Q&A: Large trucks
- 1 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 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 size and 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 that are even bigger than western doubles are allowed to travel on some roads. These trucks, called longer combination vehicles, either have three trailers or 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.
- 2 Do large trucks have high crash rates?
On average, drivers of large trucks travel many more miles than passenger vehicle drivers, and a high proportion of those miles are on interstates, which are the safest roads. In 2010, large trucks accounted for 4 percent of registered vehicles and 14 percent of miles traveled. Federal Highway Administration. 2012. Highway statistics, 2010. Washington, DC: U.S. Department of Transportation. Per unit of travel, large trucks were involved in 1.1 fatal crashes per 100 million miles traveled in 2010, compared with 1.3 for passenger vehicles. Large trucks have a much lower rate per mile traveled of crashes resulting in nonfatal injuries or property damage only compared with passenger cars and light trucks.
- 3 Who dies in crashes involving large trucks?
In 2011, 3,373 people died in crashes involving large trucks. Sixteen percent of these deaths were truck occupants, 66 percent were passenger vehicle occupants and 16 percent were pedestrians, bicyclists, or motorcyclists. In fatal two-vehicle crashes involving a passenger vehicle and a large truck, 98 percent of the deaths were occupants of the passenger vehicles. Large trucks were involved in 10 percent of all motor vehicle crash deaths and 22 percent of passenger vehicle occupant deaths in multiple-vehicle crashes.
- 4 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 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, Stein, H.S. and Jones, I.S. 1988. Crash involvement of large trucks by configuration: a case-control study. American Journal of Public Health 78(5):491-8. but a study in Indiana found that doubles did not show increased crash risk except on roads with snow, ice or slush. Braver, E.R.; Zador, P.L.; Thum, D.; Mitter, E.L.; Baum, H.M.; and Vilardo, F.J. 1997. Tractor-trailer crashes in Indiana: a case study of the role of truck configuration. Accident Analysis and Prevention 29(1):79-96.
- 5 Who oversees large truck safety in the United States?
Two U.S. Department of Transportation agencies plus individual 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 personnel conduct roadside inspections of trucks and drivers to enforce federal rules for equipment, hours of service and vehicle maintenance and inspection. Federal and state personnel also conduct reviews of carriers' compliance with these regulations through an FMCSA program called Carrier Safety Assessment, or CSA. Carriers with high rates of crashes and inspection violations are subject to interventions including warning letters, offsite investigations, onsite investigations and suspensions of service.
- 6 Do truck drivers need special licenses?
Yes. Licensing drivers is a state matter, but since 1992, federal law requires states to meet 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 established testing, licensing and health standards for issuing CDLs. 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 or more passengers or if they transport hazardous materials. A national database of all CDL holders helps to deter truckers from using multiple state licenses to conceal their traffic convictions and also prevents disqualified drivers from being licensed.
- 7 Are there age restrictions on who is permitted to operate large trucks?
If large trucks cross state lines or carry hazardous materials, their drivers must be 21 or older. States can permit drivers ages 18-20 to operate large trucks within the state.
- 8 Are young truck drivers at higher risk of crashing?
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. Campbell, K.L. 1991. Fatal accident involvement rates by driver age for large trucks. Accident Analysis and Prevention 23(4):287-95. Christie, R. and Fabre, J. 1999. Potential for fast-tracking heavy vehicle drivers. Melbourne, Victoria: National Road Transport Commission. Blower, D.; Lyles, R.W.; Campbell, K.L.; and Stamatiadis, P. 1990. The Michigan heavy truck study. Lansing, MI: Michigan Office of Highway Safety Planning. Blower, D. 1996.The accident experience of younger truck drivers. Ann Arbor, MI: University of Michigan Transportation Research Institute. Frith, W.J. 1994. A case-control study of heavy vehicle drivers' working time and safety. Proceedings of the 17th Australian Road Research Board Conference, 17-30. Brisbane, Queensland: Australian Road Research Board.
- 9 Is driver fatigue a factor in truck crashes?
Yes. Institute research found that truck drivers behind the wheel for more than eight hours are twice as likely to crash. Jones, I.S. and Stein, H.S. 1987. Effect of driver hours of service on tractor-trailer crash involvement. Arlington, VA: Insurance Institute for Highway Safety. Truckers' long work hours cause sleep deprivation, disruption of normal sleep/rest cycles and fatigue. Insurance Institute for Highway Safety. 2000. Comment to the Federal Motor Carrier Safety Administration concerning proposed changes to commercial truck drivers hours-of-service rules. Docket no. FMCSA-1997-2350, August 4. Arlington, VA. Insurance Institute For Highway Safety. 2008. Comment to the Federal Motor Carrier Safety Administration concerning the interim final rule on hours of service for commercial truck drivers. Docket no. FMCSA-2004-19608. March 6, 2008. Arlington, VA. Institute researchers found that truck drivers reporting hours-of-service violations are more likely to report having fallen asleep behind the wheel during the past month. Braver, E.R.; Preusser, C.W.; Preusser, D.F.; Baum, H.M.; Beilock, R.; and Ulmer, R. 1992. Long hours and fatigue: a survey of tractor-trailer drivers. Journal of Public Health Policy 13(3):341-66. McCartt, A.T.; Hellinga, L.A.; and Solomon, M.G. 2008. Work schedules of long-distance truck drivers before and after 2004 hours-of-service rule change. Traffic Injury Prevention 9(3):201-10. Another study based on a national sample of large truck crashes found that a truck driver's hours-of-service violations and logbook violations resulting in the driver being placed out of service increased the likelihood that the truck driver would be determined to have precipitated the crash. Blower, D.; Green, P.E.; and Matteson, A. 2010. Condition of trucks and truck crash involvement: evidence from the large truck crash causation study. Transportation Research Record 2194: 21-28. The proportion of large truck crashes for which fatigue is a contributing factor is uncertain.
- 10 What are the current hours-of-service rules (work-hour limits) for truck drivers?
Truck drivers currently operate under FMCSA regulations that went into effect in January 2004. Under the rules, interstate commercial truck drivers are not allowed to drive for more than 11 hours or drive after 14 hours since starting a duty shift until they take a 10-hour break. Drivers can't 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 of driving in 7 days or 88 hours in 8 days.
Further modifications to the work rules took effect Oct. 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.
Federal courts overturned the rules in 2004 and again in 2007. In October 2009, FMCSA reached a court settlement with safety groups. Under the terms of the deal, FMCSA agreed to review and reconsider the rule.
In December 2011, the agency issued a final rule that kept most provisions intact. Drivers and carriers must comply as of July 1, 2013. Drivers can continue to spend as many as 11 hours a day on the road, and they can't go over 60 work hours during a 7-day period or 70 work hours during an 8-day period. Restarts still are allowed, but drivers can only take 1 every 7 days, or 168 hours, compared with the two restarts under current rules. FMCSA added a requirement that a restart must include two overnight rest periods from 1 to 5 a.m.
- 11 Have the new rules reduced fatigued driving?
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. McCartt, A.T.; Hellinga, L.A.; and Solomon, M.G. 2008. Work schedules of long-distance truck drivers before and after 2004 hours-of-service rule change. Traffic Injury Prevention 9(3):201-10.
- 12 How are hours-of-service rules enforced? Is compliance a problem?
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. Braver, E.R.; Preusser, C.W.; Preusser, D.F.; Baum, H.M.; Beilock, R.; and Ulmer, R. 1992. Long hours and fatigue: a survey of tractor-trailer drivers. Journal of Public Health Policy 13(3):341-66. McCartt, A.T.; Hellinga, L.A.; and Solomon, M.G. 2008. Work schedules of long-distance truck drivers before and after 2004 hours-of-service rule change. Traffic Injury Prevention 9(3):201-10. McCartt, A.T.; Hammer, M.C.; and Fuller, S.Z. 1997. Work and sleep/rest factors associated with driving while drowsy: experiences among long-distance truck drivers. Proceedings of the 41st Annual Conference of the Association for the Advancement of Automotive Medicine, 95-108. Des Plaines, IL: Association for the Advancement of Automotive Medicine. About a third of drivers interviewed by the Institute in 2003, 2004 and 2005 admitted to often or sometimes omitting hours from their logbooks. McCartt, A.T.; Hellinga, L.A.; and Solomon, M.G. 2008. Work schedules of long-distance truck drivers before and after 2004 hours-of-service rule change. Traffic Injury Prevention 9(3):201-10. Some truck drivers refer to logbooks as "comic books" because they are so easily falsified.
- 13 Can hours-of-service monitoring be improved?
Yes. Electronic onboard recorders 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 U.S. Department of Transportation in 1995 to require the installation and use of tamper-resistant electronic onboard recorders on commercial vehicles whose drivers are required to maintain written logbooks. Insurance Institute for Highway Safety. 1995. Petition to the Federal Highway Administration to require electronic onboard recording devices for motor carriers, August 3. Arlington, VA. The National Transportation Safety Board also has repeatedly recommended that such recorders be mandated. In 2000, FMCSA proposed to require these devices in all large trucks, but dropped the proposal from the work-hour rules that took effect January 2004. Under a final rule issued in April 2010, commercial truck and bus carriers must install electronic onboard recorders fleetwide if violations of hours-of-service rules are uncovered in 10 percent or more of fleet records during a single compliance review. This would represent a small fraction of carriers. The rule also established technical performance standards for recorders rather than a single design standard. In late 2010, FMCSA issued a final rule expanding the electronic onboard recorder requirement to all carriers that are required to use logbooks, but the rule was struck down in court due to concerns that the devices could be used to harass truck operators. As part of the transportation reauthorization bill, passed in July 2012, FMCSA has been directed by Congress to resolve the harassment issue and issue a rule mandating electronic onboard recorders for all carriers that are required to use logbooks.
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. McCartt, A.T.; Hellinga, L.A.; and Solomon, M.G. 2008. Work schedules of long-distance truck drivers before and after 2004 hours-of-service rule change. Traffic Injury Prevention 9(3):201-10.
- 14 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. In 2011, 2 percent of fatally injured large truck drivers had blood alcohol concentrations (BACs) 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. Federal Highway Administration. 1995. Random roadside drug and alcohol pilot program. Final report. Washington, DC: U.S. Department of Transportation. 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. Lund, A.K.; Preusser, D.F.; Blomberg, R.D.; and Williams, A.F. 1988. Drug use by tractor-trailer drivers. Journal of Forensic Sciences 33(3):648-61. In 1999, almost 3 percent of drivers of large trucks in nonfatal crashes tested positive for illicit drugs. Federal Motor Carrier Safety Administration. 2000. Results from the 1999 drug and alcohol testing survey. Washington, DC: U.S. Department of Transportation.
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. 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 reduces the odds that a truck driver involved in a fatal crash will have a positive BAC by 14 percent. Snowden, C.B.; Miller, T.R.; Waehrer, G.M.; and Spicer, R.S. 2007. Random alcohol testing reduced alcohol-involved fatal crashes of drivers of large trucks. Journal of Studies on Alcohol 68(5):634-40.
As part of the 2012 transportation reauthorization bill, FMCSA is required to create a national clearinghouse for positive drug and alcohol test results of commercial drivers. This clearinghouse will allow employers to check for previous positive test results when they screen applicant drivers.
- 15 Are radar detectors legal in large trucks?
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 because the only use for radar detectors is to evade speed limit enforcement.
- 16 Are large trucks prone to rolling over?
Yes. Their high centers of gravity increase the risk of rolling over, particularly on curved roadway segments, such as ramps. In 2011, 52 percent of deaths among occupants of large trucks occurred in crashes in which their vehicles rolled over.
Vehicle stability control systems may help to reduce this toll. These systems are designed to intervene when a truck's motion becomes unstable, possibly resulting in rollover, jackknife or other loss of control. Roll stability control (RSC) intervenes when lateral acceleration on the truck and/or trailer puts the truck at risk of rollover. Electronic stability control (ESC) incorporates roll stability with directional stability to prevent understeer or oversteer. Neither RSC nor ESC is currently required for large trucks in the United States, but NHTSA has proposed a rule that would mandate ESC on all new power units of combination trucks and some motor coaches.
Based on an analysis of crashes occurring during 2004-08, the Institute estimates that ESC has the potential to prevent or mitigate as many as 31,000 crashes involving large trucks each year, including up to 20 percent of moderate-to-serious injury large truck crashes and 11 percent of fatal large truck crashes. Jermakian, J. S. 2012. Crash avoidance potential of four large truck technologies. Accident Analysis and Prevention 49:338-46. NHTSA estimates that ESC on large truck tractors and large buses could prevent 40 to 56 percent of rollovers and 14 percent of loss-of-control crashes. Wang, J.S. 2011. Effectiveness of stability control systems for truck tractors. Report no. DOT HS-811-437. Washington, DC: National Highway Traffic Safety Administration.
- 17 Is defective equipment a factor in truck crashes?
Yes. In the late 1980s, Institute researchers examined crashes of large trucks in the state of Washington and found that tractor-trailers with defective equipment were twice as likely to be in crashes as trucks without defects. Jones, I.S. and Stein, H.S. 1989. Defective equipment and tractor-trailer crash involvement. Accident Analysis and Prevention 21(5):469-81. 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.
A recent study examined the role of defective equipment in crashes included in the Large Truck Crash Causation Study. The study gathered detailed information on a national sample of 2001-03 crashes involving an evident injury and at least one large truck. According to Blower et al., 2010, post-crash inspections of the trucks indicated that almost 55 percent had at least one mechanical violation, and almost 30 percent had at least one out-of-service condition. Of all equipment violations, violations in the brake (36 percent) and lighting (19 percent) systems were the most frequent. A truck with an out-of-adjustment brake condition was 1.8 times as likely to be the vehicle that precipitated the crash. In rear-end and crossing-path crashes, brake violations significantly increased the likelihood that the truck was the striking vehicle. Blower, D.; Green, P.E.; and Matteson, A. 2010. Condition of trucks and truck crash involvement: evidence from the large truck crash causation study. Transportation Research Record 2194: 21-28.
- 18 Are braking systems on large trucks as effective as passenger vehicle brakes?
Compared with passenger vehicles, stopping distances for trucks are much longer. On wet and slippery roads, there are even greater disparities between the braking capabilities of large trucks and cars.
Braking disparities can be aggravated by poor maintenance of truck braking systems. New large trucks must have automatic brake adjusters, visible brake adjustment indicators and antilock brakes. Antilock brakes, which keep wheels from locking during hard braking, improve driver control of trucks during emergency stops and reduce the likelihood of tractor-trailer jackknifing. Antilocks have been required on new tractors as of March 1997 and on new trailers, single-unit trucks and buses as of March 1998. A recent study found that antilocks did not increase brake-related maintenance and repair expenses. Allen, K. 2009. An in-service analysis of maintenance and repair expenses for the anti-lock brake system and underride guard for tractors and trailers. Report no. DOT HS-811-109. Washington, DC: U.S. Department of Transportation.
In July 2009, NHTSA issued a final rule decreasing the maximum stopping distances for air-braked trucks by 30 percent. The rule went into effect on Aug. 1, 2011, for three-axle tractors with a gross weight of 59,600 pounds or less. Two-axle tractors and tractors with a gross weight above 59,600 pounds must meet the reduced stopping distance requirements by Aug.1, 2013.
- 19 What crash avoidance systems are available for large trucks?
Several crash avoidance technologies have been developed for large trucks. To date, penetration of these technologies into the large truck fleet has been slow, but the technologies have the potential to substantially reduce large truck crashes. Based on crashes during 2004-08, the Institute examined the maximum potential crash reductions associated with each of four technologies: side view assist, forward collision warning/mitigation, lane departure warning/prevention and vehicle stability control. A combination of all four technologies could prevent or mitigate as many as 107,000 police-reported crashes each year, representing 28 percent of all crashes involving large trucks. The technology could prevent or mitigate as many as 12,000 nonfatal injury large truck crashes and 835 fatal large truck crashes each year. Stability control technology has the greatest potential for preventing or mitigating large truck crashes involving nonfatal or fatal injuries, while side view assist has the greatest potential for preventing large truck crashes of any severity. The actual crash reductions from these crash avoidance systems for large trucks are not yet known. Jermakian, J. S. 2012. Crash avoidance potential of four large truck technologies. Accident Analysis and Prevention 49:338-46.
- 20 What are truck underride crashes, and what can be done about them?
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 passenger vehicles estimated that underride occurred in half of these crashes. Of the underride crashes, 57 percent involved the front of the truck, 22 percent involved the rear and 20 percent the side. Braver, E.R.; Cammisa, M.X.; Lund, A.K.; Early, N.; Mitter, E.L; and Powell, M.R. 1997. Incidence of large truck-passenger vehicle underride crashes in the Fatal Accident Reporting System and the National Accident Sampling System. Transportation Research Record 1595:27-33.
A federal rule to upgrade the rear-impact guard standard for new trailers took effect in January 1998. Several types of trucks are exempt from the rule, including straight trucks, trucks with rear wheels set very close to the back of the trailer and various types of special-purpose trucks. In 2010, the Institute studied how guards built to comply with the federal standards are performing in real-world crashes and found many fail, allowing severe passenger vehicle underride and resulting in serious or fatal injury. Brumbelow, M.L. and Blanar, L. 2010. Evaluation of U.S. rear underride guard regulation for large trucks using real-world crashes. Report no. SAE 2010-22-0007. Proceedings of the 54th Stapp Car Crash Conference, 119-31. Warrendale, PA: Society of Automotive Engineers.
As a result of this research and some initial crash tests that confirmed the problem, the Institute petitioned the federal government to require stronger rear underride guards on large trucks and improve performance test procedures. Although the federal government hasn't yet responded to the petition, the most recent trailer models from major manufactureres already have guards that are much stronger than required under U.S. rules. Some improvement may be a result of a tougher standard that semitrailers in Canada have had to meet since 2007. Recent Institute crash tests show that these latest underride guards work well when passenger vehicles strike the center of the trailer's rear. Insurance Institute for Highway Safety. 2013. Underride guards on big rigs can be lifesavers, but most leave passenger vehicle occupants at risk in certain crashes. Status Report 48(2):1-5. However, trailers from 7 of the 8 largest manufacturers still do a poor job of preventing underride in crashes involving only a small portion of the truck's rear.
There is no requirement for front or side underride guards in the United States. European Union regulations have required front underride guards on large trucks since 2003. A 1998 Institute study of fatal truck crashes in Indiana found that 9 out of 44 front underride crashes might have been survivable in the absence of underride. Braver, E.R.; Mitter, E.L.; Lund, A.K.; Cammisa, M.X.; Powell, M.R.; and Early, N. 1998. A photograph-based study of the incidence of fatal truck underride crashes in Indiana. Accident Analysis and Prevention 30(2):235-43. Side underride guards could be even more effective. A 2012 Institute study found that in the US strong side underride guards have the potential to reduce injury risk in about three-fourths of cases where a passenger vehicle occupant sustained a serious injury from an impact with the side of a large truck. Brumbelow, M.L.. 2011. Potential benefits of underride guards in large truck side crashes. Traffic Injury Prevention 13(6):592-9. Equipping large trucks and trailers with strong side guards does present technical challenges that would need to be overcome in order to achieve this benefit.
- 21 Can trucks be made more visible to other drivers at night?
Yes, and 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. Morgan, C. 2001. Effectiveness of retroreflective tape on heavy trailers. Report no. DOT HS-809-222. Washington, DC: National Highway Traffic Safety Administration. A federal rule requires improved conspicuity — adding reflective sheeting or reflectors — for trailers manufactured after December 1993 and truck tractors manufactured after July 1, 1997. Effective December 2001, the U.S. Department of Transportation requires the enhanced markings on all trailers on the road, not just new ones.