October 2004

Speed: Highway Safety's Next Big Issue

The National Highway Traffic Safety Administration (NHTSA) lists speed as the third leading cause of fatalities and injuries in traffic crashes. Over the past several years, NHSTA concentrated significant resources on the two leading factors of traffic crashes - occupant protection and impaired driving. Little attention has been paid to speed, which caused the chair of GHSA to begin referring to the issue as "highway safety's neglected stepchild." In his remarks before the Lifesavers 22 Conference in March 2004, Jeff Runge, NHTSA Administrator, states "Speed continues to be cited as a major factor in almost one-third (32%) of traffic fatalities nationally and is estimated to cost $40 billion each year." State crash data for local roadways and collector roads also points to speed as a significant problem.

This is a trend that cannot be ignored.

Speed limit laws were first enacted in 1901 and have traditionally been the responsibility of states. The federal government controlled speed limits on the interstate highway system from 1973 until 1995, in an effort to decrease the nation's reliance on petroleum. In addition to complying with federal mandates, many states responded by reducing speeds on local roadways also. In 1995, the maximum speed limit law was repealed, allowing states to set their own limits on all roadways within each state's jurisdiction. (see www/ghsa.org for current information on speed limits in each state.)

Once federal controls were removed on the interstate system, many states also increased speed limits on local roadways, particularly on rural freeways. Not surprisingly, crash data since 1995 is showing continuing increases in the number of deaths attributed to speed.

In 1999, the Insurance Institute for Highway Safety funded a study of the effects of the repeal of the national maximum speed limit law. Researchers compared the number of motor vehicle deaths in 24 states that raised the speed limits with corresponding fatality counts in the 6 years prior to the repeal. Researchers also compared fatality counts from 7 states that didn't change speed limits. IIHS estimated a 15 percent increase in fatalities on interstates and freeways.

Today, despite the substantial social and technological changes that have occurred in the past decade, speed remains an important public policy and traffic safety issue.

Effects of Speed in Crashes

Speed limits are typically set based on roadway design. A curving two-lane rural road will have a different speed limit allowance than a modern controlled access freeway. Road characteristics that contribute to an assigned speed limit include sight distance (how far ahead the driver can see), road curvature, number of lanes, surface condition, the number of intersections, access to nearby commercial developments, whether the roadway is within city limits and so forth.

However, while road characteristics determine what is physically possible for a vehicle, adding the human element to the equation changes the outcome. Actual driving speed is strongly influenced by what seems appropriate to the driver at the time. The perception of risk, i.e. whether the driver perceives that he/she will be caught speeding, is also a factor in how well a posted speed limit is followed.

The relationship between vehicle speed and crash severity is based on the laws of physics. Excessive vehicle speed (speed above that for which the roadway was designed or speed too fast for conditions) has severe and often times disastrous effects in a crash, because speed:

    • Reduces a driver's ability to negotiate curves or maneuver around obstacles in the roadway
    • Extends the distance necessary for a vehicle to stop
    • Increases the distance a vehicle travels while the driver reacts to a hazard
    • Compromises the integrity of the vehicle structure
    • Decreases the effectiveness of vehicle design features such as airbags and restraint systems
    • Decreases the ability of roadway hardware such as guardrails, barriers and impact attenuators to protect occupants
    • Increases tread wear on tires and wear on braking systems
    • Increases the risk of crashes because other vehicles and pedestrians may not be able to judge distance accurately

In 1998, the Federal Highway Administration compiled a synthesis of safety research related to speed. Their findings are summarized as follows:

    • Crash risk is lowest near the average speed of traffic and increases for vehicles traveling much faster or slower than average.

    • When a crash occurs, its severity depends on the change in speed of the vehicle at impact. For example, severity is greater for a vehicle traveling at 70 mph at impact than for a vehicle traveling at 60 mph. This is particularly important in considering speed limits for trucks, because trucks require a much longer distance to stop.

    • In general, changing speed limits on low and moderate speed roads appears to have little or no effect on speed and crashes. This suggests that drivers travel at speeds they feel are reasonable and safe for the road and traffic, regardless of the posted speed limit.

    • On freeways and other high-speed roads, speed limit increases generally lead to higher speeds and crashes.

    • Most speed related crashes involve speed too fast for conditions.

    • Despite the large number of references concerning traffic calming devices (speed bumps, traffic circles, chevron striping, rumble strips and so forth) very few reports are available that contain a systematic evaluation. More research is needed to assess the system wide impacts and permit comparisons to be made on individual as well as combinations of traffic calming measures.

GHSA Urges Action

GHSA places a great deal of emphasis on the problem of speed. In early 2004, GHSA issued a call to action urging NHTSA to place greater emphasis on speeding and also conducted an informal survey of what states are doing to curb this problem. The results were aired in a news release earlier this year. To review the summary, click on www.ghsa.org. The Association urges NHTSA to endorse speed and red light camera programs, conduct more speed-related research and develop an anti-speeding communications strategy.

The NHTSA administrator should also use his bullypulpit to urge car companies to alter their advertising messages so they no longer glorify excessive speeding.

GHSA, the Insurance Institute for Highway Safety and NHTSA are in the preliminary stages of developing a national meeting to focus on the problem of excessive speeding. The goal is to examine existing research and recommend successful countermeasures.

To continue the Focus on Speed, the newly elected chair of GHSA listed speed at the top of his priorities his news release of October 19, 2004. Click here to view it...