Evaluating Alternative Operations Strategies to Improve Travel Time ...

SHRP 2 L11: Final Appendices
5. Calculate the reliability measures and the benefit-cost ratio
6. Compare the results with other similar treatments
Step 1 – Characterize the Recurring Congestion Problem
A. Obtain speed data and calculate data parameters
B. Calculate the average speed and the standard deviation of the log of speed
C. Construct a log-normal distribution using the log mean and log standard
deviation of the speed to confirm that the speed data are log-normally
distributed
A. Obtain speed data and calculate data parameters.
The following parameters were calculated from the speed data. Refer to Exhibit 2 for the speed
data used in the calculations.
• 2001 95 th Percentile Speed = 23.65 mph
• 2002 95 th Percentile Speed = 27.91 mph
• 2001 Average Speed = 32.41 mph
• 2002 Average Speed = 36.39 mph
• Free Flow Speed = 60 mph
• Corridor Length = 4 miles
Table D.1 shows the eastbound State Road 520 freeway volumes for the three-hour weekday a.m.
peak period (from 6 a.m. to 9 a.m.) before and after implementation of the ramp metering.
Table D.1 - Vehicular Volumes
Vehicle Class 2001 Volume 2002 Volume
Passenger Car 6,516 6,921
Truck (3% of Total Volume) 202 214
Table D.2 shows the assumed value of time for each vehicle class. These values are based on
recommendations from the FHWA Highway Economic Requirements System
(http://www.fhwa.dot.ov/infrastructure/asstmgmt/hersdoc.cfm).
Table D.2 - Value of Time for Different Vehicle Classes
Vehicle Class
Value of Time ($/minute)
Passenger Car 0.30
Truck 0.83
SAMPLE PROBLEM-QUANTIFYING THE ECONOMIC BENEFIT OF IMPROVING TRAVEL-TIME RELIABILITY Page D-5