Evaluating Alternative Operations Strategies to Improve Travel Time ...

SHRP 2 L11: Final Appendices
Figure D.2 – 2001 and 2002 Speed Data for Eastbound SR 520 from I-5 to east of Evergreen
Point Floating Bridge
The Solution
The travel-time variability during the a.m. peak period in the eastbound direction on State Road
520 generates a cost that is borne by users of the facility. This cost can be converted to a certaintyequivalent
value, which describes the additional time that motorists are willing to spend on the
facility if the variability in travel times is eliminated. This certainty-equivalent value of
unreliability can then be converted to a dollar value by applying the user’s value of time. The
resulting annual monetary value that results from improving travel-time reliability can be
compared with the cost of implementing the ramp meters to derive a benefit-cost ratio for the
treatment. The reliability improvement calculated in this Sample Problem was then compared with
improvements achieved at other locations where ramp meters have been installed.
Data Needs
• Speed data collected at five-minute (or fifteen-minute) time intervals
• Volume data by vehicle type
Cautions
• This procedure is applicable to data where the variation in travel-times can be characterized
by a log-normal distribution.
Procedure for quantifying the economic benefit of improving travel-time reliability
Six steps were followed to solve this problem:
1. Characterize the recurring congestion problem
2. Calculate the certainty-equivalent value of unreliability
3. Evaluate the treatment that reduces unreliability
4. Calculate the value of the reliability improvement to the road user
SAMPLE PROBLEM-QUANTIFYING THE ECONOMIC BENEFIT OF IMPROVING TRAVEL-TIME RELIABILITY Page D-4