT
ANSWER✅✅Vt = Vs + σ^2/Vs
where σ^2 = variance of vehicular speed distribution in space, i.e. along the road segment of length L.
Time mean speed is always larger than space mean speed.
Concentration (definition) - CORRECT ANSWER✅✅(density) is the average number of vehicles present
at a typical instant on a road of unit length.
Concentration (equation) - CORRECT ANSWER✅✅K = average number of vehicles to traverse road
segment / length of road segment
Gap - CORRECT ANSWER✅✅Gap is the interval between the rear of a vehicle and the front of the
following vehicle
Gap units - CORRECT ANSWER✅✅m if measure in space
s if measured in time
Mean headway (definition) - CORRECT ANSWER✅✅ht, is the average time interval between successive
vehicles, measured from head to head, passing a given point.
Mean headway (equation) - CORRECT ANSWER✅✅pcu factor (category) = Headway (category) /
Headway (Passenger cars)
Mean spacing (mean distance headway) - CORRECT ANSWER✅✅hd, is the average distance between
successive vehicles, measured from head to head
Fundamental relationship of traffic flow - CORRECT ANSWER✅✅flow = concentration x space mean
speed
q = KVs
Flow (Volume) definition - CORRECT ANSWER✅✅Average number of vehicles passing a given point per
unit of time
Flow (volume) Equation - CORRECT ANSWER✅✅q = N/T
(N is number of vehicles)
(T is duration of time interval)
UNITS: Vehicles/hour (urban) Vehicles/day (rural)
Pcu - CORRECT ANSWER✅✅passenger car unit
What is Pcu used for - CORRECT ANSWER✅✅To calculate traffic flow across signalised junctions
Journey speed (definition) - CORRECT ANSWER✅✅(Overall travel speed) is the average speed of a
vehicle on a journey, including involuntary stops
Journey speed (equation) - CORRECT ANSWER✅✅Vj = distance travelled/ journey time
Running speed - CORRECT ANSWER✅✅Vr, as for journey speed but excluding stops
Spot speed - CORRECT ANSWER✅✅Vi , is the speed of an individual vehicle measured instantaneously
at a given point, e.g. by radar.
Time Mean speed (definition) - CORRECT ANSWER✅✅The average spot speed of all the vehicles passing
a given point during a period of time.
Space Mean Speed (Definition) - CORRECT ANSWER✅✅the average speed of all the vehicles along a
given road segment at a typical instant in time
, Space Mean speed (equation) - CORRECT ANSWER✅✅Vs = Length of road segment/ average time to
traverse road segment.
For steady flows, the relationship between time mean speed and space mean speed - CORRECT
ANSWER✅✅Vt = Vs + σ^2/Vs
where σ^2 = variance of vehicular speed distribution in space, i.e. along the road segment of length L.
Time mean speed is always larger than space mean speed.
Concentration (definition) - CORRECT ANSWER✅✅(density) is the average number of vehicles present
at a typical instant on a road of unit length.
Concentration (equation) - CORRECT ANSWER✅✅K = average number of vehicles to traverse road
segment / length of road segment
Gap - CORRECT ANSWER✅✅Gap is the interval between the rear of a vehicle and the front of the
following vehicle
Gap units - CORRECT ANSWER✅✅m if measure in space
s if measured in time
Mean headway (definition) - CORRECT ANSWER✅✅ht, is the average time interval between successive
vehicles, measured from head to head, passing a given point.
Mean headway (equation) - CORRECT ANSWER✅✅pcu factor (category) = Headway (category) /
Headway (Passenger cars)
Mean spacing (mean distance headway) - CORRECT ANSWER✅✅hd, is the average distance between
successive vehicles, measured from head to head
Fundamental relationship of traffic flow - CORRECT ANSWER✅✅flow = concentration x space mean
speed
q = KVs
