Road Management & Engineering Journal
Road Management & Engineering Journal
February, 2000
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Axles to Grind: Driving Questions About the Limits to Place on Trucks Traveling Our Roads

(This article is reproduced, with permission, from the November/December 1999 (Vol. 70, No. 6) issue of Washington Journey, published by AAA (American Automobile Association) Washington. Permission to reproduce was granted by Allison Joyce, Editor.)

By Tom Lankard and John Lehrer

Many of us have seen the bumper sticker that says, IF YOU BOUGHT IT, A TRUCK BROUGHT IT. Good point. After all, just how does that washing machine get to your local appliance store, that snazzy new car to your local dealer, or even salad makings to the fast-food joint down the street? Probably by truck.

When it comes to moving goods and cargo, trucks are a crucial element in the nation's economy; they account for almost 80 cents of every $1 spent to haul freight. There are several types of large trucks, from the single-unit truck, so-called because the cargo box and cab are wedded into one frame (a local moving company's truck, for example), to the familiar semi or "double," with a tractor pulling one or two trailers.

All these have limits on their size and weight. Congress began imposing such limits in 1956; federal law now restricts the length of tractor-semitrailer combinations to the tractor plus one 48-foot trailer or two 28-foot trailers and the total weight (including cargo) to 80,000 pounds. Limits on larger trucks were first imposed by Congress in 1991 and extended in 1998. Many states, however, have exemptions and "grandfather rights" that allow bigger, heavier trucks to continue to operate where they already were permitted.


The American Trucking Association wants bigger trucks allowed on our highways. "We support the use of longer combination vehicles at state option," says Ted Scott, director of highway policy for the ATA. At its annual meeting in June, the Western Governors Association considered a resolution to allow states to "harmonize" their truck size and weight limits. Though the governors tabled the resolution in favor of further study, if such a resolution were passed and presented to Congress, it could open the door to raising states' limits to the highest common denominator, a scenario AAA opposes.

Longer combination vehicles, or LCVs, are three extraordinary trailer configurations that 21 states currently allow in one form or another. The shortest of these is the Rocky Mountain double: a cab followed by a 48-foot trailer and a 28-foot trailer--about 95 feet overall, almost one-third the length of a football field. The next-largest is a triple-trailer combination: a cab plus three 28-foot trailers, about 105 feet long. The turnpike double, a behemoth consisting of two 48-foot trailers plus the tractor, measures about 110 feet--almost eight times the length of the average car and as long as a Boeing 737-700. The heaviest LCV can tip the scales at more than 140,000 pounds, or more than 40 times the weight of the average car.

Trucking industry strategy has been to increase limits state by state; when size and weight limits are increased in one state, adjacent states feel pressured to conform to stay economically competitive. Rocky Mountain and turnpike doubles are currently allowed in Oregon and Idaho. The largest truck Washington permits on its roadways is a smaller version of the Rocky Mountain double, with a total trailer length of up to 68 feet and a maximum weight of 105,500 pounds.

Illustrations by Tim Barker -- (714) 850-1935 -- Copyright © 2000

Democrats and Republicans on Capitol Hill say that a change to current federal size and weight law soon is unlikely. However, the trucking industry gained some recent concessions, such as obtaining weight-limit exceptions for hauling certain types of cargo in Iowa, Nebraska, Maine, and New Hampshire. In May 1999, Reps. Collin Peterson (D-Minn.) and Merrill Cook (R-Utah) proposed a bill, HR 1667, that would allow states to increase the truck weight limit to 97,000 pounds. At press time passage of the bill this session was considered unlikely.


Why the trucking industry interest in LCVs? Money. A 1992 industry report, "Longer Combination Vehicles: Guide to Operation and Regulation," claims that using LCVs achieves "higher productivity with affordable capital outlay and without additional drivers." Depending on the configuration and cargo, an LCV can increase productivity by 35 to 100 percent and boost the total weight and cargo volume by about 50 percent.

With triples, two drivers can do the work of three; with turnpike doubles, two can do the work of four. "Most companies pay the driver one or two cents a mile more to haul a third trailer," says Bob Peterson, a business agent for Teamsters Local 162 in Portland, Oregon. The costs in fees and taxes are also typically fairly low. "But the trailer could generate $2,000 to $2,500 or more in shipping revenue," Peterson says.

The industry also argues that heavier trucks are more efficient because they use less fuel per pound than lighter ones. Fuel consumption increases as gross vehicle weight increases, but not in a linear fashion. So an LCV can haul considerably more cargo without using much more gas.

Presumably, cost savings to the trucking industry could mean lower retail prices for consumers. But the industry study cites only the indirect benefit of a gain in "productivity," with no direct promise of lower prices at, say, your local grocery or home-builder supply store.


LCVs can impose great damage on the nation's highways and, more importantly, they raise concerns for the safety of the people buckled into cars in the lanes next to them.

Although the United States has one of the best highway systems in the world, even the best roads eventually wear out. Other things being equal, pavement life is largely a function of the weight and size of the vehicles that use it, or, in the words of the U.S. Department of Transportation's 1998 Draft Comprehensive Truck Size and Weight (TS&W) Study, "pavement deterioration increases with axle weight and with the number of axle loadings a pavement experiences." Anyone who's encountered ruts or uneven concrete sections in the right lanes of freeways knows the lanes didn't get that way from a succession of Honda Civics passing over them.

Frank McCullough, Ph.D., at the Center for Transportation Research at the University of Texas in Austin, has found that the damage done by just one pass of a tractor-trailer is equivalent to the damage done by 2,000 to 3,000 passenger vehicles. That damage increases exponentially: A 95,000-pound truck does two to three times the damage of an 80,000-pound truck. The ATA acknowledges that one 80,000-pound truck can cause the same damage as 800 to 1,000 cars.

The role trucks play in bridge wear is not as well understood but, the federal TS&W study states, "changes in [truck size and weight] limits may impact [the] safety margins [of bridges], possibly increasing the number of bridges that must be replaced. . . ." Increased damage to the highway system also creates unpleasant and potentially dangerous driving conditions for motorists, plus added wear and tear to passenger vehicles' shock absorbers, tires, and alignment.

The sheer size and unwieldiness of LCVs can cause highway damage too. Turnpike and Rocky Mountain doubles can't turn as sharply as standard tractor-trailers (a handling quirk known as offtracking), which can result in "greatly increased pavement- edge damage, roadside equipment damage, and a hazard to adjacent traffic," according to a seminal (and still valid) 1983 California Department of Transportation (Caltrans) study.

Expanding the use of LCVs would require reengineering and reconstructing many freeway on- and off-ramps. Caltrans also determined that modifications ranging "from restriping to new construction" would be needed for freeway rest areas if LCVs were permitted in California.

LCV handling and maneuverability problems are magnified off the interstates, in urban areas. At intersections Caltrans found that Rocky Mountain doubles required two full lanes and sometimes more to complete a left turn. That doesn't leave much room for passenger cars.

The Caltrans report concluded that "Further increases in truck combination size must be carefully evaluated with respect to the safety of the motoring public and possible damage to the highway system."


Last year in the course of reauthorizing federal transportation legislation, Congress provided $216 billion to improve the nation's highway and transit systems over the next six years. However, even this extra funding wouldn't cover the additional costs that expanded use of LCVs could impose: construction of wider lanes and intersections, longer and wider entrance and exit ramps, and passing and climbing lanes. The federal TS&W study estimates that to make these kinds of upgrades to accommodate increased use of Rocky Mountain doubles could cost as much as $1.6 billion; adapting for turnpike doubles could cost up to $4.1 billion.

If the states were to spend the estimated $154 billion needed to repair the nations' bridges, they'd have to add another $53 billion to make them sturdy enough for LCV use. Prohibiting LCVs, the study says, could slash $20 billion from bridge repair and replacement costs nationwide.

Many states don't have adequate funds to correct existing highway problems and some sources think big trucks aren't paying their fair share for highway upkeep now. According to the 1997 Federal Highway Cost Allocation Study Summary Report, as a group "combination [vehicles] still only pay 90 percent of their cost responsibility, and the heaviest combinations may only pay 60 percent of their highway costs."

Unless trucking companies pay the increased costs to accommodate LCVs, those costs will be passed on to citizens in the form of increased taxes, special assessments, or construction bonds for highways.


Just the thought of driving behind or next to a big truck makes most motorists nervous, because they're afraid of being injured or killed in a collision with one. Their fears are grounded in fact. According to the National Transportation Safety Board, large trucks in general are overrepresented in fatal car-truck crashes. They make up 3 percent of registered vehicles, travel 8 percent of total vehicle miles, but are involved in 13 percent of all crashes involving fatalities. In 1997 about 5,400 people nationwide were killed in crashes involving large trucks; 75 percent of the fatalities involved trucks weighing more than 26,000 pounds. When a truck and a car collide and a fatality occurs, 98 percent of the time a person in the car dies.

Illustrations by Tim Barker -- (714) 850-1935 -- Copyright © 2000


While safety issues about long-combination vehicles require further study, Washington motorists who encounter standard big rigs every day can take steps to share the road safely.

Motorists are often under the false impression that because truck drivers sit up high, they can see more of the road. In fact, compared with passenger vehicles, trucks have more blind spots (also called No Zones). A federal study found that 36 percent of car-truck crashes in 1997 took place in No Zones.

  • Side no zones: Never cruise alongside a truck. Trucks have blind spots along the left and right sides where your car disappears from view. A rule of thumb: If you can't see the truck driver's face in the side mirror, he or she can't see you. And even if the driver can see you, he or she may need to change lanes quickly if there's an obstacle ahead. You don't want to be in the way.

  • Rear no zone: Never tailgate a truck. Truck drivers can't see directly behind them, and if they have to come to a sudden stop, a tailgater will have nowhere to go. Again, to gauge the proper distance, make sure you can at least see the truck's side mirrors.

  • Front no zone: When you pass a truck, give it plenty of room. Trucks need twice as much space to stop as cars do, so in order to be safe, make sure you can see the entire truck in your rearview mirror before you pull back in front of it. And once you get there, don't slow down abruptly.

--Kristin Tilford

The prospect of introducing still larger, heavier trucks onto the nation's highways only increases public concern and fear, which is reflected in surveys: Nationally, two out of three AAA members oppose the expanded use of LCVs, and 85 percent of AAA Washington's members oppose triple-trailer combinations.

LCVs make up only a small percentage of the nation's truck fleet--about 2 percent, according to the ATA--so meaningful data about the types, frequency, and causes of crashes is scarce. Nevertheless, there are legitimate reasons for concern.

Most of the handling and maneuverability problems with turnpike and Rocky Mountain doubles occur at low speeds. At freeway speeds large doubles are generally stable-- when traveling in a straight line. However, if they need to make a sudden lane change, their greater size and weight make them hard to control, especially in bad weather or in the dark. "The longer the truck and the more trailers, the less control the driver has over that which follows, and the greater the chance of a tragedy occurring," says Rep. James Oberstar of Minnesota, the ranking Democratic member of the House Committee on Transportation and Infrastructure. "It's difficult enough to manage a 53- foot trailer, but when you have a second and possibly a third behind that, the driver cannot have the same feel for the road, the same sensitivity for what's happening."

Triple-trailer combinations frequently exhibit a serpentine motion, and the third trailer may sway sideways unnervingly as much as a foot each way. Caltrans tests noted "extended periods of constant whip and sway" on the open road for "more than 75 percent of total mileage of the test," despite good road conditions and the absence of wind.

"One day I picked up an empty third trailer," says the Teamsters' Peterson, who has several hundred thousand miles' experience driving triples. "It was all over the road--a foot out to the right and then to the left, then two feet out. This went on for 40 miles. And road conditions were dry and good." Factor fog or rain into this scenario and imagine the danger.

When it rains, LCVs expose motorists to increased splash and spray. A typical big rig throws up considerably more water than a passenger vehicle; now imagine doubling the overall length of the truck and adding eight tires. If you're traveling at 65 mph and pass a turnpike double traveling at 60, you could be blinded for 15 seconds, long enough not to see the cars in front of you if they slowed suddenly.


The greater length and weight of LCVs makes them incompatible with mixed-vehicle traffic, creating potential hazards for safe passing and merging. In the best of circumstances, the federal TS&W study says, safely passing an LCV can take 8 percent longer than passing a conventional big rig. Upping the risk factor: Standards for marking passing zones with double-yellow lines on two-lane roads were developed in the 1930s for cars passing cars, not for a car passing a 120-foot long truck combination.

Differences in the relative speed of vehicles can cause collisions. The TS&W study shows that when the speeds of two vehicles traveling the same direction on a highway vary by 10 mph, they're nearly four times as likely to collide as when they're traveling the same speed. When the speed differential is 20 mph, a crash is almost 16 times as likely to happen.

Because LCVs have difficulty maintaining speeds on uphill grades, they can create "rolling roadblocks." In some states 35-mph minimum speeds for LCVs are in force. But LCVs pulling grades in Oregon, for example, have been clocked at less than 20 mph. In the Caltrans test, LCVs went so slow on 5 percent grades that, on a four-lane freeway, other trucks pulled out into adjoining lanes to pass them and left only the far left lane clear for cars.


The trucking industry says that LCVs are safe because they are driven only on appropriate roads (mostly rural interstates) under optimal conditions using the best equipment and the most experienced drivers.

But history shows that it's difficult to restrict LCVs to rural interstates. Eventually there's pressure to bring them into urban areas (they now run on the freeways of downtown Portland at rush hour, for example). And at some point the big trucks may have to exit the freeway and make deliveries on local roads.

Green Lights at U.S. Borders

The North American Free Trade Agreement (NAFTA), enacted in 1992 to expand the markets for goods and services produced in the United States, Canada, and Mexico, requires efforts to standardize truck regulations among the three nations. As a result, main routes such as I-5 and U.S. 395 could see heavy increases in truck traffic in coming years.

This has raised concern that larger trucks could be running on U.S. highways. Canada, for example, allows trucks that weigh up to 137,500 pounds. Mark Edwards, AAA's managing director of traffic safety, summarizes the organization's concerns: "The NAFTA provisions may simply overload the country's ability--particularly the federal government's ability--to make sure we have safe trucks from other countries on our roads."


LCV drivers themselves are concerned about changing standards with respect to weather. When Oregon first approved the use of triple trailers in 1965, they were to run only on two interstate highways and in good weather. Gradually the number of routes increased, and the LCVs are now permitted to run in rain. Triple-trailer drivers are frequently pressured to continue in bad weather, the Teamsters' Peterson says.

Driver skill is crucial to the safe operation of LCVs. The Caltrans study concluded that "the viability of LCVs on mainline urban freeways depends almost exclusively on the skill and diligence of the driver." But, says Peterson, "Companies are having a difficult time finding qualified drivers now. If there was a large expansion of LCV use, it would be impossible to find enough qualified triple-trailer drivers."


Before changing the limits on truck size and weight, crucial factors must be considered. One is the billions of dollars that would be needed to repair and upgrade the country's highway network if LCVs were permitted on most of the nation's highways. An ever- increasing number of cars and trucks are vying for space on these highways. During the past 20 years, for example, the number of cars on American roads has nearly doubled, but few miles of new roads have been built to accommodate them.

However, the single overriding issue regarding LCVs is the safety of the nation's motorists. AAA believes that LCVs may pose a threat to motorist safety on our roads, especially if they are allowed to operate on more roads and in more states. It's imperative that the problem of truck safety be fully and accurately understood.

But it's not.

"We need to better understand the factors contributing to truck safety before we allow an almost unbridled development of truck size, complexity, and weight," says Mark Edwards, AAA's national managing director of traffic safety. "There's a lack of reliable, accurate data, and the statistics the industry uses, such as fatality rates per total vehicle miles traveled, don't tell us how to make trucks safer."

Indeed, in 1993 the U.S. General Accounting Office stated that the absence of mileage data specific to LCV configurations makes it impossible for most states to compare accident rates for LCVs with accident rates for single trailers. And a recent GAO Report on Truck Safety estimates that the states left unreported about 30 percent of the fatal crashes involving large trucks in 1997.

An in-depth, nationwide study of crashes between passenger vehicles and large trucks is necessary; such a comprehensive survey would guide Congress in making decisions about truck safety issues. Once thorough research is available, we can move forward to steadily improve truck safety.

Until trucks' involvement in crashes and the consequences for motorists' safety is clear, AAA will oppose increases in current size and weight standards for trucks.

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