Evaluating Alternative Operations Strategies to Improve Travel Time ...

SHRP 2 L11: Final Appendices
Comment #7:
Reliance on normal/lognormal distribution – again this is fairly standard in option theory in order
for the pricing to be tractable. The appendix would benefit from greater demonstration that this
assumption is appropriate for the types of data likely to be used. In particular, formal tests (e.g., a
Kolmogorov-Smirnov test) could be employed to evaluate the assumption and identify the
sensitivity of the results to departures from this assumption.
Response #7:
The authors agree with and appreciate the comments of this reviewer. The only response we offer
concerns the reliance on assumption of log-normality in the simpler (recurring events) setting.
Although it is true that little formal testing of the log-normality of speed data goes on, it is a widely
appreciated feature in practice. Vehicle counting systems PeMS, TRAK, and others are installed in
thousands of locations on US highways. These systems produce large quantities of high-resolution
traffic volume and speed data, and the log-normality of the distribution of speed is accepted as
commonplace. This does not mean that testing for compliance with this assumption should not be
done, of course. Analysts can be instructed to use statistical testing methods to confirm the
distribution of their data.
Additional citations were added to the appendix to support the appropriateness of our method in the
transportation context. For example, SHRP2 L03 cites the following paper, which confirms the use
of lognormal distribution for speed in the context of travel time reliability.
Rakha, Hesham, El-Shawarby, Ihab, and Arafeh, Mazen, Trip Travel Time Reliability: Issues and
Solutions, Intelligent Transportation Systems Conference, 2006. ITSC 2006. IEEE.
DETERMINING THE ECONOMIC BENEFITS OF IMPROVING TRAVEL-TIME RELIABILITY Page B-37