A new study questions federal efforts to promote the use of toll roads throughout the country by documenting certain negative side effects tolls have on secondary road networks. Researchers Peter Swan of Penn State University and Michael Belzer of Wayne State University presented their findings Monday to the Transportation Research Board annual meeting in Washington, DC.

"If private operators -- or public operators for that matter -- set toll rates to maximize profit where congestion is not a significant problem, they can introduce substantial inefficiencies in the overall road transportation network and actually increase congestion and safety hazards in other parts of the system that they do not own and control," Swan and Belzer wrote. "These inefficiencies, the cost of which are borne by the public and not by the private toll road owner who is focused on profit for his particular part of the network, can only exist when private operators control particular strategically located roads through a purchase or long-term lease."

The researchers analyzed decades of data from the Ohio Turnpike and nearby alternate routes in Ohio, comparing both to national data to determine the effects the toll rates had on nearby free roads. Ohio raised toll rates in the 1990s and subsequently lowered them, allowing an easier calculation of the effect of different rate levels. The study showed that as the Turnpike toll increased, truck traffic increased on alternate, free routes as truckers balanced the monetary savings with the cost of the extra time needed to take an indirect route.

Swan and Belzer's economic modeling showed that the Turnpike could maximize its revenue by setting a truck toll rate of 46 cents per mile and collecting $111 from each truck driving the length of the Turnpike. At this high rate, however, the number of trucks avoiding the toll road would quadruple and place 608 million vehicle miles of added traffic and wear on secondary roads.

The study did not directly examine accident rates but the results suggested that imposing tolls on divided highways would increase the number of road fatalities by pushing truck traffic onto roads not designed to handle heavy truck traffic.

"Because we know that secondary roads pose greater safety hazards, the safety cost of diversion will be substantial," the study explained. "We know enough about the frequency and severity of crashes based on highway type to suggest that a substantial increase in crashes, crash severity, and fatalities in the state of Ohio probably would occur as a result of this diversion."

Swan and Belzer noted that efforts to "monetize" existing toll roads is a recipe for the level of higher toll rates that increase truck diversion. In Indiana, for example, toll rates rose 70 percent on the Indiana Toll Road just before its sale to a Spanish-Australian conglomerate -- the rate hike boosted the asset value to $3.85 billion. In the next three years, toll rates will rise another 78 percent.

"It is important that the effect of shifting from fuel taxes to tolls as well as highway privatization be understood better before the United States implements changes that will be very costly to reverse," the study concluded.

A full copy of the study is available in a 160k PDF file at the source link below.