Capacity Evaluation Along Benin-Lagos Expressway by Traffic Flow and Time Headway Approach

Abstract

Highway capacity is defined as the maximum number of vehicles
which can be accommodated in a given roadway under prevailing
conditions. It is affected by desired speed, number of lanes, vertical
grade, composition of traffic etc. In this paper, the traffic flow and
time headway approach were employed to determine the capacity of
a section of the Benin - Lagos Expressway in Edo State, Nigeria. The
moving observer method was used to acquire the necessary data in
the mornings (i.e. between 7:00-9:00am) and at evenings (i.e.
between 4:00-6:00pm). The Greenshield model was also employed
to show the relationship between the space mean speed and the
density. From the analysis carried out, it was observed that the
average space headway and average time headway were respectively
0.025km (25m) and 2.26sec, indicating a moderate traffic flow as it
relates to the time headway and space headway. This indicates a
relatively low probability of accident occurrence based on the mean
free speed. The model developed gave a mean free speed of
66.161km/hr, which is the allowable maximum driving speed when
flow and density are zero. The jam density obtained was 102 veh/km.
Capacities obtained due to flow and time headway are 1687veh/hr
and 1593veh/hr respectively.