Civil Engineering Reference
In-Depth Information
would consist of increasing the cost of private vehicle use and improving access to
alternative modes to the private car. Actions that reduce roadway capacity would
involve reducing the number of roadway lanes used by private vehicles and dedi-
cating them for public transport vehicles.
14.4 Strategies That Address the Causes of Congestion
Chapters
4
c congestion into four categories: (1)
peaking of travel demand; (2) concentration of activities; (3) area-wide traf
7
, classi
ed the causes of traf
-
c
demand growth exceeding capacity growth over time; and (4) recurring and non-
recurring bottlenecks. Strategies that address each of these causes are brie
fl
y out-
lined below.
14.4.1 Cause: Recurring Peaking of Travel Demand
When travel demand exceeds available roadway capacity (usually at least twice a day
—
the morning peak demand and the evening peak demand) the duration of stop-and-
go congestion is
longer
than the period when the demand exceeds capacity.
Example
Consider a bridge with an average directional capacity of 4,000 vph; a peak hour
demand volume of 6,000 vph; and demand volumes below capacity before and after
the peak hour.
Figure
14.2
shows the volume-capacity comparison before during, and after the
morning peak hour (8
9 am).
-
Fig. 14.2 Peaking of traffic demand
—
weekday mornings
