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Auto and Road User Journal
May 28, 1997
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Q&A: Large Trucks
(This article is reproduced with permission from the Insurance Institute for Highway Safety.)

What is a large truck?

Large trucks weigh more than 10,000 pounds and can be either single-unit vehicles or combination vehicles consisting of a tractor pulling one or more trailers. In most states, the maximum permitted length for a single trailer is 53 feet. Trucks pulling two 28-foot trailers are known as twins or western doubles. Trucks even bigger than western doubles are allowed to travel on some of the nation's roads. These rigs, called longer combination vehicles, pull multiple trailers with a combined length exceeding 57 feet. They include tractors pulling two 48-foot trailers, one 48-foot trailer plus one 28-foot trailer, three 28-foot trailers, or other configurations.

Do tractor-trailers have high crash rates?

Tractor-trailers are involved in more fatal crashes per unit of travel than passenger vehicles - 2.9 compared with 1.9 per 100 million miles traveled in 1993- even though a much higher proportion of tractor-trailer miles are traveled on well-designed interstate highways. Tractor-trailers have a lower rate of nonfatal crashes resulting in injuries or property damage only, compared with passenger vehicles, but when comparisons are based on miles traveled on the same types of roads (toll roads) tractor-trailer rigs are involved in more crashes per mile than passenger vehicles.

Who dies in crashes involving large trucks?

About 4,800 people die each year in crashes involving large trucks and most of them aren't truck occupants. In fatal two-vehicle crashes involving passenger vehicles and large trucks, 98 percent of the deaths occur to the people in the passenger vehicles. Large trucks accounted for 3 percent of registered vehicles and 7 percent of vehicle miles traveled in 1994 but were involved in 11 percent of all 1995 passenger vehicle occupant deaths and in 21 percent of multiple-vehicle passenger vehicle occupant deaths.

Are multiple-trailer trucks more likely to crash than single-trailer trucks?

Multiple-trailer trucks have more handling problems than single-trailer trucks. In general, the additional points of connection contribute to greater instability, which can lead to jackknifing, overturning, and lane encroachments. But the relationship between multiple-trailer trucks and crash risk isn't firmly established. A study in Washington State found that doubles (tractors pulling two trailers) were two to three times as likely as other rigs to be in crashes, but another study in Indiana found that doubles didn't show increased crash risk except on roads with snow, ice, or slush. Doubles are often operated by drivers with good safety records working for large companies with active safety programs.

Who's responsible for overseeing large truck safety in the United States?

Two agencies of the U.S. Department of Transportation oversee large truck safety. The National Highway Traffic Safety Administration (NHTSA) sets standards for new truck equipment. The Federal Highway Administration oversees the safety of commercial vehicles involved in interstate commerce, and this agency's regulations cover equipment, licensing, hours of service, and vehicle inspections and maintenance. State officials regulate intrastate trucks.

Do truck drivers need special licenses?

National licenses have been required since 1992 for commercial vehicle operation. This requirement is intended to reduce the number of truckers using multiple state licenses to conceal the overall total of their traffic violations. Both interstate and intrastate commercial drivers must obtain such licenses if they operate trucks with gross vehicle weight ratings of 26,000 pounds or more, if they transport 16 or more passengers, or if they transport hazardous materials requiring placarding.

Is driver fatigue a factor in truck crashes?

Yes. Driver fatigue is associated with truck crashes. Research shows truck crash risk increases along with driver hours behind the wheel, crash risk is highest between midnight and 6 a.m., and night- and rotating-shift workers - truckers among them -are involved in significantly more crashes than others. The long hours truck drivers work cause sleep deprivation, circadian desynchronization, and fatigue. Institute research has found that truck drivers reporting hours-of-service violations were also 77 percent more likely to report having fallen asleep behind the wheel during the month before the interview.

What are work rules and who violates them?

Under federal hours-of-service regulations, interstate commercial drivers aren't allowed to drive more than 10 hours or work more than 15 hours before an 8-hour break. Drivers are limited to either 60 work hours during a 7-day period or 70 work hours during an 8-day period, but studies suggest that these work rules are commonly violated. A 1990 Institute study estimated that, on a 1,200-mile route from Washington State to Minnesota, more than half of the tractor-trailer drivers were in violation of hours-of-service regulations. When the Institute surveyed long-haul tractor-trailer drivers in four states in 1991, almost three-fourths of the respondents indicated they violated hours-of-service regulations. About two-thirds of them said they routinely drove or worked more than 60-70 hours. More than 25 percent reported working 100 hours or more per week, and 19 percent admitted to falling asleep at the wheel one or more times during the preceding month. The long hours driven by many truckers lead directly to problems in addition to fatigue - notably the use and abuse of stimulants.

How can violations of the hours-of-service rules be reduced?

All large trucks should be equipped with electronic onboard recording devices to improve enforcement of hours-of-service regulations. The Institute and five other organizations have petitioned the FHWA to require the installation and use of onboard computers. Commercial vehicle operators who are required to maintain written log books would be required to use the electronic devices to record vehicle travel time and speed. The National Transportation Safety Board also has repeatedly recommended that such recorders be required. Current regulations allow drivers to use written logbooks, which truck drivers call "comic books" because they are so easily falsified. Onboard computers reduce the opportunities for violating the rules because they automatically record when a truck is driven and its speed. Europe has required tachographs, which are non-electronic devices designed to record vehicle travel hours, for about 30 years. Tachographs can be more easily falsified than onboard computers, which should be on all large trucks involved in interstate commerce. There also should be greater emphasis on carrier and shipper accountability in setting realistic delivery schedules that can be met without speeding and driving excessive hours.

Is the use of alcohol and other drugs among truckers a big problem?

Alcohol is much less of a problem among truck drivers than among passenger vehicle drivers. Only 4 percent of all drivers of large trucks who were killed in crashes during 1995 had blood alcohol concentrations of 0.10 percent or more, compared with 35 percent of fatally injured passenger vehicle drivers. Less is known about drug use, but the Institute did examine this issue in 1986 and found that 29 percent of a random sample of tractor-trailer drivers had used drugs with potential for abuse. The drugs found were mostly over-the-counter stimulants and marijuana. This research figured prominently in the later decision to require routine drug testing of transportation workers. Follow-up research by the National Transportation Safety Board found that 33 percent of truck drivers killed in crashes tested positive for alcohol or other legal and illegal drugs. Federal regulations require carriers and shippers to test all commercial drivers for drugs before employment, after crashes, and on a random basis. Alcohol tests are required only after crashes and on a random basis. New alcohol test rules were issued in 1994 that place drivers out of service if they are found with any alcohol in their systems.

Are radar detectors legal in large trucks?

Radar detector use is banned in commercial vehicles involved in interstate commerce. The Institute and other organizations petitioned for such a regulation in 1988 and again in 1990 because the only use for radar detectors is to evade speed limit enforcement. FHWA issued the ban on detectors, effective in 1994, but is leaving enforcement up to the states.

Does defective equipment play an important role in truck crashes?

Yes. Institute researchers who examined crashes of large trucks in Washington state found that tractor-trailers with defective equipment are twice as likely to be in crashes as trucks without defects. Brake defects are most common. They were found in 56 percent of the tractor-trailers involved in crashes. Steering equipment defects were found in 21 percent of crash-involved trucks.

How effective are truck brakes?

Compared with passenger vehicles, stopping distances for trucks are much longer and the ability of truck drivers to control their rigs during emergency braking is limited. On wet and slippery roads there are huge disparities between the braking capabilities of large trucks and cars. Antilock brakes, which keep wheels from locking, improve driver control of trucks during emergency stops and reduce the likelihood of jackknife in tractor trailers. Current brake problems are aggravated by the poor maintenance practices of some truck companies. Out-of-adjustment brakes are the most common reason for authorities to order trucks out of service and are a factor in many truck crashes. New large trucks must have automatic brake adjusters and visible brake adjustment indicators.

Do all large trucks have antilock brakes?

NHTSA issued a rule in 1995 requiring antilock brakes on newly manufactured medium and heavy vehicles. They are scheduled to be on new tractors as of March 1997 and new trailers as of March 1998. Antilocks are required on all new trucks, buses, and trailers in Japan and the European Union.

What are truck underride crashes?

In underride crashes, an automobile slides partially or wholly under a truck or trailer, increasing likelihood of death or serious injury to the car occupants. The problem of fatal underride crashes has been substantially underestimated by NHTSA, according to Institute research. A 1996 Institute study of fatal crashes between large trucks and cars estimates that front, rear, or side underride occurred in half of these crashes. A federal rule was issued in early 1996 to upgrade the rear impact guard standard for trailers only. The rule takes effect in 1998. The new guard will prevent some of the deaths and injuries that occur in underride and other rear impact crashes, but the underride guard requirements should extend to single-unit trucks, as well.

Can trucks be made more visible to other drivers at night?

During the day, trucks are easy to see, but it's a different story at night. Research indicates that, if drivers of other vehicles could recognize medium and heavy trucks more easily, they would be able to gauge their speed and distance more accurately and respond sooner when necessary. Consequently, some nighttime crashes would be prevented while the severity of others might be reduced. Federal studies estimate that enhancing the conspicuity of trailers would reduce by 15 percent the incidence of crashes in which trailers are hit from the side or rear. A federal rule requires improved conspicuity - adding reflective sheeting or reflectors - for trailers manufactured after December 1993 and truck tractors(bobtails) manufactured after July 1, 1997. FHWA is considering a proposal to require the enhanced marking for all trailers on the road, not just new ones.


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