Vehicles enter the toll plaza. Tolls for the Chesapeake Bay Bridge went up in 2011. (Michael S. Williamson/WASHINGTON POST)

A new study by the Government Accountability Office finds that variable tolling can help reduce congestion on U.S. highways, while also focusing attention on the fairness of such transportation systems.

So far, there are few examples of variable tolling in the D.C. region. But that is changing, and other urban areas already have built up some experience with them. The GAO report to Congress, released in January, addresses many of the concerns raised by people who drive along or live near Maryland’s Intercounty Connector and the privately built Dulles Greenway, as well as those awaiting the opening of the high-occupancy toll lanes on the Capital Beltway in Virginia.

Tolling techniques

Variable tolling takes several forms. Each is a response to congestion, and to the fact that limited space and limited revenue reduce the likelihood that new lanes will be built without toll financing. The new forms of tolling are used not only to pay for construction and to reward investors, but also to manage traffic through a technique known as congestion pricing.

Congestion pricing in the United States comes in one or two forms, the GAO report said. High-occupancy toll (HOT) lanes vary the toll according to current demand. The varying toll moderates the number of drivers entering the lanes so speeds can stay at 45 to 55 mph. The 495 Express Lanes on the Beltway and the other HOT lanes planned for Interstate 95 will be examples of that. HOT lanes offer a free ride to those meeting the HOV requirements, but charge other drivers.

The other format bases the toll on time of day, charging a pre-set premium price for travel during peak periods. The Intercounty Connector and Dulles Greenway follow that model. The traffic management goal is similar: The changing toll encourages drivers to use the highway when it’s likely to be less congested.

History and future

The first congestion pricing project in the United States was launched in 1995 in Orange County, Calif. The GAO report now counts 41 pricing projects either open or under development on highways, bridges, and tunnels. Tolls range from 25 cents to $14.

It looks like the way of the future. Some regions are planning networks of HOT lanes, the report says. (Virginia would be one of them, but Dallas-Fort Worth, Atlanta, Minneapolis-St. Paul, Seattle, and the San Francisco Bay area also are among those planning for such networks. The Metropolitan Transportation Commission of the San Francisco Bay Area proposes having a 570-mile network of HOT lanes by 2025.)


So how are they doing? The report describes the results of its research and other studies that examined how variable tolls have performed in relation to five goals. But the researchers note that not all projects were evaluated and that there are limits on the assessments.

1) Did travel time and speed improve? They improved on at least some sections of the five HOT lane projects evaluated. Sometimes, the GAO said, the improved travel times in the HOT lanes also led to improved travel times in the adjacent general purpose lanes. For example, a study found that peak-hour speeds on the untolled lanes along SR 167 in Seattle had increased by as much as 19 percent in 2010 compared with travel speeds in 2007.

Evaluations of nine peak-period pricing projects showed no effects on travel time and speed, the GAO said.

2) Did the tolled lanes move more people and vehicles? While there were more cars using the HOT lanes, the GAO report said, there were on average fewer people in the cars. HOT lanes project sponsors attributed that to an increase of the share of toll-paying solo drivers or to a decrease in carpooling in the HOT lanes. Evaluations of peak-period pricing projects found no increase in the throughput of people and vehicles related to congestion pricing.

3) Did drivers change their behavior to travel at off-peak times? The sponsors of HOT lane projects on I-15 in San Diego and SR 91 in Orange County surveyed drivers to see whether they changed their trips times to off-peak. In the I-15 survey, some traffic shifted from the peak hour to times just before or after, but the study didn’t explain why the shift occurred. Drivers surveyed for the SR 91 evaluation said the level of congestion affected their timing decisions more than the toll.

Sponsors of peak-period tolling projects conducted more elaborate studies, which made sense, since encouraging off-peak travel was a prime goal of their tolling systems. Their studies showed some success in reducing congestion during peak times as drivers chose to travel off peak.

4) Did some drivers switch to transit? Results on the HOT lanes projects were mixed. The I-95 project in Miami was the only one with demonstrated increases in transit ridership, the GAO report found. Between 2008 and 2010, the average weekday ridership on the I-95 express bus increased by 57 percent. About 38 percent of these riders said they used to drive alone.

The other three HOT lanes evaluations found no increase in transit ridership on buses using the HOT lanes as a result of the projects, the GAO said. Evaluations of three peak-period tolling systems found no evidence of changes in transit ridership

5) Do variable tolls distribute impacts fairly? Three HOT lanes evaluations — for SR 91 in Orange County, I-394 in Minneapolis, and SR 167 in Seattle — considered the effects of congestion pricing on drivers with different incomes. The results indicated that drivers of all incomes used the HOT lanes, but high-income drivers used them more often. Evaluations for those projects plus I-15 in San Diego found that drivers liked having the option of using the HOT lanes and supported them.

Evaluations of nine peak-period tolling systems considered various fairness issues and found few impacts, the GAO said.

Do the tolling systems push drivers off the tolled roads in search of other routes and impose a burden on nearby neighborhoods? The sponsor of the SR 91 HOT lanes project in Orange County reported that traffic was drawn to the roadway, rather than pushed away, because the tolled lanes were new and added capacity.

Two sponsors of peak-period tolling systems studied traffic diversion, but found no evidence that motorists were shifting to adjacent roads.

Communities along the route of the Intercounty Connector are concerned about extra traffic on roads near interchanges. The connector was too new to be included in the GAO findings, but it’s a bit different. The connector is a completely new road, rather than one to which tolled lanes have been added.

The goal of the connector’s planners was to take some traffic off existing east-west routes and put it on the new highway. The variable toll would tend to reduce extra congestion around interchanges at peak periods.

Tolling does mean that those who benefit most directly from using new lanes will pick up a greater share of the expense. But the report urged continued scrutiny of that burden, particularly when tolling is used not only to manage congestion but also to meet revenue targets.