Travel study challenges TTI, measures trip lengths

Houston ranks 12th longest

Jon Boyd, Sep 30, 10.

Americans are spending more time traveling during peak hours because of the lengthy distances of their commutes, according to a report released yesterday by CEOs for Cities. The report called, “Driven Apart: How Sprawl Is Lengthening Our Commutes and Why Misleading Mobility Measures Are Making Things Worse,” measures total commuting time, while the old standard, The Travel Time Index in Texas Transportation Institute’s Urban Mobility Report (UMR) measures the ratio between free flowing traffic and congestion.

Houston is ranked 12th in terms of the longest travel times with an average of 226 hours of peak travel per year. The UMR ranks Houston 4th with a TTI of 1.33.

The Driven Apart methodology ranks Nashville, Oklahoma City, Birmingham, Richmond, and Raleigh as the regions with the five longest travel times, but UMR ranks them as 31st, 38th, 34th, 44th, and 33rd in terms of congestion, demonstrating a consequence of these differing methodologies. Similarly, there are great differences in the way the two reports rank the Chicago, Portland, and Sacramento regions, says the CEOs for Cities web site:

Driven Apart ranks how long residents in the nation’s largest 51 metropolitan areas spend in peak hour traffic, and in some cases the rankings are almost the opposite of those listed in the 2009 Urban Mobility Report.

For instance, the UMR depicts Chicago as having some of the worst travel delays, when it actually has the shortest time spent in peak hour traffic of any major US metro area. In contrast, Nashville jumped from 31st to first on the list of those with the longest peak travel times.

While peak hour travel times average 200 hours a year in large metropolitan areas, Driven Apart proves that some cities have managed to achieve shorter travel times and actually reduce the peak hour travel times. The key is that some metropolitan areas such as Chicago, Portland and Sacramento have land use patterns and transportation systems that enable their residents to take shorter trips and minimize the burden of peak hour travel. If every one of the top 50 metros followed suit with Chicago and other higher performing cities, their residents would drive about 40 billion fewer miles per year and use two billion fewer gallons of fuel, for a cost savings of $31 billion annually.

“It is more critical than ever that the US’s transportation investments be guided by accurate data – especially during these difficult financial times,” said Rockefeller Foundation Associate Director Benjamin de la Peña. “Transportation costs are often the second highest expense for working Americans, and we must make sure we are providing more transportation options to help them stretch their budgets. The Rockefeller Foundation is proud to support Driven Apart as part of our initiative to promote more equitable and sustainable transportation.”

The Texas Transportation Institute’s Urban Mobility Report is based on its Traffic Time Index, which is equivalent to the amount of time in congested travel divided by the amount of time in free-flowing traffic, according to the Driven Apart Executive Summary. “The Travel Time Index makes no allowance for the effects of longer travel distances on travel times,” says the Executive Summary.

The pie chart above illustrates the comparative analysis of travel in the Chicago and Charlotte regions. Chicago has a much shorter travel time: 48 minutes compared to 32.6 minutes in Charlotte. With over 38 minutes of un-congested travel time, Charlotte has a clear advantage over Chicago, with under 23 minutes of un-congested travel time. This also accounts for their TTI scores: Charlotte 1.25 and Chicago 1.43. Yet the TTI scores belie the fact that the travel time of Charlotte is fully 50% higher than Chicago’s

“Driven Apart” challenges the UMR methodology, and advances metrics based more on accessibility than mobility, writes Robert Puentes in the New Republic:

The critique, by Joe Cortright, argues that comparing travel times during rush hour to other times of day misses a key element: the lengths of those trips. Compare Charlotte and Chicago. While the TTI regularly identifies Chicago as one of the worst performers, Cortright’s study shows that not only are traffic delays in these two metros nearly the same, the situation in Charlotte is actually much worse since Charlotte travelers spend much more time on their trip and are exposed to traffic for a much longer period of time. The rub, according to Cortright, is that by failing to account for travel distance, it misses a key component of metropolitan traffic: land use and development patterns.

In fact, Cortright turns the whole thing on its head. Places like Nashville, Oklahoma City, Birmingham, and Kansas City that rank ok by the TTI are actually the worst performers according to the CEOs for Cities study. Conversely, Miami, New York, Sacramento, and Chicago turn out to be not so bad after all. In other words, the emphasis here is on accessibility (more economic and social interaction) rather than mobility (more movement).

“Driven Apart” claims that changing land use can be an effective means of reducing travel times and spending less on highways, reports the print version of ABC News (h/t Houston Tomorrow reader and architect, Joe Webb):

The conclusion of the report, called “Driven Apart,” is that the key to reducing rush hour traffic is to shorten the distance traveled. The report cites Portland - a biker’s Mecca - which has used smart land-use planning and has invested in alternative transportation, including a light rail line, to reduce average commuting times by 20 percent.

“‘Driven Apart’ adds to the growing body of evidence that shows compact development that puts many destinations close at hand has unexpected benefits - in this case, less time spent in traffic requiring less spending on highways,” Coletta said. “If we heed its findings, we’ll save time and money.”

[snip]

Tim Lomax, who oversees the Texas Transportation Institute’s traffic report, told ABC News he wasn’t sure why they were singling out his data.

“If we’re being blamed for the problem of sprawl and the choices of where people choose to live and work, I think [that that’s] great overstatement of our power,” Lomax said.
Lomax said his report isn’t perfect and that he’s always up for a discussion about the methodology, but that his goal has been to produce data and let people draw conclusions from it.

Driven Apart Press Release (pdf)
Driven Apart Executive Summary (pdf)
Driven Apart Technical Report (pdf)
Cities With the Worst Traffic Nightmares (Thanks to a tip from Joe Webb)
Everything You Know About Traffic May be Wrong
Report Cites Sprawl as Major Contributor to Travel Time

(Image credit: CEO’s for Cities)