Civil Engineering Reference
In-Depth Information
coordination improvements, turn restrictions at key intersections, one-way streets,
reversible commuter lanes, movable median barriers during peak periods, better
lane striping, managing road access to and from traf
c generators, etc. They also
include the application of advanced technologies that use real-time information of
traf
c conditions to implement dynamic traf
c control strategies that optimize traf
c
fl
flow and provide travelers with real-time information on traf
c conditions.
16.3 Analysis Overview
Congested roadways and intersections generally can be identi
ed by observations
and from travel time and delay studies. Demand-to-capacity analyses are useful in
identifying problem locations. As a general guide, improvements should reduce the
demand-to-capacity ratio to less than 0.85 for achieving stable
flow. Reducing the
red times on each approach at signalized intersections can also reduce delays.
The 2010 Highway Capacity Manual [
1
] contains detailed procedures for esti-
mating capacity, delays, and facility performance. Additional guidelines are found
in the various editions of
fl
“
”
handbooks that are published by the
Institute of Transportation Engineers [
2
] and the Manual of Uniform Traf
Traf
c Engineering
c Control
Devices for Streets and Highways [
3
]. These procedures can be used to estimate
change in service levels resulting from traf
c operational improvements.
The sections that follow give descriptions, applications, guidelines, and travel
time savings for the following operational strategies:
Traf
c Signal Timing and Coordination
On-street Parking and Loading Zone Management
Intersection Turn Controls and Management
One-way Streets
Changeable Lane Assignment
Ramp Controls
Access Management
Intelligent Transportation Systems
Traveler Information Systems
Roadside Electronic Screening Programs for Commercial Vehicles
Integrated Corridor Management
16.4 Traffic Signal Timing and Coordination
Effective traf
c signal timing and coordination is one of the most basic and effective
strategies to reduce congestion. The Federal Highway Administration (FHWA)
indicates that there are more than 240,000 traf
c signals in the United States. The
agency estimates that poor traf
c signal timing accounts for 5
10 % of all traf
c
-
