Evaluating Alternative Operations Strategies to Improve Travel Time ...

SHRP 2 L11: Final Appendices
C. The value of the reliability improvement for the three-hour a.m. peak period is calculated
as:
Total length of the highway = 4 miles
∴Total value of the reliability improvement for the three-hour a.m. peak period
= ($103.82 + $8.88) X 4 (miles) ≈ $450.80
D. The total annual value of the reliability improvement
The total number of days considered = 252 Weekdays/Year
∴Total value of the reliability improvement per year (for the three-hour a.m. peak period)
= $450.80 X 252 days ≈ $113,601.60
Step 5 – Calculate the Reliability Measures and the Benefit-Cost Ratio
A. Calculate before and after Buffer Index (BI) and Planning Time Index (PTI).
B. Calculate the benefit-cost ratio.
A. Calculate the reliability measures
The Buffer Index (BI) and the Planning Time Index (PTI) were calculated using the collected
speed data. By definition, the Buffer Index is estimated by computing the 95 th percentile travel
time minus the average travel time divided by the average travel time. The PTI is obtained by
the ratio of the 95 th percentile travel time to the Ideal or Free Flow Travel Time.
The required input data is listed below:
2001 95 th percentile travel time: 605.8 sec
2002 95 th percentile travel time: 513.4 sec
2001 average travel time: 442.1 sec
2002 average travel time: 393.8 sec
2001 free flow travel time: 238.8 sec
2002 free flow travel time: 238.8 sec
Table D.3 shows the computed PTI and BI values from the data collected during 2001 (before)
and 2002 (after).
Table D.3 - 2001 and 2002 Buffer Indices and Planning Time Indices
Reliability Measure Before
(2001)
After
(2002)
Planning Time Index 2.54 2.15
Buffer Index 0.37 0.30
The results show a clear reduction in both the PTI and the BI after the eastbound ramp meters
were implemented in late 2001 during the a.m. peak period to alleviate congestion.
B. Calculate the Benefit-Cost Ratio
This last step in estimating the monetary value of travel-time reliability consists of comparing
the Total Annual Value of Reliability Improvement (Step 4D) with the implementation cost for
SAMPLE PROBLEM-QUANTIFYING THE ECONOMIC BENEFIT OF IMPROVING TRAVEL-TIME RELIABILITY Page D-11