Large trucks weigh more than 10,000 pounds and can be either single-unit vehicles or combination vehicles consisting of a single-unit truck or tractor pulling one or more trailers. The federal commercial vehicle maximum weight standard on the interstate highway system is 80,000 pounds gross vehicle weight, unless a higher maximum weight existed on the state level before July 1, 1956. Off the interstate highway system, states may set their own commercial vehicle weight standards. In most states, the maximum permitted length for a single trailer is 53 feet. Tractors 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 trucks, called longer combination vehicles, either have three trailers or have at least two, one of which is 29 feet or longer, or the tractor and two trailers have a combined weight exceeding 80,000 pounds. Longer combination vehicles are prohibited in many states and are allowed only in states that permitted them prior to June 1, 1991.

On average, drivers of large trucks travel many more miles than passenger vehicle drivers. In 2006, large trucks accounted for 4 percent of registered vehicles and 7 percent of miles traveled.¹ Per unit of travel, large trucks are involved in more fatal crashes than passenger vehicles — 2.0 compared with 1.7 crashes per 100 million miles traveled in 2006. The disparities between large trucks and passenger vehicles vary by specific vehicle type, with cars having the lowest fatal crash rate (1.4) and tractor-trailers having the highest rate (2.3). The higher fatal crash rate for large trucks occurs although much higher proportions of their miles are traveled on interstate highways, which are the safest roads. The higher fatal crash rate is attributable to the size disparity between large trucks and passenger vehicles. Large trucks have a much lower rate per mile traveled of nonfatal crashes resulting in injuries or property damage only compared with passenger cars and light trucks.²

About 5,000 people die each year in crashes involving large trucks, and 84 percent of them are not truck occupants. In fatal two-vehicle crashes involving passenger vehicles and large trucks, 98 percent of the deaths occur to the occupants in the passenger vehicles. Large trucks accounted for 4 percent of registered vehicles and 7 percent of vehicle miles traveled in 2006¹ but were involved in 11 percent of all motor vehicle crash deaths.

Multiple-trailer trucks have more handling problems than single-trailer trucks. In general, the additional connection points contribute to greater instability, which can lead to jackknifing, overturning, and lane encroachments. But the relationship between multiple-trailer trucks and crash risk is not 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,³ but a study in Indiana found that doubles did not show increased crash risk except on roads with snow, ice, or slush.⁴ One mitigating factor may be that doubles often are operated by drivers with good safety records working for large companies with active safety programs.

Two agencies of the US Department of Transportation and the states oversee large truck safety. The National Highway Traffic Safety Administration (NHTSA) sets standards for new truck equipment and has some jurisdiction over equipment standards for trucks currently on the road. The Federal Motor Carrier Safety Administration (FMCSA) oversees the safety of commercial vehicles in interstate commerce (vehicles operating across state lines). FMCSA regulations cover equipment, licensing, hours of service, and vehicle inspection and maintenance. States regulate intrastate trucks (trucks operating only within a single state's borders), and state inspectors are the primary enforcers of the federal rules for equipment, hours of service, and vehicle maintenance and inspection.

Yes. Although states have issued the licenses since 1992, federal law requires states to meet uniform licensing standards for commercial driver's licenses (CDLs). Prior to 1992, a few states allowed any driver licensed to drive an automobile to drive a large truck or bus, and other states had weak testing and licensing standards for commercial drivers. Since 1992, federal law has required CDLs to drive commercial motor vehicles and has established testing and licensing standards for issuing these licenses. Both interstate and intrastate commercial drivers must obtain such licenses if they operate trucks with gross vehicle weight ratings of 26,001 pounds or more, if they transport 16 passengers or more, or if they transport hazardous materials. A driver holding a CDL is entered into a national database. This requirement is intended to ensure that truckers do not use multiple state licenses to conceal the overall total of their traffic convictions.

If large trucks cross state lines or if they carry hazardous materials, their drivers must be 21 or older. States can permit drivers ages 18-20 to operate large trucks only within the state.

Yes. Studies conducted in Australia, New Zealand, and the United States indicate that truck drivers younger than 21 and in their 20s have a higher rate of involvement in both fatal and nonfatal crashes than older drivers.⁵

Yes. Institute research found that truck drivers behind the wheel for more than 8 hours had a twofold increase in crash risk.⁶ Crash risk also is higher between midnight and 6 am. Truckers' long work hours cause sleep deprivation, disruption of normal sleep/rest cycles, and fatigue.⁷ The Institute found that truck drivers reporting hours-of-service violations were more likely to report having fallen asleep behind the wheel during the past month.^8,9 The proportion of large truck crashes for which fatigue is a contributing factor is uncertain.

In January 2004, FMCSA implemented new hours-of-service regulations for truck drivers, increasing the required daily off-duty period but also increasing daily and weekly allowable driving times. Under the current rules, interstate commercial truck drivers are not allowed to drive more than 11 hours or drive after 14 hours since starting a duty shift until they have a 10-hour break. Drivers cannot drive after accruing 60 work hours during a 7-day period or 70 work hours during an 8-day period, but a "restart" provision allows truckers to get back behind the wheel after 34 hours off duty. Using this provision, a driver may log up to 77 hours in 7 days or 88 hours in 8 days.

Further modifications to the work rules took effect October 1, 2005. These revisions provide that drivers who use sleeper berths in their trucks may split the required minimum 10-hour daily off-duty period into a period of at least 8 hours in the sleeper berth and a period of at least 2 hours in the sleeper berth or off duty. Short-haul truckers may extend their work day twice a week, and these drivers are exempt from a requirement to carry a logbook of their hours of work.

No. Based on Institute surveys of long-distance truck drivers in two states (Pennsylvania and Oregon), drivers are spending more hours behind the wheel since the work rules changed in January 2004. They also report more instances of falling asleep at the wheel. In Pennsylvania, 19 percent of truck drivers admitted to dozing at the wheel at least once during the past month in 2005, up from 13 percent in 2003, under the old rule. The proportions in Oregon were 21 percent in 2005 compared with 12 percent in 2003.⁹

Current regulations allow truck drivers to record their hours in written logbooks that are reviewed by inspectors. Studies of long-distance truck drivers have found that work rules commonly are violated.^9,10 About a third of drivers interviewed by the Institute in 2003, 2004, and 2005 admitted to often or sometimes omitting hours from their log books.⁹ Some truck drivers refer to logbooks as "comic books" because they are so easily falsified.

Onboard computers reduce opportunities for violating the rules because they automatically record when a truck is driven. Beginning in the 1980s, Europe required mechanical (nonelectronic) tachographs, designed to record vehicle travel hours. Mechanical tachographs can be falsified more easily than onboard computers, so as of May 2006, new trucks and intercity buses registered in the European Union must be equipped with electronic recording devices.

The Institute and five other organizations petitioned the US Department of Transportation in 1995 to require the installation and use of tamper-resistant electronic onboard computers on commercial vehicles whose drivers are required to maintain written logbooks.¹¹ The National Transportation Safety Board also has repeatedly recommended that such recorders be mandated. In 2000, FMCSA published a proposal to require these devices but dropped the proposal from the work-hour rules that took effect January 2004. In January 2007, FMCSA proposed to require electronic onboard recorders for only the worst habitual violators of the hours-of-service rules. The agency would require only a tiny fraction of carriers to install recorders, even though Institute surveys show many drivers and carriers violate the rules.⁹ FMCSA has not published a final rule.

A large number of trucks already are equipped with onboard recorders. About 45 percent of the long-distance truck drivers interviewed by the Institute in 2005 said their trucks had electronic onboard recorders, up from about 18 percent in 2003 and 38 percent in 2004. Of the drivers who reported having recorders, only 10 percent or fewer said they used them in lieu of paper logbooks to show compliance with the work rules.⁹

Alcohol is much less of a problem among truck drivers than among passenger vehicle drivers. In 2006, 5 percent of fatally injured large truck drivers had blood alcohol concentrations (BAC) at or above 0.08 percent, compared with 33 percent of fatally injured passenger vehicle drivers. A 1995 roadside study in four states found that illicit drugs such as marijuana, cocaine, or amphetamines/methamphetamines were more prevalent than alcohol. Almost 5 percent of truck drivers tested positive for illicit drug use but only 0.2 percent tested positive for alcohol.¹² This study did not test for use of legal over-the-counter stimulants, which were present in 12 percent of truck drivers in an earlier Institute study.¹³ In 1999, almost 3 percent of drivers of large trucks in nonfatal crashes tested positive for illicit drugs.¹⁴

Federal regulations require carriers to test all commercial drivers for drugs before employment, after crashes, and on a random basis. Alcohol tests are required after crashes and on a random basis. New alcohol test rules, issued in 1994, place drivers out of service if they are found with any alcohol in their systems, and those who are found with BACs at or above 0.04 percent are disqualified from driving with a CDL. Random alcohol testing has been found to reduce the odds that a truck driver involved in a crash will have a positive BAC by 14 percent.¹⁵

A recent report by the US Government Accountability Office (GAO) recommended that a national clearinghouse for positive drug and alcohol test results of commercial motor vehicle drivers be created. This would enable employers to be aware of previous positive test results when they screen applicant drivers.¹⁶

Since 1994, federal regulations have banned radar detector use in commercial vehicles involved in interstate commerce. The Institute and other organizations petitioned for this regulation in 1988 and again in 1990 because the only use for radar detectors is to evade speed limit enforcement.

Yes. Their high centers of gravity increase the risk of rolling over, particularly on curving ramps. In 2006, 53 percent of deaths among occupants of large trucks occurred in crashes in which their vehicles rolled over, compared with 59 percent of SUV occupant deaths and 48 percent of pickup occupant deaths (both SUVs and pickups also have high centers of gravity). In contrast, 25 percent of car occupant deaths occurred in vehicles that rolled over.

Electronic stability control (ESC) systems are designed to continuously monitor how well a vehicle is responding to a driver's input. When the sensors detect the vehicle is straying from the driver's intended line of travel, ESC brakes individual wheels and modulates engine power to help the driver maintain control of the vehicle. ESC systems in large trucks can utilize the tractor and/or trailer brakes depending on the situation. In Institute studies, ESC has been found to reduce fatal single-vehicle crash risk by 56 percent and fatal multiple-vehicle crash risk by 32 percent for cars and SUVs.¹⁷ The impact of ESC on large truck crashes and rollovers is not known.

In the late 1980s, Institute researchers examined crashes of large trucks in Washington state and found that tractor-trailers with defective equipment were twice as likely to be in crashes as trucks without defects.¹⁸ Brake defects were 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. More current estimates of the crash risk associated with defective equipment are not available.

Compared with passenger vehicles, stopping distances for trucks are much longer. On wet and slippery roads, there are greater disparities between the braking capabilities of large trucks and cars. In December 2005, the National Highway Traffic Safety Administration proposed a rule reducing the maximum stopping distance for trucks by 20 to 30 percent, a decrease obtainable with existing technologies. A final rule has not been published.

Brake problems are aggravated by poor maintenance. Out-of-adjustment brakes are the most common reason for authorities to order trucks out of service.¹⁹ New large trucks must have automatic brake adjusters, visible brake adjustment indicators, and antilock brakes. Antilock brakes, which keep wheels from locking, improve driver control of trucks during emergency stops and reduce the likelihood of tractor-trailer jackknife.

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

In an underride crash, a passenger vehicle goes partially or wholly under a truck or trailer, increasing the likelihood of death or serious injury to the passenger vehicle occupants. A 1997 Institute study of fatal crashes between large trucks and cars estimated that front, rear, or side underride occurred in half of these crashes.²⁰ A federal rule to upgrade the rear impact guard standard for new trailers took effect in January 1998. The improved guard should prevent many of the deaths and injuries that occur in rear impact crashes.

Underride guards prevent many of the deaths and injuries that occur in rear impact crashes

During the day trucks are easy to see, but it is a different story at night. Research indicates that when drivers of other vehicles can recognize medium and heavy trucks more easily, they can gauge the trucks' speed and distance more accurately and react sooner when necessary. Federal studies have reported that enhancing the conspicuity of trailers reduced the incidence of crashes in which trailers were hit from the side or rear at night on unlighted roads.²¹ 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. Effective December 1, 2001, the US Department of Transportation requires the enhanced markings on all trailers on the road, not just new ones.

Reflective markings improve the conspicuity of trucks at night

Canadian trucks are allowed to deliver loads from Canada and pick up loads with a Canadian destination, but generally cannot pick up US loads with a US destination. Most Mexican trucks are restricted to border cities, but the US government plans to permit Mexican motor carriers the same access to the United States as Canadian motor carriers, provided they meet safety and insurance requirements. Currently, only a few approved carriers can drive beyond the restricted border cities. A three-year demonstration project began in September 2007 to allow up to 100 Mexican trucking companies to operate long-haul within the United States. The trucks from these approved carriers can transport freight between Mexico and the US but are not authorized to make deliveries between US cities. The trucks must satisfy all US safety requirements and are inspected every time they are permitted to cross the border and travel beyond the border cities.

Data on the crash experience of Mexican trucks are insufficient to determine if they have a higher crash risk than US trucks. Past safety inspection data indicate that out-of-service rates for Mexican trucks were lower in California, a state with a stringent inspection program, than in three other border states with less frequent inspections.²² However, within the past few years, more safety inspectors have been hired, border inspection facilities have been improved, and the number of inspections of Mexican trucks within the southern border zones has increased substantially. The rate of Mexican trucks placed out of service for vehicle safety violations also has declined.²³