Civil Engineering Reference
In-Depth Information
Reversible lanes on streets can be controlled in various ways:
Using both curb-mounted and overhead signs are used.
Overhead lane control signals that conform to the National Manual on Uniform
Traf
c Control Devices [
3
].
Traf
c cones and portable barriers.
Movable physical barriers are typically used on bridges and on freeways.
A common practice is to use physically separated roadways on freeways and to
control entry by electronically operate gates. Implementation of reversible
ow
lanes is applicable for freeways and arterial streets with automated lane control
technologies (sensors and lane control signs).
fl
16.9 Ramp Controls
Ramp meters and entrance controls are integral parts of many freeway management
programs. They control the rate at which ramp vehicles enter the freeway during
peak periods to
prevent
a speed reduction and a lower volume throughput of the
freeway lanes. Metering is most effective when the freeway operates at service
levels of
“
E
”
or
“
F
”
.
16.9.1 Applications
Ramp controls work best when the following conditions apply [
25
]:
recurring peak period traf
c congestion along the freeway (e.g., demand exceeds
capacity)
there are suitable alternative surface routes that can accommodate traf
c diverted
by the metering strategy (e.g., available continuous frontage road along the
freeway)
the travel time saved by the freeway traf
c exceeds the additional delay that
diverted traf
c imposes on surface routes
adequate ramp storage for vehicles waiting to enter the freeway (to avoid
spillback onto surface streets)
16.9.2 Control Types and Methods
There are several ways to apply entrance ramp controls. Methods include:
(a) permanent or part-time closure
(b) pre-timed or traf
c responsive ramp metering
