The Congestion Problem
Over the past 20 years congestion has grown in every dimension – duration, extent, and intensity. The portion of the day impacted by traffic congestion has grown from 4.5 to 7.0 hours. Peak periods typically stretch from 2 or 3 hours in the morning and evening in metro areas above one million people. Larger areas can see 3 or 4 hours of peak congestion.
The extent of congestion has grown from 33 to 67 percent of travel. This statistic means that congestion affects more of the system. Many cities have a few places where any daylight hour might see stop-and-go-traffic. Weekend traffic delays have become a problem in recreational areas, near major shopping centers or sports arenas and on some constrained roadways.
The intensity of congestion as measured by the average delay penalty (the extra travel made each day due to congestion) has increased from 13 to 37 percent in the past 20 years. In other words, peak-period trips required 37 percent more travel time in 2003 than a free flow trip at midday, up from 28 percent 10 years earlier. Trips to work and school take longer, but so do shopping trips, doctor visits, and family outings.
The consequences of congested roadways in the U.S. are both monetary and societal. The cost of congestion for the 85 urban areas in the Texas Transportation Institute’s (TTI) 2005 Urban Mobility Report was estimated to be $63 billion based on the 3.7 billion hours of delay and 2.3 billion gallons of wasted fuel calculated in those areas. This congestion cost to the U.S. economy in 2003 was equivalent to 0.6 percent of the Gross Domestic Product (GDP). Moreover, these congestion costs are growing at 8 percent per year, more than double the growth rate of the economy, so that in 20 years congestion costs are expected to rise to 1.6 percent of GDP. But these published estimates likely account for less than half of the overall costs for transportation congestion. Additional costs include:
- Costs of congestion in rural areas and smaller cities outside of the 85-city TTI sample;
- Loss of productivity due to reduced scale economies and labor market sizes;
- Safety costs;
- Vehicle wear and tear on passenger cars;
- Costs of cargo delays;
- Inventory costs of bigger stocks required by congestion-related unreliability in shipment times; and
- Costs to passengers of having to leave early for a destination because of congestion-related unreliability in travel times.
Congestion is Costing Me How Much? In the top 85 (of 400) urban areas (i.e., those areas that account for the worst congestion indices) the average annual cost of congestion per traveler (including the cost of time and operating a vehicle) ranges from $222 (small urban areas) to $1,038 (large urban areas) and averages $794. (2005 Urban Mobility Study, |
Not only does congestion dampen the economy, it also impacts the way we live: Parents miss events with their children; friends and families find it harder to spend time together; and civic participation is increasingly difficult. Evidence suggests that each additional 10 minutes in commuting time cuts involvement in community affairs by 10 percent.
The root causes of congestion have long been understood, and there is now broad consensus that congestion generally reflects a fundamental imbalance of supply and demand. That is, during hours of peak usage of the transportation facilities most desirable to motorists, the supply of, for example, roadway capacity is insufficient to meet the demand for those facilities. Economists have long understood that such an imbalance stems from inefficient pricing, where the true costs of usage are not reflected in prices paid by the users. For example, travelers are not generally charged for the impact their trip will have on others using the same facility (e.g., increased levels of congestion) or on other members of society (e.g., increased air pollution). In fact, in this country, access to highway travel is, for the most part, rationed by delay.
The imbalance of supply and demand leading to congestion is also impacted by the absolute volume of traffic (e.g., demand) on a given facility relative to its physical capacity (e.g., supply). When we look at traffic congestion from a demand perspective, we are looking at how many vehicles compete for space on a particular facility at a given time. The demand for a facility is a function of individual decisions as to when, where, how, and even if highway travel will take place.
Washington Post, A June 2007 article in the Washington Post laments the difficulty parents in outlying suburbs have in attending their kids’ evening soccer, t-ball, baseball, and softball games. Parents who are coaches, and have responsibility to be early to set up the field, have an especially hard time, often arriving in their office clothes directly from work. Games are routinely pushed back 30 to 60 minutes; leagues are over taxed because only one, and not two, games can be played per evening on the same field. |
On the supply side, congestion is primarily a function of the physical characteristics of the facility and events that limit the availability of this capacity. Congestion driven by supply side considerations is characterized as either "recurring" or "nonrecurring." This distinction is useful in helping the community of transportation professionals devise strategies that will either mitigate or reduce congestion. Recurring congestion happens in roughly the same time and place on the same days of the week. It results when physical capacity is simply not adequate
to accommodate demand during peak-periods. On the other hand, nonrecurring congestion is caused by events such as work zones, traffic incidents, and bad weather. Obviously, when these nonrecurring events occur on an already con-gested facility the impacts are magnified. Figure 1 presents a pie chart showing the factors that cause on-the-road congestion.
Improvements Are Possible! "Seven of 18 bottlenecks identified in 1999 – including hot spots in Houston, Albuquerque, Denver, Boston, Los Angeles, and Washington, D.C. – no longer appeared on our ranking of the country's worst chokepoints (due to) major reconstruction projects completed or underway." |
Figure 1. Sources of On-the-Road Congestion
