Evaluating Alternative Operations Strategies to Improve Travel Time ...

SHRP 2 L11: Final Appendices
able to provide. For example, the government in Germany has a goal to ensure that 80% of all
journeys have adequate, standardized real-time traffic and traveler information services by 2010
(8, 17 and 18).
Signal Retiming/Optimization. Traffic-signal-timing optimization and coordination minimizes
vehicle stops, delay, and/or queues at individual and multiple signalized intersections by
implementing or modifying signal timing parameters (i.e., phase splits, cycle length and offset),
phasing sequences, and control strategies. Effective signal retiming can increase capacity and
reduce signal delay, leading to lower travel times, improved reliability and reduced driver
frustration. For optimal performance, traffic-signal-timing plans need to be updated at least every
three to five years, and possibly more frequently depending on growth and changes in traffic
patterns. The cost of retiming a signal is approximately $3,000. If 25% of the approximately
265,000 signals in the United States are retimed every year, the annual cost would be roughly $200
million. Lack of resources (staff and funding) is the most-often-cited constraint for updating signal
timing plans (6, 14).
For example, the Traffic Light Synchronization Program in 43 cities in Texas reduced delay by
24.6% and lowered travel time by 14%. In Burlington, Canada, signal retiming at 62 intersections
lowered travel time by 7% (9). The National Traffic Signal Operation Self Assessment program
sponsored by the National Transportation Operations Coalition (NTOC) in partnership with the
Federal Highway Administration is a national effort to bring awareness to the need for additional
investment in traffic signal operations. Since 2005, a National Traffic Signal Report Card has been
published every two years that summarizes the results of self-assessments conducted by cities
nationwide. The document evaluates how signal retiming/optimization are being conducted by the
survey participants and points out outstanding needs to improve traffic signal operations (19).
Traffic Signal Preemption at Highway-Railroad Grade Crossings (HRGC). The railroad
traffic control system is required to provide a minimum warning time of 20 seconds to the
signalized intersection control system and such time is not always adequate to safely clear stopped
vehicles from the HRGC area. From a traffic engineer’s perspective, the current traffic signal
preemption strategies are viewed as a reactive action to trains approaching a nearby HRGC as the
20 seconds is less than a typical cycle length of 90 to 120 seconds. Instead, if notifications of
expected train arrivals at an HRGC could be accurately provided up to a cycle length before the
train arrival at the HRGC to the signalized intersection control system, safer and more proactive
preemption strategies could be adopted to provide improved safety and highway traffic operations
in the HRGC area (11).
Research on the application of low-cost ITS technologies to coordinate and optimize traffic signal
timing with train arrivals at grade crossings has been supported by the Federal Railroad
Administration (FRA) for the past several years. Several publications and test beds have been
successfully implemented by universities and DOTs. Most recently, Positive Train Control (PTC)
systems have been identified as the leading edge to the future of railroad and highway operations.
Positive train control systems are defined as “integrated command, control, communications, and
information systems for controlling train movements with safety, security, precision, and
efficiency” (11) as focus. PTC systems will reduce delays at HRGC by providing advance notice
of train arrival and traffic signal preemption optimization. PTC systems are currently tested by the
major Class I railroads in the U.S.
Traffic Adaptive Signal Control/Advanced Signal Systems. Responsive traffic operation
systems select a prepared timing plan based on the observed/measured level of traffic in the
system. Adaptive traffic signal control involves advanced detection of traffic, downstream signal
ADDITIONAL DESCRIPTION AND QUANTITATIVE BENEFITS OF TRAVEL-TIME RELIABILITY STRATEGIES Page F-9