March 16, 2009
Series Editor: Ian Parry
Managing Editor: Felicia Day
Assistant Editors: John Anderson and Adrienne Foerster
Welcome to the RFF Weekly Policy Commentary, which is meant to provide an easy way to learn about important policy issues related to environmental, natural resource, energy, urban, and public health problems.
Policymakers are increasingly interested in the idea of charging heavy-duty trucks by the mile for road use. In this week's commentary Robin Lindsey, one of the leading economists on transportation policy, examines the pros and cons of these types of tolls and whether trucks should have their own freeway lanes.
Has the Time Come for Truck-Only Toll Lanes?
By Robin Lindsey
Traffic congestion imposes a direct cost on U.S. freight transporters of $7.8 billion per year, according to the Federal Highway Administration. Recurring bottlenecks accounted for about 40 percent of total delays; the rest can be attributed to random sources of congestion such as accidents and road work, which upsets delivery schedules and inflicts a higher cost per hour of delay than recurring congestion. Truck traffic is growing more quickly than light-vehicle traffic and trucking is expected to remain the dominant mode of freight transport. Is it time for dedicated truck-only lanes?
The potential advantages of truck facilities have not gone unnoticed. Proposals for truck-only lanes or truck tollways have appeared in California, Florida, Georgia, Texas and Virginia. In 2002, Texas developed a plan to build a 4,000-mile "Trans-Texas Corridor" comprising rail lines, utility right-of-ways, and highways with separate toll lanes for trucks and passenger vehicles. However, in the face of stiff opposition from environmentalists and private land owners, the project has been scaled back. Another proposed project, the I-70 corridor, would span Missouri, Illinois, Indiana and Ohio. Truck-only corridors connecting the United States and Canada, and truck-only road networks in Britain, Italy, and the Netherlands have also been studied.
Dedicated truck-only facilities have several potential benefits. By adding road capacity, new facilities will relieve congestion and make deliveries quicker and more predictable. And by drawing trucks off existing roads, light vehicles will benefit too. Segregating light and heavy vehicles on existing roads could facilitate traffic because they differ in size, acceleration and maneuverability and therefore get in each other's way. However, on multilane highways without barrier separation, there are tradeoffs between average speed, lane speed differentials, frequency of lane changes, and fuel consumption.
Similar considerations determine whether segregating cars and trucks would reduce accidents. Overall accident rates per vehicle mile travelled are lower for trucks than cars, because professional truckers tend to be better drivers, and the actions of truckers are easier to predict than those of "4-wheelers". However, the risk of a fatality is greater in multi-vehicle accidents involving trucks, and these fatality risks are primarily borne by light-vehicle occupants. Surveys indicate that car drivers would be willing to pay to avoid sharing the road with trucks.
Truck-only toll facilities also generate revenue, which is becoming a priority for building new capacity and rehabilitating existing roads as the Federal Highway Trust Fund goes into deficit. A final and potentially significant advantage from building dedicated truck facilities is that it could reduce long-run infrastructure costs. Trucks require higher road-design standards than do light vehicles. By restricting trucks to part of the road network the remainder could be built to a lower standard. (For example, lanes could be restriped from 12 feet to 10 or 11 feet, increasing capacity if additional lanes can be squeezed in on urban expressways.)
Obviously, truck-only facilities also have disadvantages. Building new infrastructure is expensive and continuous rights-of-way may be unavailable. It is impractical-if not impossible-to segregate cars and trucks on all roads leading to and from dedicated truck facilities. Perhaps most important, because capacity is imperfectly divisible it is not generally possible to allocate it between light and heavy vehicles in ideal proportions. Even a single dedicated truck lane is not cost-effective if trucks comprise a small fraction of traffic.
Access restrictions and tolls
Truck-only toll facilities embody access restrictions and tolls. To understand their respective roles it is useful to consider a simple road network. The corridor in which truck-only facilities can be established comprises two parts, "road 1" and "road 2", each consisting of either a separate right-of-way or one or more traffic lanes (possibly barrier separated) of the same highway. Road 1 has a greater capacity than road 2. There are also untolled alternative routes that may not be designed to handle heavy vehicles.
Access restrictions and tolls can be used to pursue three goals:
- To distribute light and heavy vehicles (henceforth lights and heavies) that use the corridor efficiently between road 1 and road 2,
- To distribute lights and heavies between the corridor and alternative routes, and
- To generate revenue.
These goals may be at odds; for example, imposing high tolls on the corridor to generate lots of revenue may increase congestion on alternative routes. Even in this simple setting there are many options. Lights and heavies can each be allowed to use both roads or be restricted to one. And tolls may or may not be levied on each vehicle type on each road. Access restrictions alone generally do not meet any of the three goals because they do not generate revenue and they are an imperfect instrument for allocating traffic between the corridor and alternative routes. They allocate traffic efficiently within the corridor only if it is optimal to segregate lights and heavies onto separate roads. Heavies can be allocated to either road 1 or road 2, but in either case road capacities are unlikely to be ideally proportioned to handle the equilibrium volumes of lights and heavies.
Tolls, on the other hand, do generate revenue although it may fall short of paying the full capital cost of new infrastructure. Tolls are also more effective than access restrictions because they offer a continuous, rather than discrete, degree of control. But they do have limitations. Tolls cannot influence all margins of driver behavior such as weaving between lanes and driving speed. And shippers may impose constraints on delivery times that prevent truckers from shifting to off-peak hours in response to peak-period tolls.
Light and heavy vehicles differ in characteristics such as size, weight, safety, and emissions, and so to price road use efficiently, tolls have to be differentiated by vehicle type and route. Today, tolls can be differentiated by number of axles. Technological advances may soon permit tolls to be set in real time according to vehicle or axle weight, emissions, and other characteristics of the vehicle or driver.
Assessing the merits of truck-only toll facilities is challenging. For new facilities there are many design considerations: location, length, numbers of lanes and lane width, pavement thickness, entrances and exits, speed limits, services such as truck stops and refueling stations, and so on. Owner-operators and private carriers differ in the values they place on travel time and reliability and have shown different propensities to use toll roads. Toll road volumes have often been overestimated, sometimes by wide margins. Much of the trucking industry remains skeptical of road pricing as a way to relieve congestion and finance transportation infrastructure.
Nevertheless, the long-term outlook for truck-only-toll facilities appears promising. Transportation planners are grappling with growing funding shortfalls for highway spending caused by improving vehicle fuel economy and the erosion of real fuel tax rates due to inflation. Truck-only toll lanes offer a new revenue source, while also complementing the increasing interest in charging motorists by the mile through GPS or other electronic metering, to better address the broader social costs of transportation from congestion, pollution, and accidents.
Views expressed are those of the author. RFF does not take institutional positions on legislative or policy questions.
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