Increased congestion and proposed solutions

Published July 1, 2001

Contrary to well-publicized claims by the anti-automobile Surface Transportation Policy Project, cities that have emphasized transit over highways experienced the greatest increases in congestion over the past two decades. Cities that concentrated on highways instead of transit did fairly well at minimizing the burden of congestion on their residents.

Texas mobility report

The Texas Transportation Institute issued its annual mobility report on May 7, showing that congestion in most U.S. urban areas was worse in 1999 than the year before. The Institute’s carefully worded publication does not take sides on the vexatious question of what to do about congestion.

But the study does quantify many of the problems related to congestion. In the 68 urban areas in the study, researchers estimated congestion cost $78 billion and wasted 6.8 billion gallons of fuel and 4.5 billion hours of people’s time in 1999. Those numbers make for exciting newspaper headlines, but they have to be taken with a grain of salt, as they are based on several assumptions about road capacities and designs.

For example, the Institute estimates congestion cost people in the San Francisco Bay Area (including the San Francisco-Oakland and San Jose urban areas) 227 million hours and $3.9 billion in 1998, which works out to about 750,000 hours and $13 million per working day. By comparison, the California Department of Transportation estimates congestion cost about 112,000 vehicle hours (which works out to about 150,000 person hours) and $1.25 million per day.

This is not to say that one number is right and the other wrong. Both are in fact fairly crude estimates. The important point is that we have to be careful using these numbers. In fact, Texas Transportation Institute data are most reliable when comparing the changes in congestion over time, and less reliable when comparing congestion among urban areas for any single year.

For example, the report consistently rates Los Angeles as the nation’s most congested urban area, while New York is somewhere around number 13. Yet, relative to Los Angeles highways, most New York highways tend to have narrower lanes, shorter merge lanes at on- and off-ramps, and tighter curves, all of which reduce the flow capacities of New York freeways. Since the Institute doesn’t take these variations into account, New York congestion may actually be worse than congestion in Los Angeles.

The STPP response

This weakness in the data is not recognized by the Surface Transportation Policy Project (STPP), an anti-auto, pro-transit group that issued a report on the same day as the Texas study claiming “commuters suffer most” in urban areas “with the fewest transportation choices.” “Transportation choice” is a euphemism, of course, for spending transportation dollars on transit, especially rail transit, instead of highways.

STPP used the TTI data to compare congestion in various urban areas in 1999—exactly the kind of comparison the Texas data are least suited for. STPP also added its own factors in a convoluted attempt to measure “congestion burden” rather than just the cost of congestion. STPP’s congestion burden index is the Texas institute’s 1999 travel rate index times the percentage of commuters who drove to work in 1990.

Never mind that this is mixing 1990 and 1999 data. And even if that were not a problem, STPP’s index produces some very specious results. For example, according to the Texas Transportation Institute’s data, the average Bostonian spends twice as many hours stuck in traffic each day as the average Las Vegan. Yet because Boston has more transportation choices than Las Vegas, STPP ranks Boston one of the least congestion-burdened urban areas and Las Vegas as the second-worst congestion-burdened metro area in the nation.

Just why is sitting in traffic less of a burden because there is a rail transit system that doesn’t go where you need to go? STPP’s index may confuse cause and effect. High congestion may force some people to ride transit, but that doesn’t mean they are less burdened, especially since transit trips are generally slower than auto trips even in congested conditions.

A valid use of TTI data

If inter-metro area comparisons of Texas institute data are not valid (and made even less valid by STPP’s politically contrived manipulations), are the Texas data worthless?

No, the data are particularly valuable where they provide a time series from 1982 through 1999. These time series show what most urban residents know: that congestion is getting worse in almost every urban area of the country. Moreover, the data are valid for making inter-urban area comparisons of the changes in congestion over that time period.

For example, it may not say much to say that Los Angeles is ranked number one and New York number 13 in 1999 congestion because this ranking fails to account for the superior capacities of Los Angeles freeways. But it is more meaningful if the data show that New York congestion increased 50 percent faster from 1982 to 1999 than Los Angeles congestion. This suggests that whatever Los Angeles is doing may be working better at solving congestion than what New York is doing.

The Texas study uses several different measures of congestion, including:

  • The Travel Rate Index, which is the amount of additional time required to travel at peak periods due to heavy traffic. A Travel Rate Index of 1.2 means that a 10-minute trip at mid-day would take 12 minutes during rush hour.
  • The Travel Time Index, which is the amount of additional time required to travel at peak periods due to heavy traffic and roadway incidents. Since roadway incidents are both more common and more of an impediment during rush hour, this index is more realistic.
  • The Roadway Congestion Index, which is a direct comparison of miles traveled with the miles of road available to travel on.
  • Cost, hours of delay, and fuel wasted per capita, which measures the institute’s estimates of these costs per person.

There is a strong correlation (r-squared) between most of these indices. For example, there is a 98 percent correlation between the Travel Rate and Travel Time indices, and a 93 percent correlation between the Travel Rate Index and hours of delay per capita. (There is less than a 60 percent correlation between any of these measures and STPP’s congestion burden index.)

Changes in congestion over time

Looking at the changes in the Travel Time Index from 1982 to 1999, it turns out that New York congestion did increase 50 percent faster than Los Angeles congestion. Hours of delay per capita in New York increased 2.5 times more than in Los Angeles. Thus, having all those rail lines in New York doesn’t seem to have eased the burden of congestion all that much.

The table below shows the percentage change in the Travel Time Index, Travel Rate Index, Roadway Congestion Index, and hours of delay per capita (1999 hours minus 1982 hours) for each of the urban areas in the Texas study.

The delay per capita is shown as a difference rather than a percentage because percentage changes can be misleading. An urban area that moved from nearly no congestion in 1982 to some congestion in 1999 can have a huge percentage increase in the hours of delay per capita even though the 1999 hours of delay remain relatively small.

Many factors caused congestion to increase in some regions faster than in others, including population growth, urban layout, and the location and distribution of employment centers. But the one important factor under the control of transportation planners is how transportation funds are spent.

Over the past decade or so, the leaders of many urban areas, including Portland, the Twin Cities, and San Diego, have openly given up on highways to relieve congestion and funneled transportation dollars into transit instead. Other regions, such as Houston, Phoenix, and Kansas City, decided to stick with highways.

Results: Transit emphasis equals more congestion

Table 1 shows a clear result. Urban areas that focused on transit had the greatest increases in congestion.

My own home town of Portland suffered the greatest increase in the Travel Time Index, the second-greatest increase in the Travel Rate Index (scoring a fraction of a percent less than San Diego), and large increases by the other measures as well.

All of the top seven urban areas (as ranked by change in Travel Time Index) became fixated on rail rather than roads sometime in the 1980s or 1990s. Number eight on the list, Las Vegas, has been growing at nearly 6 percent per year—far faster than any other urban area—which is far faster than road agencies can build roads even if they have the political support.

Meanwhile, urban areas that focused on highways had relatively low increases in congestion. Thanks to aggressive construction of toll roads, Houston has barely recorded an increase in congestion. Phoenix and Kansas City also did well.

Thus, STPP’s claim that huge investments in transit ease the burden of congestion is almost certainly disproven by the Texas Transportation Institute’s data. In fact, the leaders of most urban areas that have elected to focus on transit see congestion as a tool to get people to ride transit.

As noted in The Vanishing Automobile (page 112), Portland planners say any relief from stop-and-go traffic (level of service F) “would eliminate transit ridership.” A 1996 transportation plan for the Twin Cities places a moratorium on new roads in the hope that, “as traffic congestion builds, alternative travel modes will become more attractive” (The Vanishing Automobile, page 465).

Thus, well-publicized efforts to increase “transportation choices” are almost certain to be accompanied by less-publicized decisions to increase highway congestion to force people to ride transit. This is exactly the opposite of the impression STPP tries to convey.

The real congestion solution: Value pricing

Historically, congestion has increased because the states elected to pay for roads using highway user fees based mainly on a cents-per-gallon tax. The inflation of the 1970s drove up highway costs without concurrently increasing highway revenues, while the fuel-efficient cars of the 1980s drove down revenues per mile driven. This left highway builders financially unable to keep up with the growth in driving.

As cars become even more fuel efficient, the long-term solution will be toll authorities, such as the one serving Houston, along with rush-hour premiums (value pricing) on those tolls.

Before that financial solution can be adopted, however, we must overcome the political problem, which is that the anti-auto lobby has convinced many political leaders that transit, not roads, is the solution to congestion. Those who want a real solution to congestion must prove that this is not true before they can press for toll roads and value pricing.

Transit and urban growth

As a side note, a recent Brookings Institution review of census data concludes that transportation policy is an important factor in urban growth. “Cities built for cars grew” between 1990 and 2000, say Brookings/Harvard analysts Edward Glaeser and Jesse Shapiro, “but cities designed for mass transit and pedestrians tended to shrink.”

Their report, City Growth and the 2000 Census: Which Places Grew, and Why, notes that “Cities with less than 65 percent of their commuters driving alone grew by less than 2 percent on average, while other cities grew by an average of more than 12 percent.”

Those who oppose automobiles might applaud this result, since many of them also oppose growth. But those who believe that growth is an important part of their regional economies should pause before endorsing transit-intensive and road-starved transportation plans.

Randal O’Toole is senior economist with the Thoreau Institute. He can be reached by email at [email protected]. Or visit the group’s Web site at