The Long and Winding Road in the Hawaii Guidelines

It’s called Saddle Road and it’s located on the Big Island.

Just so you know, I am not usually prone to clichés or Beatles song titles in my writing, so I am offering this apology for my previous blog title.

Panos (please see the earlier blog for Panos’ role in all this) found a really interesting case study that showed how very elementary analyses using good travel forecasting principles can be quite beneficial to project-level forecasts.  You can sometimes avoid large and expensive computer models by just paying attention to the fundamentals.  In any event, a good understanding of fundamentals can help you identify issues with a forecast done by presumably sophisticated methods.

I encourage you to read the full case study and perhaps give it to your students or mentees.  Here is a shortened summary.

Panos was trying to do forensic analysis of previously completed traffic forecasts for HDOT.  I don’t think HDOT was thrilled about the idea of dredging up the past, but Panos is a man who is difficult to dissuade when he puts his mind to something.

Panos found a forecast for a cutoff of Saddle Road.  The cutoff is now known as the Daniel K. Inouye Highway.  Panos disagreed with the original forecast, which showed a fair amount of traffic remaining on Saddle Road, and he decided to do it again, this time following the Guidelines.  Eventually, the cutoff opened for traffic.

Panos and his team used Wardrop’s First Principle combined with time series.  They reasoned that there needed to be an equilibrium between the cutoff and the old segment of Saddle Road.  Old Saddle Road was quite curvy (or winding, as Paul McCartney might say) and had many low-speed sections.  Upon further inspection it was clear that there would need to be a massive amount of traffic on the relatively-straight cutoff, causing significant delays, to justify any non-local traffic on Saddle Road.

The time series analysis showed such massive amounts of traffic would not be forthcoming.

The split between local and non-local traffic is pertinent to many bypasses of rural communities, but for the Saddle Road cutoff, the local traffic was considered to be tiny.  However, local traffic is not ignorable for many similar situations, such as tourist sites.  To meet this concern, the Guidelines provide extensive discussion of how vehicle re-identification technologies may be used to determine the amount of local traffic that should never be assigned to a bypass.

You can take your own virtual trip on Saddle Road with Google Street View.

Alan Horowitz, Whitefish Bay, February 23, 2017