Evaluating Alternative Operations Strategies to Improve Travel Time ...

SHRP 2 L11: Final Report
near-real-time traveler information to the traveling public. In most cases, these data are also
stored so that they can be used for later analysis and performance reporting. Unfortunately, not
all data that is currently collected and used in real time or near-real time are stored and made
available for management and planning purposes. Older traffic management systems built in the
1980s and early 1990s often lack significant data storage and reporting capabilities. The data
collected by traffic-signal systems are a primary example. The majority of modern traffic signal
systems have some level of detection on the approaches to intersections. However, most traffic
signal systems routinely discard the data collected at signals. The data are simply not stored for
later use, and even signal systems with good data-collection capabilities often have limited
reporting capabilities.
Before the current generation of computer and communications technologies, it was prohibitively
expensive to transmit, store, and use these data to report signal and intersection performance.
While technology now makes these tasks much more cost effective, limited budgets and a lack of
incentive to conduct routine performance reporting on arterials has meant that the state-of-thepractice
has not changed appreciably, despite changes in costs and capabilities. This is an area in
which considerable improvement could occur if priorities allowed the allocation of resources to
address the problem.
Disruption Data
A second category of data required for performance reporting describes disruptions that cause
non-recurring travel delays. Without these data, it is impossible to determine whether changes in
roadway performance are due to the actions of the operating agencies or because of changes
outside of the control of those agencies. The data are needed for the following reasons:
• To improve roadway agencies’ operational decision making in real time;
• To support traveler information services;
• To determine the causes of unreliable travel in “planning time”; and
• To evaluate the effectiveness of programs implemented to improve travel-time reliability.
The availability of data on travel disruptions is similar to that of data on travel times. As a result,
data are more commonly available on freeways in congested urban areas with significant
operational improvement programs than they are for rural areas, smaller urban areas, and
arterials.
Traffic Incidents
Accident data are routinely archived in state databases. Whether these data are available in nearreal
time is a function of whether real-time traveler information and/or active traffic-management
activities are ongoing in the geographic region where an accident takes place.
In major urban areas, the private sector often does an excellent job of tracking accidents. These
reports are used in private sector–funded traveler information services. However, the accuracy of
private sector databases is often not up to the standards desired by some roadway agencies. What
may or may not be available along with the accident data (regardless of their public or private
source) are statistics on the nature (e.g., size, severity, duration) of the accident, its disruption of
roadway operations (e.g., the number of lanes closed), or the response to it. These data tend to be
available only where specific incident-response programs have been implemented to collect
them. Similarly, data on traffic incidents (stalled or disabled vehicles, debris) are also available
only when such programs exist.
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