Speed

More than 12,000 deaths — 29% of all crash fatalities — occurred in speed-related crashes in 2022. High speeds make a crash more likely because drivers have less time to react and because it requires a longer distance to stop or slow down. They also make collisions more deadly because modest increases in speed cause large increases in crash energy.

Raising speed limits leads to more deaths. People often drive faster than the speed limit, and if the limit is raised, they will go faster still. Research shows that when speed limits are raised, speeds go up, as do fatal crashes. By the same token, lowering speed limits cuts injury crashes.

Speed safety cameras are an important tool. Numerous studies have shown that cameras reduce speeds and crashes on all types of roads.

Speed has a major impact on the number of crashes and the severity of injuries they cause (Elvik, 2005). It influences the risk of crashes and crash injuries in four 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 risk that an evasive steering maneuver will result in loss of control.
• It increases crash energy disproportionately. For example, when impact speed increases from 40 to 60 mph (a 50% increase), the energy that needs to be managed increases by 125%. This additional energy needs to be absorbed and dissipated, challenging the vehicle structure and increasing the likelihood of severe injuries.

In a high-speed crash, a passenger vehicle is subjected to forces so severe that the vehicle structure cannot withstand the stress 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.

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.

Some people contend that speed variation, not speeding, is the real danger. This idea is rooted in research conducted in the 1960s on two-lane rural roads, which found that vehicles traveling much faster or much slower than average were more likely to be involved in crashes (Solomon, 1964). However, that same research found that involvement in severe crashes increased with speed.

While less speed variation is associated with fewer crashes because it cuts down on passing maneuvers and lane changes (Garber & Ehrhart, 2000; Transportation Research Board, 1984), the risk of death and severe injury is directly related to the speed at the time of a crash, not the speed difference between vehicles.

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 speeds between vehicles play no role or only a minor one.

In 2022, a total of 12,151 deaths, or 29% 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 8% of property-damage-only crashes and 12% of crashes with injuries or fatalities in 2022.

The National Highway Traffic Safety Administration (NHTSA) estimates that the economic cost of speed-related crashes was about $46 billion in 2019 (Blincoe et al., 2023).

Speeding has become both more common and more extreme since the start of the COVID-19 pandemic in 2020. NHTSA reported in 2021 that the difference in speed between the fastest 1% of vehicles and the slowest 1% significantly narrowed on urban interstate freeways after March 2020 compared with 2019, from approximately 10 mph to less than 5 mph (Office of Behavioral Research, 2021). The speed of the fastest 1% of vehicles was higher through the first six months of 2021 than during 2019 on urban and rural interstate freeways and on urban major collectors.

Similarly, IIHS researchers found that the percentage of drivers exceeding the speed limit by at least 5 and 10 mph increased on Virginia roads during March-June 2020 compared with the same months during the prior year (Wang & Cicchino, 2023). 

In a 2022 national telephone survey conducted by the AAA Foundation for Traffic Safety, 49% of drivers said they had exceeded the speed limit by 15 mph on a freeway in the past month, and 35% reported exceeding the speed limit by 10 mph on a residential street (AAA Foundation for Traffic Safety, 2023).

Drivers who speed tend to be younger than drivers who don’t, and male drivers are more likely than female drivers to speed (Preusser et al., 1988; Schroeder et al., 2013; Williams et al., 2006).

These trend holds true for fatal crashes involving speeding. Twenty percent of male passenger vehicle drivers involved in fatal crashes were speeding at the time of the crash in 2022, compared with 12% of female drivers. The proportion of drivers that were speeding in fatal crashes decreased with increasing driver age.

Speed limit laws, which date to 1901, traditionally have been the responsibility of the states, but the national maximum speed limit in place in the 1970s and 1980s effectively established maximum speed limits of 55 mph everywhere in the country. Since its complete repeal in 1995, speed limits have trended up.

Currently, 22 states have maximum speed limits of 70 mph, and 11 states have maximum speed limits of 75 mph on some portion of their roadway systems. On some sections of interstates in eight states, 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.

Maximum posted speed limits for different road types, by state

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). 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.

To set speed limits for specific roads, traffic engineers for decades relied heavily on the 85th percentile speed, which is the speed that 85% of vehicles are traveling at or below in free-flowing conditions. Recent work has highlighted the importance of other factors, such as roadway design and context, as well as the prevalence of pedestrians and bicyclists.

The National Association of City Transportation Officials recommends a range of 10 to 25 mph for most city streets, based on reducing crash risk for pedestrians and cyclists (NACTO, 2020). A recent report by the National Cooperative Highway Research Program has suggested a range of criteria, including the 50^th and 85^th percentile speeds, vehicle and bicycle traffic volumes, geometric considerations, traffic control devices and the presence of parking (National Academies of Sciences, Engineering, and Medicine, 2021). The report considers different road types, ranging from local roads to freeways, and different contexts, ranging from rural to urban core.

One problem with relying too much on the 85^th percentile speed to set limits it that it’s a moving target. 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  (Najjar et al., 2000; Retting & Cheung, 2008; Retting & Greene, 1997; Retting & Teoh, 2008). When speed limits are raised to meet the current 85th percentile speed, a new, higher 85th percentile speed usually results.

The establishment of the national maximum speed limit and its subsequent repeal provided ample opportunity to study the effects of lowering and raising speed limits.

Congress established the national maximum speed limit in 1973 in response to oil shortages. The U.S. Department of Transportation was directed 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 had 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.

Although the national maximum speed limit was imposed to conserve oil, its greatest effect was on safety. The National Research Council attributed 4,000 fewer fatalities to the decreased speeds in 1974 compared with 1973 (Transportation Research Board, 1984).

Not surprisingly, higher limits established after the 1995 repeal were associated with immediate increases in travel speeds. For example, 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%; the percent exceeding 75 mph increased from 4% to 17% (Retting & Greene, 1997). 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%.

As limits continued to rise to 70, 75 and 80 mph, travel speeds continued to go up (Hu, 2017; Retting & Teoh, 2008).

Fatalities also went up. Deaths on rural interstates increased 25%-30% when states began increasing speed limits from 55 to 65 mph in 1987 (Baum et al., 1989; Baum et al., 1990; Baum et al., 1991). In 1989, about two-thirds of this increase — 400 deaths — was attributed to increased speed and the rest to increased travel. 

An IIHS study examined longer-term changes. During 1993-2017, a 5 mph increase in the maximum state speed limit was associated with an 8% increase in fatality rates on interstates and freeways and a 3% increase on other roads (Farmer, 2019). In total, there were an estimated 37,000 more traffic fatalities during these years than would have been expected if maximum speed limits in 1993 had remained in place. In 2017 alone, there were more than 1,900 additional deaths.

The effect of speed limits on crashes and injuries isn’t limited to freeways.  An IIHS study found that the risk of crashes with fatal, serious or evident injuries in Seattle dropped between 11% and 20% on arterial roads when the city lowered its default speed limit from 30 mph to 25 mph on arterial roads (Hu & Cicchino, 2024).

Speed safety cameras, when used properly, can be an important tool for discouraging drivers from exceeding posted speed limits.

Most speed safety 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 safety cameras have been used to enforce speed limits in countries such as Australia and the United Kingdom.

Speed safety 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.

Speed safety cameras can substantially reduce speeding on a wide range of roads. IIHS 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%, respectively, six to eight months after cameras were introduced (Retting et al., 2008; Retting et al., 2008; Retting & Farmer, 2003).

An IIHS study in Montgomery County, Maryland, found that about 7½ years after the speed camera program began, the cameras were associated with a 10% reduction in mean speeds and a 62% 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 & McCartt, 2016).

A 2010 review published by the Cochrane Collaboration, an international public health organization, examined 35 studies from various countries. The authors concluded that speed safety cameras — including fixed, mobile, overt and covert devices — cut average speeds by 1%-15% and the percentage of vehicles traveling above the speed limits or designated speed thresholds by 14%-65% compared with sites without cameras (Wilson et al;. 2010).

Speed safety cameras have also been shown to reduce crashes and crash injuries. A 2009 study found that speed safety cameras could reduce injury crashes 47% on urban arterial roads (Shin et al., 2009). A study from Italy estimated that speed safety cameras could reduce fatal and injury crashes by 37% on urban expressways, freeways and principal arterials (Montella et al., 2014)

Speed safety cameras in Montgomery County were associated with an 8% reduction in the likelihood that a crash on a camera-eligible road was speeding-related and a 19% reduction in the likelihood that a crash involved an incapacitating or fatal injury (Hu & McCartt, 2016). A corridor approach, in which cameras were periodically moved along the length of a roadway segment, provided an additional 30% reduction in the likelihood that a crash involved an incapacitating or fatal injury over and above the effect of the cameras.

In its 2010 review, the Cochrane Collaboration summarized 28 studies that reported the effect on crashes and found reductions of 8%-49% for all crashes, 8%-50% for injury crashes and 11%-44% for crashes involving fatalities and serious injuries, in the vicinity of camera sites (Wilson et al., 2010). Over wider areas, the review found reductions of 9%-35% for all crashes, and 17%-58% for crashes involving fatalities and serious injuries. Reviewed studies with longer duration showed that these trends were either maintained or improved with time.

Speed safety cameras were in operation in 211 U.S. communities in 20 states and the District of Columbia during 2023, according to media sources and other public information tracked by IIHS, up from only four Arizona and Utah communities in 1995. Peoria, Arizona, and Paradise Valley, Arizona, were the first two communities to implement speed safety cameras in 1987. Cameras are currently used statewide in highway work zones in Arkansas, Connecticut, Illinois, Indiana, Maryland, New York, Oregon and Pennsylvania.

Trends in the number of U.S. communities with speed safety cameras

U.S. communities using speed safety cameras

Despite some vocal opposition, telephone surveys in jurisdictions with speed-camera programs show a majority of drivers support them.

A 2014 IIHS survey of 900 licensed drivers ages 18 and older residing in Montgomery County found that 62% of drivers favored automated speed enforcement on residential streets about 7½ years after camera ticketing began (Hu & McCartt, 2016).

A 2022 national survey of drivers ages 16 and older indicated that 43% supported the use of speed safety cameras to ticket drivers who travel more than 10 mph over the speed limit on residential streets (AAA Foundation for Traffic Safety, 2023).

A 2012 IIHS survey of 801 District of Columbia residents found strong support for speed safety cameras (Cicchino et al., 2014). D.C. has used speed cameras since 2001. In the survey, 88% 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% of residents who had not driven supported speed safety cameras.

In Scottsdale, Arizona, 63% of drivers surveyed prior to the start of automated enforcement said speed safety cameras should be used on an urban freeway where they were planned. After speed safety cameras were operational, 77% of drivers supported their use (Retting et al., 2008).

An automated enforcement program checklist published in 2021 by IIHS along with AAA, Advocates for Highway and Auto Safety, the Governors Highway Safety Association and the National Safety Council provides practical instructions for planning and implementing both red light camera and automated speed enforcement programs. The checklist aims to help communities follow best practices and maintain public support for the programs.

The U.S. Department of Transportation has its own guide, last updated in 2023, for planning and operating speed safety camera programs that improve safety and maintain reliability and accountability.

Traffic calming refers to roadway modifications, typically in urban and residential environments, that are intended to encourage slower speeds or reduce traffic volumes to improve livability and the safety of pedestrians and bicyclists. Traffic calming interventions often include changes in the geometry of the road so that the desired speed and traffic volume reductions are self-enforced.

A recent IIHS evaluation of the effects of a pilot speed management program in Bishopville, Maryland, found that a combination of traffic calming (specifically, lane narrowing), public outreach and enforcement resulted in substantial reductions in speeding (Hu & Cicchino, 2023).

Intelligent speed assistance (ISA), sometimes also called intelligent speed adaptation, 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 & Lind, 2002). A second approach is to introduce resistance to gas pedals, making it harder but still possible to speed (Varhelyi & Makinen, 2001). The most aggressive automated systems limit power so drivers can accelerate up to but not over the speed limit. These systems typically have an override option to allow drivers to temporarily surpass the top speed, such as when they want to pass. A fourth option is to give drivers incentives, such as auto insurance discounts, to slow down (Reagan et al., 2013).

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 & Lind, 2002).

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% to 83% (Reagan et al., 2013).

European researchers have found large reductions in speeding over periods ranging from months to over a year (Carsten, 2012).

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.

As of July 2024, all new vehicles sold in Europe are required to have standard ISA. Several manufacturers offer optional advisory ISA systems for vehicles sold in the U.S., and ISA systems that limit power are available as options on a limited number of vehicles. Manufacturers have begun to integrate camera-based speed limit recognition with cruise control to adjust the set speed based on the posted limit.

A recent IIHS survey found that more than 60% of U.S. drivers would accept a system that issued audible and visual warnings when they exceed the speed limit, and about half would accept a system that actively slowed the vehicle (Reagan & Cicchino, 2024).