Highway Engineering

q=flow
s=saturation flow
x=q/ls

The first term in Equation 5.35 relates to the delay resulting from a uniform rate
of vehicle arrival. The second term relates to the delay arising from the random
nature of vehicle arrivals. The third term is an empirically derived correction
factor, obtained from the simulation of the flow of vehicular traffic.
The above formula can be simplified as:

(5.36)

where

C=correction term, which can be taken as 10% of the sum of the first two

terms

Equation 5.35 can thus be written in approximate form as:

dcA (5.37)

q

=¥ +09. ÊË ˆ ̄

B

A

x

B

x

x

=

()-

()-

=

()-

1

21

21

2

2

l

l

dcA

q

=+-C

B

The Design of Highway Intersections 143

Example 5.7 – Calculation of average vehicle delay at the approach to a

signalised junction

An approach has an effective green time of 65 seconds and an optimum cycle

time of 100 seconds. The actual flow on the approach is 1000 vehicles per

hour, with its saturation flow estimated at 1750 vehicles per hour.

Calculate the average delay per vehicle using both the precise and approx-

imate formulae.

Solution

c =100 s

l=0.65

q=1000 veh/h =0.278 veh/s

s =1750 veh/h =0.486 veh/s

x=0.278/(0.65 ¥0.486) =0.88

Contd