Evaluating Alternative Operations Strategies to Improve Travel Time ...

SHRP 2 L11: Final Report
example, there is no way to know if there is a large family reunion planned for the coming
weekend, if there will be a massive warehouse fire during the next afternoon rush hour, or if
someone will run out of gas on a road with no shoulders during the morning commute. As a
result, agencies have avoided setting any kind of performance standard, particularly a
quantitative one, which they know cannot be met.
The literature review and stakeholder interviews conducted for this project identified few
instances in which roadway agencies have adopted policy goals or standards for travel-time
reliability. Exceptions to this are a limited number of cases involving HOV lane or high
occupancy toll (HOT) lane performance and where state DOTs have adopted general guidelines
stating that urban freeways should operate at no slower than the speed of optimal vehicle
throughput.
Another reason for not selecting specific roadway performance goals by agencies interviewed for
this project is that they do not have the necessary data to establish a baseline. As a result, they
are reluctant to set goals without knowing whether they can possibly meet those goals.
Consequently, outside of managed lanes, performance goals acceptable to the general public are
often “stretch” goals—even though this is not directly obvious to much of the public (whereas,
“zero fatal accidents” is obviously a “stretch goal” to the public).
Instead of adopting stretch or specific performance goals, transportation agencies have begun
adopting the third strategy listed above. As data become available to define the current baseline
conditions, they set “goals” to improve on those conditions. In terms of travel-time reliability,
this means setting goals to decrease the current mean travel times, to reduce the frequency of
occurrence of extreme travel times (improve travel-time reliability), while also reducing the size
of the travel-time increases when significant disruptions occur, all while accommodating
increasing use of the roadway system.
Because travel times differ by time of day (peak versus off-peak) and location (large urban
versus small urban versus rural), “improvements” are examined within the context of the current
baseline conditions. Similarly, agency operations (e.g., the speed with which incidents are
cleared, or the number of center-line miles of roadway for which real-time traveler information is
available) are compared against baseline conditions. In addition, once baseline conditions are
well understood, more-definitive goals can be set for those measures that describe the
performance of agency actions.
Suggested Actions for Goals and Targets
By setting goals and performance targets that fit the context of the current situation, agencies can
report on the effectiveness of their programs (capacity increases, operational improvements,
incident response programs) for improving roadway performance without being held to a
performance standard that assumes a volume/capacity ratio that is not attainable. This has the
added benefit of keeping agencies from being unfairly singled out for “not meeting national
standards” or for “setting unrealistic goals.” Where publically acceptable, realistic performance
targets can be identified, they may be adopted. Good examples of these exist for managed lanes
(e.g., HOT lanes that need to operate in free flow conditions 95 percent of the time during peak
periods) where the public has accepted the volume control measures (pricing) and the operating
agencies have devoted the incident management resources necessary to allow the goals to be
met.
GOALS AND PERFORMANCE TARGETS Page 35