Civil Engineering Reference
In-Depth Information
(c)
traf
c responsive merge control
(d)
integrated system controls that apply to a series of entry ramps along the
freeway
Metered freeway ramps that operate in a single lane should have a full width
shoulder to allow for emergency passing. A common practice is for buses and car
pools to bypass the ramp controls. In these cases an additional full-width bypass
lane should be provided [
2
,
26
].
16.9.3 Benets
Typical bene
ts reported from freeway ramp metering include [
23
]:
in the Minneapolis-St. Paul region system-wide ramp metering has increased
freeway throughput volume by 30 % and peak period speeds by 60 %, with
travel time decreases of 14
-
27 %
ramp metering along freeway corridors in other cities have found that freeway
travel times decreased by 7 % (Portland, Detroit), 27 % (Denver), 38 %
(Austin), and 48 % (Seattle).
ramp metering, however, creates queues at entry ramps, that can cause trafcto
divert to local streets, resulting in increased delay on local streets.
in Minneapolis-St. Paul, however, when the ramp delays were included, the total
delay was still substantially reduced.
16.10 Access Management
Access management is a proactive strategy that balances the need to minimize
traf
c delay and crashes along arterial roadways with the need to provide access to
land development activities adjacent to the roadway. It applies to both existing and
new roadways. It extends the concept of access control to these roads by de
ning
access spacing standards, providing suitable geometry, and establishing the nec-
essary legislative authority to implement the desired standards.
The primary goals of access management are to improve safety and to maintain
desirable traf
c speed and capacity along arterial roads and streets. These goals are
achieved by coordinating and consolidating the number and location of curb cuts to
adjacent land development, and by controlling the spacing of traf
c signals along
arterial roads. As noted earlier, each traf
c signal per mile added to the roadway
reduces speed about 2
3 mph.
There is a large repertory of access management techniques [
7
] including:
separating and physically restricting left turns; restricting curb cuts and direct access
to driveways; establishing access spacing requirements; separating obvious con
-
fl
ict
