Evaluating Alternative Operations Strategies to Improve Travel Time ...

SHRP 2 L11: Final Appendices
Time of Day
Table B.2 - Illustrative Option Calculation for an Urban Freeway
Average Annual
Speed (mph)
Log Average Annual
Speed
Std Dev Log
Speed
Option Value
(mph)
Option Value (minutes per
mile)
14:00 57.11 4.02 0.25 5.64 0.115
14:05 56.56 4.01 0.29 6.49 0.137
14:10 55.16 3.95 0.42 9.25 0.219
14:15 53.78 3.92 0.43 9.14 0.228
14:20 52.52 3.89 0.45 9.34 0.247
14:25 51.08 3.84 0.50 10.09 0.289
14:30 50.81 3.84 0.48 9.69 0.278
14:35 50.01 3.81 0.51 10.16 0.306
14:40 48.02 3.76 0.53 10.10 0.333
14:45 46.31 3.71 0.57 10.37 0.374
14:50 45.03 3.67 0.59 10.47 0.404
14:55 43.64 3.63 0.60 10.24 0.422
15:00 41.52 3.57 0.61 9.92 0.454
15:05 41.11 3.55 0.63 10.19 0.481
15:10 39.47 3.49 0.66 10.21 0.530
15:15 37.48 3.42 0.68 10.00 0.582
15:20 35.79 3.38 0.67 9.39 0.596
15:25 34.15 3.32 0.67 8.97 0.626
15:30 33.69 3.31 0.67 8.80 0.630
15:35 33.93 3.32 0.66 8.75 0.615
15:40 32.68 3.28 0.67 8.54 0.650
15:45 29.00 3.15 0.67 7.59 0.734
15:50 26.30 3.05 0.64 6.64 0.771
15:55 24.67 3.00 0.63 6.06 0.791
16:00 23.16 2.94 0.61 5.53 0.812
16:05 23.10 2.94 0.60 5.42 0.796
Source: Counter data at I-405/I-90, South Bound, 2007. The calculations apply a guarantee
equal to the average speed for each time of day.
As previously stated, the data in Table B.2 are illustrative. They are provided to show the option
values associated with varying speeds and log-variability on a facility. In this table, the average
speed, log average speed, and the standard deviation are calculated from observed speed data. The
option value (mph) is calculated from the average log speed and log standard deviation calculated
from the data and the other inputs to the options formulation previously described using Equation
1.
Using Equation 1, the option value will be expressed in the speed reduction that drivers would be
willing to accept to obtain their speed guarantee. The option value, expressed in mph can be
converted to minutes by subtracting the option value in speed from the speed guarantee and
determining the additional average travel time the road user is willing to accept in exchange for
travel-time reliability.
DETERMINING THE ECONOMIC BENEFITS OF IMPROVING TRAVEL-TIME RELIABILITY Page B-13