May 2018

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  1. Is speeding a safety problem?

    Yes. In 2015, a total of 9,557 deaths, or 27 percent of all motor vehicle fatalities, occurred in speed-related crashes. Based on a nationally representative sample of police-reported crashes, speeding — defined as exceeding the speed limit, driving too fast for conditions or racing — was involved in 10 percent of property-damage-only crashes and 14 percent of crashes with injuries or fatalities. The National Highway Traffic Safety Administration (NHTSA) estimates that the economic cost of speed-related crashes is about $52 billion each year. Blincoe, L.J.; Miller, T.R.; Zaloshnja, E.; and Lawrence, B.A. 2015. The economic and societal impact of motor vehicle crashes, 2010 (revised). Report no. DOT HS-812-013. Washington, DC: National Highway Traffic Safety Administration.

    In a high-speed crash, a passenger vehicle is subjected to forces so severe that the vehicle structure cannot withstand the force of the crash and maintain survival space in the occupant compartment. Likewise, as crash speeds get very high, restraint systems such as airbags and safety belts cannot keep the forces on occupants below severe injury levels.

    Speed has a major impact on the number of crashes and injury severity. Elvik, R. 2005. Speed and road safety: synthesis of evidence from evaluation studies. Transportation Research Record 1908:59-69. Washington, DC: Transportation Research Board. It influences the risk of crashes and crash injuries in three basic ways:

    • It increases the distance a vehicle travels from the time a driver detects an emergency to the time the driver reacts.
    • It increases the distance needed to stop a vehicle once the driver starts to brake.
    • It increases the crash energy exponentially. For example, when impact speed increases from 40 to 60 mph (a 50 percent increase), the energy that needs to be managed increases by 125 percent.

    For practical reasons, there are limits to the amount of crash energy that can be managed by vehicles, restraint systems and roadway hardware such as barriers and crash cushions. The higher the speed, the higher the likelihood that these limits will be exceeded in crashes, limiting the protection available for vehicle occupants. To put this into perspective, note that the government runs crash tests for occupant protection at 30-35 mph — speeds considered to be severe impact speeds.

  2. How many drivers speed?

    The majority of drivers exceed posted speed limits on many different kinds of roads, but the problem is greatest on freeways and expressways. National surveys found that on freeways and interstates 48 percent of free-flow traffic in 2007 and 72 percent in 2009 exceeded posted speed limits. Huey, R.; De Leonardis, D.; and Freedman, M. 2012. National traffic speeds survey I: 2007. Report no. DOT HS-811-663. Washington, DC: National Highway Traffic Safety Administration. Huey, R.; De Leonardis, D.; and Freedman, M. 2012. National traffic speeds survey II: 2009. Report no. DOT HS-811-638. Washington, DC: National Highway Traffic Safety Administration. Fourteen percent of all vehicles traveling on limited-access highways exceeded posted speed limits by 10 mph or more during 2007. The percentage rose to 20 percent during 2009. On other types of roads, proportions of drivers exceeding speed limits fell slightly in 2009 compared with 2007. Still, 13 percent of vehicles on major arterials and 15 percent on minor arterials and collectors traveled at least 10 mph over posted speed limits during 2009.

    In a 2016 national telephone survey conducted by the AAA Foundation for Traffic Safety, nearly half of drivers said they had exceeded the speed limit by 15 mph on a freeway or by 10 mph on a residential street in the past month. AAA Foundation for Traffic Safety. 2017. 2016 traffic safety culture index. Washington, DC.

  3. Who speeds?

    A 2011 national telephone survey found that drivers who reported consistently exceeding speed limits by 15 mph on highways or by 10 mph on residential streets tended to be younger than non-speeders. Schroeder, P.; Kostyniuk, L.; and Mack, M. 2013. 2011 national survey of speeding attitudes and behaviors. Report no. DOT HS-811-865. Washington, DC: National Highway Traffic Safety Administration.  In a study of drivers on limited access highways, drivers exceeding posted limits by more than 14 mph were more often male and more often judged to be younger than 30. Preusser, D.F.; Lund, A.K.; Williams, A.F.; and Blomberg, R.D. 1988. Belt use by high-risk drivers before and after New York's seat belt use law. Accident Analysis and Prevention 20(4):245-50. An observational study conducted on roads with speed limits ranging from 40-55 mph compared drivers traveling at least 15 mph above posted speed limits with drivers of adjacent vehicles traveling no more than 5 mph above the speed limit. Williams, A.F.; Kyrychenko, S.Y.; and Retting, R.A. 2006. Characteristics of speeders. Journal of Safety Research 37(3):227-32. Speeders were younger than drivers in the comparison group and had more violations and crashes on their driving records.

    Although speeding is a problem among all driver age groups, the crashes and violations of young drivers are much more likely to be related to speeding than those of drivers of other ages. Williams, A.F.; Preusser, D.F.; Ulmer, R.G.; and Weinstein, H.B. 1995. Characteristics of fatal crashes of 16-year-old drivers: implications for licensure policies. Journal of Public Health Policy 16(3):347-60. A study in California found that the rate of speeding violations per mile traveled was at least 3 times as high for drivers 16-19 years old as it was for drivers 30 and older. Janke, M.K.; Masten, S.V.; McKenzie, D.M.; Gebers, M.A.; and Kelsey, S.L. 2003. Teen and senior drivers. Sacramento, CA: California Department of Motor Vehicles. In a 2011 national telephone survey, the percentage of drivers who reported having at least one speeding-related crash during the past five years was higher for the youngest drivers, those 16-20 years old, than for any other age group, even though the youngest drivers may not have been driving for all of the past five years.  Schroeder, P.; Kostyniuk, L.; and Mack, M. 2013. 2011 national survey of speeding attitudes and behaviors. Report no. DOT HS-811-865. Washington, DC: National Highway Traffic Safety Administration. 

    In all fatal crashes in 2015, male drivers were more likely to be speeding than female drivers. Twenty percent of male drivers involved in fatal crashes were speeding at the time of the crash, compared with 12 percent of all female drivers. In addition, the proportion of drivers that were speeding in fatal crashes decreased with increasing driver age. Thirty-two percent of male drivers ages 15-24 in fatal crashes were speeding at the time of the crash, compared with 27 percent of male drivers ages 25-34, 20 percent of male drivers ages 35-44, 15 percent of male drivers ages 45-54 and 7 percent of male drivers ages 75 and older.

  4. Isn't speed variation — not high speed — the real problem?

    No. Both variation and speed are important. Although research conducted in the 1960s on two-lane rural roads indicated that vehicles traveling much faster or much slower than average were more likely to be involved in crashes, involvement in severe crashes increased with speed. Solomon, D. 1964. Accidents on main rural highways related to speed, driver, and vehicle. Washington, DC: Bureau of Public Roads, US Department of Commerce. While less speed variation is associated with fewer crashes because it cuts down on passing maneuvers and lane changes, Transportation Research Board. 1984. 55: a decade of experience. Special Report 204. Washington, DC. Garber, N. J. and Ehrhart, A. A. 2000. Effect of speed, flow, and geometric characteristics on crash frequency for two-lane highways. Transportation research record 1717: 76–83. Washington, DC: Transportation Research Board. the risk of death and severe injury is a direct exponential function of speed, not speed differences.

    Many differences in travel speeds are unavoidable because of the slower speeds of turning or merging vehicles. Higher speeds of other vehicles exacerbate this problem. Besides, many crashes and nearly half of those resulting in occupant deaths are single-vehicle impacts in which differences in vehicle speeds play no role or only a minor one.

  5. What's the history of speed limit laws in the United States?

    Speed limit laws, which date to 1901, traditionally have been the responsibility of the states. In 1973 Congress responded to oil shortages by directing the U.S. Department of Transportation to withhold highway funds from states that did not adopt a maximum speed limit of 55 mph. Before that, speed limits on rural interstates in most states ranged from 65 to 75 mph, with the majority of states setting rural interstate speed limits of 70 mph. In urban areas, most states maintained 55 mph speed limits before the national maximum speed limit was established.

    By March 1974, all states adopted the 55 mph national maximum speed limit. Concerns about fuel availability and costs faded, however, and Congress in 1987 allowed states to increase speed limits on rural interstates to 65 mph.

    The National Highway System Designation Act of 1995 repealed the maximum speed limit, allowing states to set their own limits for the first time since 1974. Many states quickly moved to raise speed limits on both rural and urban interstates and freeways.

    There has been a trend toward higher speed limits on freeways and interstates in recent years. Currently, 22 states have maximum speed limits of 70 mph and 12 states (Arizona, Arkansas, Colorado, Kansas, Louisiana, Maine, Michigan, Nebraska, New Mexico, North Dakota, Oklahoma and Washington) have maximum speed limits of 75 mph on some portion of their roadway systems. On some sections of interstates in seven states (Idaho, Montana, Nevada, South Dakota, Texas, Utah and Wyoming) speed limits are 80 mph. In October 2012, a 41-mile stretch of Texas State Highway 130 opened with a speed limit of 85 mph.

  6. What was the effect of the national maximum speed limit of 55 mph?

    The National Research Council attributed 4,000 fewer fatalities to the decreased speeds in 1974 compared with 1973 and estimated that returning the speed limits on rural portions of the interstate highway system to pre-1974 levels would result in 500 more fatalities annually, a 20-25 percent increase on these highways. Transportation Research Board. 1984. 55: a decade of experience. Special Report 204. Washington, DC.

  7. How has abolishing the national speed limit affected speeds?

    Most states raised speed limits in response to the 1995 abolishment of the national maximum speed limit, and the higher limits were associated with immediate increases in travel speeds. Within one year after speed limits were raised from 55 to 70 mph on three urban freeways in Texas, the percent of passenger vehicles traveling faster than 70 mph increased from 15 to 50 percent; the percent exceeding 75 mph increased from 4 to 17 percent. Retting, R.A. and Greene, M.A. 1997. Traffic speeds following repeal of the national maximum speed limit. ITE Journal 67:42-46. On California urban freeways where speed limits were raised from 55 to 65 mph, the percent of motorists traveling faster than 70 mph increased from 29 to 41 percent.   Ten years after speed limits were raised from 65 to 75 mph on rural interstates, the proportion of passenger vehicles exceeding 80 mph tripled in Nevada and nearly tripled in New Mexico. Retting, R.A. and Teoh, E.R. 2008. Traffic speeds on interstates and freeways 10 years after repeal of national maximum speed limit. Traffic Injury Prevention 9(2):119-24. By comparison, declines in travel speeds were observed on urban freeways in California and Nevada where speed limits did not change and where there were large increases in traffic volume and development of surrounding areas.

    In 2006 Texas raised the daytime speed limit for passenger vehicles on segments of I-10 and I-20 from 75 to 80 mph. During the 16-month period following the speed limit increase, mean speeds of passenger vehicles on I-20 increased by 9 mph relative to the comparison road, where no speed limit change occurred and traffic speeds declined. On I-10 mean speeds increased by 4 mph relative to the comparison road. Retting, R.A. and Cheung, I. 2008. Traffic speeds associated with implementation of 80 mph speed limits on West Texas rural interstates. Journal of Safety Research 39(5):529-34.

    In 2007 the Institute monitored travel speeds on interstates in eight metropolitan areas. Insurance Institute for Highway Safety. 2008. Special issue: speeding. Status Report 43(1):1-7. On urban interstates in all eight metro areas, the average speed of passenger vehicles exceeded the limits. On suburban and rural interstates, average speeds were faster than the limits in half of the metro areas. The proportion of passenger vehicles exceeding 70 mph on urban interstates ranged from 1 percent in Denver and Tampa to 38 percent in Albuquerque, while the percentage exceeding 75 mph on suburban and rural interstates ranged from 6 percent in Los Angeles to 49 percent in Tampa. The same study examined segments of rural interstates located 30-50 miles outside three of the metro areas. Outside Atlanta, where limits were 70 mph, 19 percent of passenger vehicles exceeded 70 mph, and 3 percent surpassed 75 mph. Speeds were much faster on the Los Angeles intercity segment, where 86 percent of passenger vehicles surpassed the 70 mph limit and 35 percent traveled faster than 80 mph.

    Effective May 2008, Utah allowed the speed limit for all vehicles to exceed 75 mph on rural interstate highways. The first sections of roadway were changed to an 80 mph limit in January 2009, and more were added in November 2010 and October 2013. An Institute study evaluated the effects of the 2010 and 2013 increases. Hu, W. 2017. Raising the speed limit from 75 to 80 mph on Utah rural interstates: Effects on vehicle speeds and speed variance. Journal of Safety Research 61:83-92. The average passenger vehicle and large truck speeds were about 3 mph and 2 mph higher than would have been expected without the increase, respectively. The likelihood that a passenger vehicle was traveling over 80 mph was 122 percent higher than would have been expected without the increase.

  8. How has abolishing the national speed limit affected fatalities?

    Institute studies show that deaths on rural interstates increased 25-30 percent when states began increasing speed limits from 55 to 65 mph in 1987. Baum, H.M.; Wells, J.K.; and Lund, A.K. 1991. The fatality consequences of the 65 mph speed limits, 1989. Journal of Safety Research 22(4):171-7. Baum, H.M.; Lund, A.K.; and Wells, J.K. 1989. The mortality consequences of raising the speed limit to 65 mph on rural interstates. American Journal of Public Health 79(10):1392-5. Baum, H.M.; Wells, J.K.; and Lund, A.K. 1990. Motor vehicle crash fatalities in the second year of 65 mph speed limits. Journal of Safety Research 21(1):1-8. In 1989, about two-thirds of this increase — 19 percent, or 400 deaths — was attributed to increased speed and the rest to increased travel. 

    A 1999 Institute study of the effects of the 1995 repeal of the national maximum speed limit indicated this trend had continued. Farmer, C.M.; Retting, R.A.; and Lund, A.K. 1999. Changes in motor vehicle occupant fatalities after repeal of the national maximum speed limit. Accident Analysis and Prevention 31(5):537-43. The Institute estimated a 15 percent increase in fatalities on interstates and freeways in 24 states that raised speed limits. 

    A 2002 study also evaluated the effects of increasing rural interstate speed limits from 65 mph to either 70 or 75 mph. Patterson, T.L.; Frith, W.J.; Povey, L.J.; and Keall, M.D. 2002. The effect of increasing rural interstate speed limits in the United States. Traffic Injury Prevention 3(4):316-20. States that increased speed limits to 75 mph experienced 38 percent more deaths per million vehicle miles traveled than expected — an estimated 780 more deaths. States that increased speed limits to 70 mph experienced a 35 percent increase, resulting in approximately 1,100 more deaths. 

    A 2009 study examining the long-term effects of the 1995 repeal of the national speed limit found a 3 percent increase in road fatalities attributable to higher speed limits on all road types, with the highest increase of 9 percent on rural interstates. Friedman, L.S.; Hedeker, D.; Elihu, D.; and Richter, D. 2009. Long-term effects of repealing the national maximum speed limit in the United States. American Journal of Public Health 99(9):1626-31. The authors estimated that 12,545 deaths were attributed to increases in speed limits across the U.S. between 1995 and 2005. 

    A recent Institute study examined longer-term changes in 41 states. During 1993-2013, a 5 mph increase in the maximum state speed limit was associated with an 8 percent increase in fatality rates on interstates and freeways and a 4 percent increase on other roads. Farmer, C.M. 2017. Relationship of traffic fatality rates to maximum state speed limits. Traffic Injury Prevention 18(4):375-380. In total, there were an estimated 33,000 more traffic fatalities during these years than would have been expected if maximum speed limits in 1993 had remained in place.  In 2013 alone, there were approximately 1,900 additional deaths — 500 on interstates/freeways and 1,400 on other roads.

  9. How are speed limits established?

    State laws set maximum speed limits for each type of road (e.g., interstate highway, two-way undivided highway) and land use (urban or rural). Federal Highway Administration. 2009. Speed concepts: informational guide. Publication No. FHWA-SA-10-001. Washington, DC: U.S. Department of Transportation. Statutory maximum speed limits also can be established for special situations such as school zones. The posted speed limit for a particular road or section of a road can be below the maximum speed limit allowed, however, if the local or state agency in charge of the road decides a lower limit is warranted.

    A common approach in setting speed limits is to consider the 85th percentile speed in free-flowing traffic, which is the speed that 85 percent of vehicles are traveling at or below in free-flowing conditions. Speed limits are sometimes raised to conform with this number if drivers are commonly violating the posted limit. Traffic engineers also take into account such factors as roadside environment, roadway design, crash experience and the prevalence of pedestrians.

  10. Are speed limits based on the 85th percentile traffic speed appropriate?

    Not always. Advocates of this approach argue that it reduces the need for enforcement and, at the same time, reduces crash risk by narrowing variation among vehicle speeds. However, numerous studies of travel speeds have shown that 85th percentile speeds on rural interstate highways increased when speed limits were raised and then continued increasing. Retting, R.A. and Greene, M.A. 1997. Traffic speeds following repeal of the national maximum speed limit. ITE Journal 67:42-46. Retting, R.A. and Teoh, E.R. 2008. Traffic speeds on interstates and freeways 10 years after repeal of national maximum speed limit. Traffic Injury Prevention 9(2):119-24. Retting, R.A. and Cheung, I. 2008. Traffic speeds associated with implementation of 80 mph speed limits on West Texas rural interstates. Journal of Safety Research 39(5):529-34. Najjar, Y.M.; Stokes, R.W.; Russell, E.R.; Ali, H.E.; and Zhang, X. 2000. Impact of new speed limits on Kansas highway. Report no. K-TRAN: KSU-98-3. Topeka, KS: Kansas Department of Transportation. The 85th percentile is not a stationary point. It is, rather, a moving target that increases when speed limits are raised. If speed limits are raised to meet a current 85th percentile speed, a new, higher 85th percentile speed will likely result.

  11. Some claim that higher speed limits would reduce crashes. Is this true?

    No. Advocates of higher speed limits have claimed that research on speed variation indicates faster speeds are not hazardous. They cite David Solomon's research from the 1960s that seems to show an increase in crash likelihood among drivers traveling slower than the average speed and a minimum of crashes at 5-10 mph above the average speed. Solomon, D. 1964. Accidents on main rural highways related to speed, driver, and vehicle. Washington, DC: Bureau of Public Roads, US Department of Commerce. However, the speeds of the crash-involved drivers in these studies were based on self-reports, and drivers exceeding speed limits are likely to deliberately underestimate their speeds. Such underestimation can account for much of the apparent underinvolvement of moderately high-speed drivers in crashes. Later research found that simply removing the crashes involving intersections and turning maneuvers from the Solomon data eliminated the overinvolvement of slower drivers in crashes. West, L.B. and Dunn, J.W. 1971. Accidents, speed deviation, and speed limits. Traffic Engineering 41(10):52-5. More importantly, the Solomon research addressed only speed variation, not speed limits.

    More recent evidence indicates that raising speed limits may actually increase speed variation. An Institute study on the effects of the speed limit increase from 75 to 80 mph in Utah found that the speed variance increased relative to what would have been expected without the speed limit change. Hu, W. 2017. Raising the speed limit from 75 to 80 mph on Utah rural interstates: Effects on vehicle speeds and speed variance. Journal of Safety Research 61:83-92.

  12. Should trucks have lower speed limits than cars?

    Although there is no definitive research showing crash effects associated with posting lower (differential) speed limits for large trucks, many safety experts favor differential limits because large trucks require much longer distances than cars to stop. Lower speed limits for trucks make stopping distances of trucks closer to those of lighter vehicles. Slower truck speeds also allow passenger vehicle drivers to pass trucks more easily. And because on average, large trucks tend to go slower than passenger vehicles on expressways with uniform speed limits, Retting, R.A. and Teoh, E.R. 2008. Traffic speeds on interstates and freeways 10 years after repeal of national maximum speed limit. Traffic Injury Prevention 9(2):119-24. Hu, W. and McCartt, A.T. 2013. Raising the speed limit from 75 to 80 mph on a Utah rural interstate: effects on vehicle speeds. Arlington, VA: Insurance Institute for Highway Safety. Hu, W. 2017. Raising the speed limit from 75 to 80 mph on Utah rural interstates: Effects on vehicle speeds and speed variance. Journal of Safety Research 61:83-92. lower speed limits for trucks reflect a natural speed differential between larger trucks and passenger vehicles.

    Institute research published in 1991 found that lower speed limits for trucks on 65 mph highways reduced the proportion traveling faster than 70 mph without increasing variation among vehicle speeds. Baum, H.M.; Esterlitz, J.R.; Zador, P.L.; and Penny, M. 1991. Different speed limits for cars and trucks: do they affect vehicle speeds? Transportation Research Record 1318:3-7. The percentage of trucks traveling faster than 70 mph was twice as large in states with uniform 65 mph limits (14 percent in Arizona, 9 percent in Iowa) as it was in states with different passenger vehicle (65 mph) and large truck (55 mph) speed limits (4 percent in California, 3 percent in Illinois). 

May 2018

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  1. What devices and methods are used to enforce speed limits?

    Police officers must be able to accurately measure vehicle speeds. Methods vary, but most fall under the general types listed below.

    Radar: Radar is the primary method of speed enforcement in the United States. Radar guns aim an electromagnetic signal at a target vehicle and pick up the return signal reflected off the vehicle. The Doppler effect causes the frequency of the return signal to shift by an amount dependent on the relative speeds of the source of the original signal and the target. Speed radar devices measure the frequency of the reflected signal and compare it with the frequency of the original signal to determine the speed of the target vehicle. Radar is highly reliable and accurate. However, it can be difficult to pinpoint specific vehicles in heavy traffic, and some motorists use radar detectors to help them speed without getting caught.

    Laser: Laser devices, also known as LIDAR (light detection and ranging), use a time/distance calculation to measure speed. The devices aim a narrow band of light at the target vehicle and measure the time it takes to receive the reflected light. Because the speed of both the original light pulse and its reflection are traveling at the same speed (the speed of light), differences in the time it takes the transmitted light to strike the target vehicle and return can be used to calculate the speed of the vehicle. Lasers can pinpoint specific vehicles in heavy traffic. Devices to detect lasers have been marketed, but the narrowness of the laser beam reduces the likelihood that a laser detector can identify the beam in time to provide drivers with enough advance warning to slow down and avoid a ticket.

    VASCAR: VASCAR stands for visual average speed calculator and recorder. It uses a portable computer to accurately clock, calculate and display speed based on the time a vehicle takes to travel a known length of road.

    VASCAR provides an average speed measurement over a greater distance than is possible with radar. It enables police officers to identify specific speeding vehicles and can be used from patrol cars following speeders. VASCAR can detect speeding vehicles going in the opposite direction. When used correctly, it is very reliable. It emits no radiation, so it can't be picked up by radar detectors.

    Aerial speed measurement: Officers in light aircraft measure vehicle speeds based on the time it takes to travel between two or more pavement markings spaced a known distance apart. Information is transmitted to officers on the ground who then issue speeding citations.

    Aerial surveillance can provide very accurate speed measurements and allow officers to focus on the fastest vehicles, but it is costly and can be difficult to use in locations with high traffic volumes.

    Speed cameras: Most speed cameras measure the speed of a vehicle at a single spot. Fixed cameras use either radar or detectors embedded in the road surface to measure a vehicle’s speed. Mobile cameras are placed at the roadside in marked or unmarked police cars, containers, poles, etc., and use radar or laser to measure speeds. Some communities require mobile cameras to be manned. In either fixed or mobile systems, if a vehicle is traveling faster than a predetermined speed, the date, time, location and speed are recorded along with a photo of the vehicle.

    More recent technology can measure average speeds over a certain distance. In this case, cameras located at two or more points record time-stamped images of all vehicles that pass them. Automatic license-plate recognition is used to match individual vehicles so that average speeds between the two points can be calculated. Time-stamped pictures of speeding vehicles are used as evidence of speeding. Point-to-point speed cameras have been used to enforce speed limits in Australia and the United Kingdom.

  2. What are the advantages of speed cameras?

    Traffic volumes and the number of drivers have risen faster than the availability of officers whose routine duties include traffic law enforcement. In some jurisdictions, available traffic enforcement resources have declined as apprehension of violent criminals and homeland security efforts take priority. In addition, it may be difficult to observe speeds at the worst places and times. In congested areas, there may be no place to pull over violators without creating hazards.

    Automated speed enforcement can substantially reduce speeding on a wide range of roads. Institute studies of cameras on residential roads in Maryland, on a high-speed roadway in Arizona and on city streets in the District of Columbia found that the proportion of drivers exceeding speed limits by more than 10 mph declined by 70, 88 and 82 percent, respectively, six to eight months after cameras were introduced. Retting, R.A., Farmer, C.F. and McCartt, A.T. 2008. Evaluation of automated speed enforcement in Montgomery County, Maryland. Traffic Injury Prevention 9(5):440-5. Retting, R.A.; Kyrychenko, S.Y.; and McCartt, A.T. 2008. Evaluation of automated speed enforcement on Loop 101 freeway in Scottsdale, Arizona. Accident Analysis and Prevention 40(4):1506-12. Retting, R.A. and Farmer, C.M. 2003. Evaluation of speed camera enforcement in the District of Columbia. Transportation Research Record 1830:34-37. An Institute study in Montgomery County, Md., found that about 7½ years after the speed camera program began, the cameras were associated with a 10 percent reduction in mean speeds and a 59 percent reduction in the likelihood that a vehicle was traveling more than 10 mph above the speed limit on camera-eligible roads, almost all of which had cameras. Hu, W. and McCartt, A.T. 2016. Effects of automated speed enforcement in Montgomery County, Maryland, on vehicle speeds, public opinion, and crashes. Traffic Injury Prevention 17(S1):53-58.

     A 2010 review published by the Cochrane Collaboration, an international public health organization, examined 35 studies from various countries. The authors concluded that speed cameras--including fixed, mobile, overt and covert devices --cut average speeds by 1-15 percent and the percentage of vehicles traveling above the speed limits or designated speed thresholds by 14-65 percent compared with sites without cameras. Wilson, C.; Willis, C.: Hendrikz, J.K.; Le Brocque, R.; and Bellamy, N. 2010. Speed cameras for the prevention of road traffic injuries and deaths. The Cochrane Library 2010, Issue 10. Oxfordshire, England: The Cochrane Collaboration.

  3. Do speed cameras reduce crashes and crash injuries?

    Yes. An Institute study in Montgomery County, Md., found that speed camera enforcement was associated with an 8 percent reduction in the likelihood that a crash on a camera-eligible road was speeding-related and a 19 percent reduction in the likelihood that a crash involved an incapacitating or fatal injury. Hu, W. and McCartt, A.T. 2016. Effects of automated speed enforcement in Montgomery County, Maryland, on vehicle speeds, public opinion, and crashes. Traffic Injury Prevention 17(S1):53-58. A corridor approach, in which cameras were periodically moved along the length of a roadway segment, provided an additional 30 percent reduction in the likelihood that a crash involved an incapacitating or fatal injury over and above the effect of the cameras.

    In 2010, the Cochrane Collaboration reviewed 28 studies that reported the effect on crashes and found reductions of 8-49 percent for all crashes, 8-50 percent for injury crashes and 11-44 percent for crashes involving fatalities and serious injuries, in the vicinity of camera sites. Wilson, C.; Willis, C.: Hendrikz, J.K.; Le Brocque, R.; and Bellamy, N. 2010. Speed cameras for the prevention of road traffic injuries and deaths. The Cochrane Library 2010, Issue 10. Oxfordshire, England: The Cochrane Collaboration. Over wider areas, the review found reductions of 9-35 percent for all crashes, and 17-58 percent for crashes involving fatalities and serious injuries. Reviewed studies with longer duration showed that these trends were either maintained or improved with time.

  4. Are speed cameras used to ticket motorists going 1 or 2 mph faster than the speed limit?

    No. Speed cameras usually are programmed so they will not be activated unless a vehicle is traveling significantly faster than the posted limit — typically 10 or 11 mph faster, although in certain places such as school zones the tolerance may be lower.

  5. Are speed cameras widely used in the United States?

    During 2017, 142 U.S. communities in 14 states and the District of Columbia operated speed camera programs, up from only four Arizona and Utah communities in 1995. Peoria, Ariz., and Paradise Valley, Ariz., were the first two communities to implement speed cameras in 1987. Cameras are used statewide in highway work zones in Illinois, Maryland and Oregon.

  6. Does the public support the use of speed cameras?

    Telephone surveys conducted by the Institute in jurisdictions with speed-camera programs show a majority of drivers support them.

    A 2014 survey of 900 licensed drivers ages 18 and older residing in Montgomery County, Md., found that 62 percent of drivers favored automated speed enforcement on residential streets about 7½ years after camera ticketing began. Hu, W. and McCartt, A.T. 2016. Effects of automated speed enforcement in Montgomery County, Maryland, on vehicle speeds, public opinion, and crashes. Traffic Injury Prevention 17(S1):53-58. A 2017 national survey of drivers ages 16 and older indicated that 48 percent supported the use of speed cameras on residential streets. AAA Foundation for Traffic Safety. 2018. 2017 traffic safety culture index. Washington, DC.

    A 2012 IIHS survey of 801 District of Columbia residents found strong support for speed cameras. Cicchino, J.B.; Wells, J.K.; and McCartt, A.T. 2014. Survey about pedestrian safety and attitudes toward automated traffic enforcement in Washington, D.C. Traffic Injury Prevention 15(4):414-23. D.C. has used speed cameras since 2001. In the survey, 88 percent of residents said that speeding was a serious threat to their personal safety. Seventy-one percent of residents who had driven a car in D.C. in the past month and 90 percent of residents who had not driven supported speed cameras.

    In Scottsdale, Ariz., 63 percent of drivers surveyed prior to the start of automated enforcement said speed cameras should be used on an urban freeway where camera enforcement was planned. After speed cameras were operational, 77 percent of drivers supported their use. Retting, R.A.; Kyrychenko, S.Y.; and McCartt, A.T. 2008. Evaluation of automated speed enforcement on Loop 101 freeway in Scottsdale, Arizona. Accident Analysis and Prevention 40(4):1506-12.

  7. What other technologies are available to help reduce speeding?

    Roadside electronic signs that display vehicle speeds to warn drivers they are speeding may reduce speeds and crashes at high-risk locations. IIHS research found that mobile roadside speedometers can reduce speeds at the sites of the speedometers, as well as for short distances down the road. Casey, S.M. and Lund, A.K. 1993. The effects of mobile roadside speedometers on traffic speeds. Accident Analysis and Prevention  25(5):627-34. When used in conjunction with police enforcement, the effect of speedometers can last longer.

    Many in-vehicle technologies exist to help reduce speeding. Drivers can use a vehicle's cruise control settings to avoid traveling faster than the speed limit. Off-the-shelf navigation systems and cellphone applications combine information from global positioning system (GPS) satellites with digital maps that have speed limit data to provide real-time alerts to drivers when they speed.

    Some fleet owners use devices called top speed limiters to keep drivers from traveling above a maximum speed. Many of these devices work by plugging directly into vehicles' computer systems, monitoring vehicle speed, and then constricting the amount of fuel that flows through the throttle if the driver reaches the maximum set speed. Telematics devices that plug into a vehicle's computer may include GPS linked to speed limits so that managers can monitor drivers' speeding relative to posted limits and later provide feedback about their speeding.

  8. What is intelligent speed assistance?

    Intelligent speed assistance (ISA), sometimes also called intelligent speed adaption, describes a class of in-vehicle systems that provide information to the driver on their speed relative to the posted speed limit. ISA systems work with either GPS devices linked to speed limits or on-board sensors or cameras that "read" speed limit signs and then integrate speed limit data with vehicle speed in real time. ISA systems differ in how much control drivers have in deciding whether to speed. The least automated systems provide alerts to drivers. Biding, T. and Lind, G. 2002. Intelligent Speed Adaptation (ISA), Results of large-scale trials in Borlänge, Lidköping,Lund and Umeå during the period 1999-2002. Publication 2002:89 E. Swedish National Road Administration. A second approach is to introduce resistance to gas pedals, making it harder but still possible to speed. Varhelyi, A. and Makinen, T. 2001. The effects of in-car speed limiters: Field studies. Transportation Research Part C, 9, 191-211.  The most aggressive automated systems limit gas flow to engines so drivers can accelerate up to but not over the speed limit. Some manufacturers offer built-in top speed limiters that must be set manually, whereas some systems will automatically limit the top speed to the posted speed limit. Carsten, O.; Fowkes, M.; Lai, F.; Chorlton, K.; Jamson, S.; Tate, F.; and Simpkin, B. 2008. ISA-UK, Intelligent Speed Adaptation, Final Report. London, England: Department for Transport.  A fourth option is to give drivers incentives, such as auto insurance discounts, to slow down. Reagan, I. J.; Bliss, J.P.; Van Houten, R.; and Hilton, B.W. 2013. The effects of external motivation and real-time automated feedback on speeding behavior in a naturalistic setting. Human Factors 55(1), 218-30.

    During the past 25 years, field assessments have indicated significant reductions in speeding when driving with ISA. The largest research effort studied several thousand Swedish drivers using systems giving an advisory alert, pedal feedback or throttle constriction for more than a year. Researchers reported a decrease in speeding violations for each system. Biding, T. and Lind, G. 2002. Intelligent Speed Adaptation (ISA), Results of large-scale trials in Borlänge, Lidköping,Lund and Umeå during the period 1999-2002. Publication 2002:89 E. Swedish National Road Administration. A U.S. study indicated that the potential to earn a modest monetary incentive while driving with an alerting ISA system increased the percentage of time driving at or below the speed limit from 70 percent to 83 percent. Reagan, I. J.; Bliss, J.P.; Van Houten, R.; and Hilton, B.W. 2013. The effects of external motivation and real-time automated feedback on speeding behavior in a naturalistic setting. Human Factors 55(1), 218-30. European researchers have found large reductions in speeding over periods ranging from months to over a year. Carsten, O. 2012. Is intelligent speed adaptation ready for deployment? Accident Analysis and Prevention 48:1-3.

    The largest technical barriers to ISA are the accuracy and breadth of coverage of digital maps with speed limits for GPS-based systems and the need for frequent speed limit signs for the camera-based systems. Digital maps may not include local roads and aren't always updated with speed limit changes in a timely fashion, and the camera-based systems will not know the speed limit until the vehicle passes a speed limit sign.

    The European New Car Assessment Program (Euro NCAP), which provides vehicle safety ratings, includes ISA as one of the safety features that automakers can use to qualify vehicles for the Euro NCAP Advanced designation. Carsten, O. 2012. Is intelligent speed adaptation ready for deployment? Accident Analysis and Prevention 48:1-3. Several manufacturers offer optional advisory ISA systems for vehicles sold in the U.S., and ISA systems that limit gas flow to engines are available as options on a limited number of new vehicles. Manufacturers have begun to integrate camera-based speed limit recognition with cruise control to adjust the set speed based on the posted limit.

  9. What are radar detectors?

    Radar detectors are radio receivers tuned to the frequency range used by police radar guns. Radar detectors are bought and sold for the sole purpose of helping speeders avoid speeding tickets.

  10. What is the problem with radar detectors?

    Research shows that drivers with radar detectors consistently are overrepresented among the fastest speeders. Freedman, M.; Williams, A.F.; Teed, N.; and Lund, A.K. 1990. Radar detector use and speeds in Maryland and Virginia. Arlington, VA: Insurance Institute for Highway Safety. In a survey of users, more than half admitted to driving faster than they would without the devices. Opinion Research Corporation. 1988. A survey about radar detectors and driving behavior. Princeton, NJ.

    Institute research looked at interstate highway drivers with and without radar detectors who were suddenly exposed to police radar. Before exposure, vehicles with detectors were traveling significantly faster than those without detectors. By 1 mile past the radar, more than three-fourths of the vehicles with radar detectors were traveling at least 5 mph faster than the speed limit. Teed, N.; Lund, A.K.; and Knoblauch, R. 1993. The duration of speed reductions attributable to radar detectors. Accident Analysis and Prevention 25(2):131-7.

    Speeders ticketed by police in Charleston, South Carolina, using laser devices, which radar detectors can't pick up, were 4 times as likely to have radar detectors as motorists stopped by officers using conventional radar. Teed, N. and Lund, A.K. 1993. The effect of laser speed-measuring devices on speed limit law enforcement in Charleston, South Carolina. Accident Analysis and Prevention 25(4):459-63.

  11. Are there laws banning radar detectors?

    Since January 1994, the U.S. Department of Transportation has prohibited radar detector use in commercial vehicles involved in interstate commerce. Several states also ban many commercial vehicles, often large trucks and buses, from using the devices for intrastate commerce. Radar detectors are banned in all vehicles in Virginia and the District of Columbia.

  12. What is the logic behind banning radar detectors in large trucks?

    A total of 3,986 people were killed in crashes involving large trucks in 2016, and most of them were not truck occupants. High speeds increase the already-long distances required to stop a large truck and exacerbate the effects of size and weight differences between trucks and passenger vehicles, leading to more severe crashes.

    Institute research focusing on large trucks, conducted before the federal ban on radar detectors in trucks involved in interstate commerce, found that trucks often had radar detectors and that these trucks were more likely to be exceeding the speed limit. Institute researchers measured speeds and radar detector use in large trucks in 17 states in 1990 and found that more than half of all trucks, including half of trucks carrying hazardous materials, were using radar detectors. Trucks with radar detectors exceeded the speed limits more often than those without radar detectors. Teed, N. and Williams, A.F. 1990. Radar detector use in trucks in 17 states. Arlington, VA: Insurance Institute for Highway Safety. An earlier study in Virginia and Maryland showed that, on interstates with 65 mph speed limits, trucks using radar detectors were twice as likely as those not using detectors to travel at least 5 mph faster than the limit, and 3 times as likely to travel at least 10 mph faster. Freedman, M.; Williams, A.F.; Teed, N.; and Lund, A.K. 1990. Radar detector use and speeds in Maryland and Virginia. Arlington, VA: Insurance Institute for Highway Safety.