Evaluating Alternative Operations Strategies to Improve Travel Time ...

SHRP 2 L11: Final Appendices
Alternative left-turn treatments at intersections refer to non-conventional intersections. This
includes intersections where left-turn movements are converted to other intersection movements in
order to reduce the left-turn signal phase. Continuous flow intersections shift the left-turn several
hundred feet downstream to eliminate the left-turn signal phase.
Interchange modifications include changes to the interchange type, ramp configurations, and
traffic control of the ramp terminals.
5.2 Access Management
Access Management (Driveway location, raised medians, channelization, frontage road). The
intent of access management is to provide access to adjacent properties while maintaining a safe
and efficient transportation system. Access Management is an effective means to improve urban
street capacity and performance. Access control includes: raised medians, two-way left-turn lanes,
driveway consolidation, and signal spacing (6, 14).
Driveway consolidation (reducing the number of driveways on a roadway) has shown to improve
the travel speed along a roadway. Research has shown that directional free-flow speed decreases
about 0.15 mph per access point, while the Florida Department of Transportation has determined
that poorly designed driveways can reduce arterial travel speed by up to 10 mph (14).
An issue that often arises when retrofitting roadways to limit access points is opposition from
business owners who depend on the access points that are being closed/restricted/relocated. Cost is
another implementation challenge, particularly if right of way needs to be purchased.
Raised medians are installed to reduce turning movements and manage access to land uses along a
corridor. A full barrier completely limits turning maneuvers (except right-turns) and the number of
interruptions to traffic flow. Alternatively, limited access barriers can provide opportunities for
drivers to make left-turn movements where safe and appropriate. Raised medians improve flow
and performance by redirecting mid-block left-turning movements to signalized intersections.
Another strategy is to channelize or separate right-turn movements to minimize impedances to
through movements.
5.3 Signal Timing/ITS
Poor signal timing accounts for 5–10% of all traffic delay (1)). Optimizing signal timing is the
single-most cost-effective measure for improving arterial capacity and performance. Signal timing
is as important as the number of lanes on a roadway in determining the capacity and performance
of an urban roadway.
Transportation Management Center (TMC). TMCs are centralized facilities that gather traffic
information through cameras, loop detectors, radars, etc. to manage traffic conditions. One of the
main goals of a TMC is to optimize network operations by taking into account the variation of
demand throughout the day. TMCs are common in large metropolitan areas such as New York,
Chicago and Los Angeles to help agencies better respond to traffic incidents and other sources of
congestion. Despite the versatility of a TMC, its high implementation cost is a barrier in smaller
urban areas. Feasibility studies identify the appropriate components to implement in the TMC
facility (e.g., small urban areas may not need the transit AVL component) and make it possible to
implement a TMC in smaller urban areas.
In Europe, many countries have implemented regional traffic management centers. These regional
TMCs are helping European roadway agencies improve travel time reliability along and across
their roadway network borders. As a result of cultural shifts within European transport agencies,
drivers are viewed as consumers where reliable travel is one of the important services agencies are
ADDITIONAL DESCRIPTION AND QUANTITATIVE BENEFITS OF TRAVEL-TIME RELIABILITY STRATEGIES Page F-8