Civil Engineering Reference
In-Depth Information
Fig. 14.1 Changes in
average traf
c speed and road
use (VMT) resulting from
strategies that change capacity
and/or demand
produces a reduction in VMT and a reduction in congestion. This is likely to exist
in areas where population and employment decrease.
3 Traffic demand remains the same (Do) and capacity is increased (S+)
:
Increasing capacity (S+) while traf
c demand remains the same (Do) reduces
congestion and increases VMT. This is likely to happen where the capacity increase
is implemented in a short time period (through operational improvements), while
population and employment remain constant. Most of the VMT increase on the
improved road results from traf
c diverted from other routes and or time periods.
4 Traffic demand remains the same (Do) and capacity decreases (S
−
): This
condition increases congestion and reduces VMT. Roadway capacity decreases in
high density areas, especially in the middle of the day, where street space is shared
with pedestrians, delivery vehicles, utility repairs, etc. In these cases congestion will
increase and VMT will decrease.
5 Capacity increases (S+) in response to increasing demand (D+): This
strategy aims at managing congestion to be within acceptable levels by balancing
expected demand growth with additional capacity. In this case VMT increases
while congestion is managed at acceptable levels. This condition is easiest to
implement in smaller metropolitan areas.
6 Traffic demand increases (D+) and roadway capacity decreases (S
−
): This
condition results in higher congestion and in VMT growth. It is typically found in
the megacities of developing economies where population and employment growth
increases land use density while transportation capacity growth does not keep pace
with growth in private vehicles use. Consequently the presence of too many people
and vehicles crowding the road space they share
reduces
the vehicle throughput
(capacity) of the road network.
7 Traffic demand decreases (D
−
) and roadway capacity increases (S+): This
condition is unlikely to be found in large metropolitan areas.
8 Traffic demand decreases (D
−
) and roadway capacity decreases (S
−
): This
condition would reduce VMT. Its impact on congestion would be determined by the
relative proportional decreases in demand and capacity. Actions that reduce demand
