Monday, October 04, 2010

Looking at congestion a different way

A new report on urban traffic skewers methods used by the widely quoted Texas Transportation Institute. In traffic circles, this is huge. The TTI's Urban Mobility Report is frequently used by cities to justify huge expenditures for wider streets and intersections. But it is deeply flawed, says a new report, "Driven Apart," from the nonprofit group CEOs for Cities. It doesn't consider that in some cities you don't have to drive as far as in other cities. The more compact cities, where you don't have to spend as much time in traffic, actually can end up looking more congested, because of the TTI's formulas.
Follow the links above to read the report.

Also, Streetsblog New York City has a good, readable analysis of it here. It opens this way:

Imagine two drivers leaving downtown to head home. Each of them sits in traffic for the first ten miles of the commute but at that point, their paths diverge. The first one has reached home. The second has another twenty miles to drive, though luckily for her, the roads are clear and congestion doesn’t slow her down. Who’s got a better commute?
Shockingly, the standard method for measuring traffic congestion implies that the second driver has it better. The Texas Transportation Institute’s
Urban Mobility Report (UMR) only studies how congestion slows down drivers from hypothetical maximum speeds, completely ignoring how long it takes to actually get where you’re going. The result is an incessant call for more highway lanes from newspapers across the country.

"Driven Apart" shows how the key tool contained in the Urban Mobility Report – the Travel Time Index – penalizes cities with shorter travel distances and conceals the additional burden caused by longer trips in sprawling metropolitan areas. It also looks at the reliability and usefulness of the methodology used in the UMR and finds it doesn't accurately estimate travel speeds, exaggerates travel delays and overestimates the fuel consumption associated with urban travel.

The report essentially makes the point that longer commutes are the main cause of time in traffic, not congestion per se.

"In the best performing cities – those that have achieved the shortest peak hour travel distances – such as Chicago, Portland and Sacramento, the typical traveler spends 40 fewer hours per year in peak hour travel than the average American. In contrast, in the most sprawling metropolitan areas, such as Nashville, Indianapolis and Raleigh, the average resident spends as much as 240 hours per year in peak period travel because travel distances are so much greater. These data suggest that reducing average trip lengths is a key to reducing the burden of peak period travel. Over the past two decades, for example, Portland, Oregon, which has smart land use planning and has invested in alternative transportation, has seen its average trip lengths decline by 20 percent."

If you want to see the chart showing all the metro areas studied, see page 7 of this link.

On page 10 of that link is a section showing why the report's authors say the Texas Transportation Institute's Travel Time Index (the TTI's TTI?) is flawed. The index is the ratio of average peak hour travel times to average free flow travel times. Here's what it says, using Charlotte and Chicago as examples:

"Chicago has a TTI of 1.43 (the second highest overall, behind only Los Angeles), while Charlotte has a TTI of 1.25 (just about equal to the average for all large metropolitan areas). This would appear to indicate that urban travel conditions are far worse in Chicago. But the traffic delays in the two regions are almost identical (40 and 41 hours per year, or about 10 minutes per day). Chicago has average travel distances (for peak hour trips) of 13.5 miles, while Charlotte has average travel distances of 19 miles. Because they travel nearly 50 percent farther then their counterparts in Chicago, Charlotte travelers end up spending a lot more time in traffic, about 48 minutes per day, rather than 33 minutes per day."

But the TTI makes it look as if drivers in Chicago have it worse. But if you look at hours spent in traffic they have it much better. The gives a flawed view of reality, the report says.

In sum, says the report:
"The Urban Mobility Report’s key measure – the Travel Time Index – is a poor guide to policy, and its speed and fuel economy estimates are flawed. In the aggregate, the analysis appears to overstate the costs of traffic congestion three-fold and ignores the larger transportation costs associated with sprawl."

It points out, for example, "There are strong reasons to doubt the UMR claim that slower speeds associated with congestion wastes billions of gallons of fuel. The UMR estimates of fuel consumption are based on a 29-year-old study of low-speed driving using 1970s era General Motors cars, which is of questionable applicability to today’s vehicles and to highway speeds."


Photo caption: Raleigh-Cary traffic, from photographer Shawn Rocco, [Raleigh] News & Observer

11 comments:

Anonymous said...

Better fix that link quick, Mary.

Mary Newsom said...

All the links are working for me. Which one is giving you trouble?

HokieTT said...

Another vote for telecommuting, when possible. If we'd just get these old school gray hair managers and execs to understand that white collar work is about the amount and quality of the work produced, and not the number of hours your butt is at your desk chair, we could lose enough traffic in key areas to relieve congestion seriously, and the people who live in outlying areas (identified as the keys in the new thinking in this piece) wouldn't have that long commute at all. Heck, even the environmental impact would likely be significant. And bosses wouldn't need as much office space on a day to day bases. Telecommuting...it's a win-win-win-win-win.

Anonymous said...

I'm a little confused by the Chicago versus Charlotte data. How do they come up with an average commute in Charlotte of 19 miles? According to Mapquest, Weddington is about 16 miles from uptown via Providence Road and Waxhaw is 23 mile. Huntersville is about 14 miles; Davidson is 21 miles. Mint Hill is a little under 13 miles. Concord is about 20 miles. I know lots of people live in these outlying areas and beyond, but do the vast majority of commuters go to far outlying areas? What about all the people that live within the 485 loop, which I suspect is a greater number of commuters than lives outside the loop (I live close to 485 in the south and we are about 11 miles from uptown)?
I've also lived in Chicago and wonder about the average commute of 13.5 miles. In the 70's, when I lived there, the commute to the suburbs was tough and long, and I imagine those suburbs and roads are a lot more crowded now. The distance from downtown Chicago to the suburb of Libertyville is over 34 miles, Palatine 29 miles, Hoffman Estates 27 miles. These are all popular places to live and there are many more huge suburban towns like them and just as far out, if not farther.
Could you explain how you or they came up with average commuting distance? Thanks!

Anonymous said...

Anonymous at 7:55 again. Are the average travel distances for Charlotte and Chicago one way or round trip? 19 miles round trip for Charlotte would make sense to me; however I would still have a hard time believing the 13.5 miles round trip for Chicago. Of course, there are some variables. In the Chicago area there are lots of business centers outside the loop so many suburbanites might be traveling to places much closer to their homes. We're just beginning to get some of that in the Charlotte area (Ballantyne, University area, Tryon/Arrowood/485). Can you sort it all out for us, Mary?

Anonymous said...

Good post, 7:55. Lots of people live inside 485.

I also endorse telecommuting. Been doing it for over 2 years and while I miss seeing my colleagues, I have Skype and other tools that keep me connected.

Michael said...

Ditto on the telecommuting.

The only congestion problem I have is stepping over the dog to get to the kitchen for another cup of coffee.... :)

Anonymous said...

"Chicago has a TTI of 1.43 (the second highest overall, behind only Los Angeles), while Charlotte has a TTI of 1.25 (just about equal to the average for all large metropolitan areas). This would appear to indicate that urban travel conditions are far worse in Chicago. But the traffic delays in the two regions are almost identical (40 and 41 hours per year, or about 10 minutes per day). Chicago has average travel distances (for peak hour trips) of 13.5 miles, while Charlotte has average travel distances of 19 miles. Because they travel nearly 50 percent farther then their counterparts in Chicago, Charlotte travelers end up spending a lot more time in traffic, about 48 minutes per day, rather than 33 minutes per day."


It says traffic delays are 10 minutes per day in each city at the begining and then 33 and 48 minutes per day later. Which is correct?

Because if both cities spend an average of 10 minutes in traffic per day, and Charlotte drivers travel further, then it makes sense that Chicago is worse b/c you have the same congestion in less distance traveled.

Anonymous said...

Is it traffic delays vs. traffic? That is a bit confusing in the article. It seems as though the Texas study is focused on CONGESTION while this study is focused on DRIVE TIME. I would think CONGESTION is more important.

From the article -

"The report essentially makes the point that longer commutes are the main cause of time in traffic, not congestion per se."

WOW, who would have guessed that longer driving commutes would result in longer times in "traffic."

Essentially, the report says that longer commutes causue longer drive-times. That is common sense. The Texas report's goal is to identify CONGESTION. The Texas report puts all cities on a level playing field by specifically excluding factors such as distance traveled.

Anonymous said...

Mary, I know you've gone on to another blog posting but several of us have had questions about this study. Could you please explain in layman's terms how the report came up with the commuting distances for Charlotte versus Chicago? Do you agree with their findings? Thanks!

Anonymous said...

Consistently throughout history, Americans have gravitated towards a half-hour commute, be it walking in colonial times, streetcar in the industrial era, or driving now.

What happens in bigger cities like Chicago is that employment has followed population desiring a half-hour commute. And the more congested a city becomes, then the shorter the average commute in total distance to retain about a half-hour commute.

And the half-hour rule is even mode neutral. Those who prefer not to drive (choice commuters, not transit-dependents) will seek out their residence within a half-hour transit, walking or biking route of work. Just as those who prefer to drive will choose where to live and work so as to achieve about a half-hour commute.