Raised Speed Limits Research Articles

Assessing the Safety Implications of Raising Speed Limits in Texas Freeways

Assessing the Safety Implications of Raising Speed Limits in Texas Freeways

How does an increased freeway speed limit influence the frequency of crashes on adjacent roads?

Urban arterial roads carry the most traffic on urban road networks and experience the highest percentage of crashes in urban areas. Safety on urban arterials that are adjacent to a higher speed freeway may be impacted by speed spillover or adaptation. The objective of this study was to determine the effects of raising freeway speed limits on the frequency of crashes on urban arterial roads adjacent to freeways (spillover effects). Crash data within Michigan were collected on 1393 urban arterial road segments before and after freeway speed limits were altered. Before-and-after data was collected simultaneously on 1470 comparison segments of urban arterial where speed limits did not change to control for the regression-to-the-mean bias. The mixed effects negative binomial (MENB) regression model was developed to analyze crash frequency on urban arterials. The results indicate that raising speed limits of freeways by as little as five miles per hour had a likelihood of increasing crash frequency on adjacent arterial roads by as much as 13.9 percent. To investigate if the safety impact of speed spillover changes with the distance from the freeway, influence areas (0–1 mile, 1–2 mile, and 2–3 mile) were used. The findings of this study provide insights into the effects of speed spillover on crash occurrences, and it demonstrates that increasing freeway speed limit has a negative influence on driver compliance with the speed limit on adjacent arterial roads. Correspondingly, the influence of freeway speed on drivers’ speeding behavior on adjacent urban arterials fades away with the distance from the freeway.

Road Safety Impact of Increased Rural Highway Speed Limits in British Columbia, Canada

Control of vehicle speed is a central tenet of the safe systems approach to road safety. Most research shows that raising speed limits results in more injuries. Advocates of higher speed limits argue that this conclusion is based on older research, that traffic fatalities are decreasing despite higher speed limits, and that modern vehicles are able to safely travel at higher speeds. These arguments were used to justify raising speed limits on rural highways in British Columbia, Canada (July 2014). We used an interrupted time series approach to evaluate the impact of these speed limit increases on fatal crashes, auto-insurance claims, and ambulance dispatches for road trauma. Events were mapped to affected road segments (with increased speed limits) and to nearby road segments (within 5 km of an affected segment). Separate linear regression models were fitted for each outcome and road segment group. Models included gasoline sales to account for changes in vehicle travel. Our main findings were significant increases in (i) total insurance claims (43.0%; 95% Confidence Interval [CI] = 16.0–76.4%), (ii) injury claims (30.0%; 95% CI = 9.5–54.2%), and (iii) fatal crashes (118.0; 95% CI = 10.9–225.1%) on affected road segments. Nearby segments had a 25.7% increase in insurance claims (95% CI = 16.1–36.1%).

How can the notion of optimal speed limits best be applied in urban areas?

This paper reviews estimates of optimal speed limits made in the past 30 years. A tendency is seen for optimal speed limits to become higher. In the most recent estimates made for Norway, the optimal speed limit was in no case lower than 60 km/h. Adopting a speed limit of 60 km/h on roads in urban areas now having speed limits of 30, 40 or 50 km/h would most likely lead to an increase in the number of accidents and killed or injured road users. It is a political objective in Norway to reduce the number of killed or injured road users and to encourage more walking and cycling. Raising speed limits would conflict with both these objectives. This paper discusses if a re-interpretation of the notion of optimal speed limits can applied to justify low speed limits in urban areas. Traditionally, analyses of optimal speed limits have included motorised travel only. It is shown by means of simple numerical examples, that by including the effects of motorised travel speed on walking and cycling, optimal speed limits tend to be lower than when only motorised travel is included.

Effects of higher maximum speed limits to vehicle speeds: A before - after analysis on rural divided highways in Vietnam

This study is to assess the effects of raising speed limits to vehicle operating speeds on rural divided highways in Vietnam. Vehicle speeds were recorded at three different sites of three routes during the daytime and nighttime, both before and after speed limits on these sites increasing from 80 km/h to 90 km/h. The results have shown that the percentage of speeds exceeding speed limits had a wide range from 0% to nearly 30% with regard to different locations, survey time and speed limits. The extent of speeding in some cases was very high even after speed limit increased. It was found that in most cases, the changes in mean speeds after a higher speed limit was applied were statistically significant at the p-value of 0.05, however, the magnitudes of the mean change varied considerably between locations and survey times. Because four out of six cases under the study having mean speeds increased by over 10 km/h after setting up a higher speed limit, this study suggests that further appropriate measures of speed control and speed management should be applied along with increasing speed limit to ensure traffic safety on rural divided highways in Vietnam.
 Article history: Received 27 March 2018, Revised 18 April 2018, Accepted 27 April 2018

What is the optimal speed limit on freeways?

When choosing his speed, a driver faces a trade-off between private benefits (time savings) and private costs (fuel cost and own damage and injury). Driving faster also has external costs (pollution, adverse health impacts and injury to other drivers). This paper uses large-scale speed limit increases in the western United States in 1987 and 1996 to address three related questions. First, do the social benefits of raising speed limits exceed the social costs? Second, do the private benefits of driving faster exceed the private costs? Third, what is the optimal speed limit? I find that a 10mph speed limit increase on highways leads to a 3–4mph increase in travel speed, 9–15% more accidents, 34–60% more fatal accidents, and elevated pollutant concentrations of 14–24% (carbon monoxide), 8–15% (nitrogen oxides), 1–11% (ozone) and 9% higher fetal death rates around the affected freeways. Using these estimates, I find that the social costs of speed limit increases are two to seven times larger than the social benefits. In contrast, many individual drivers would enjoy a net private benefit from driving faster. Privately, a value of a statistical life (VSL) of $6.0 million or less justifies driving faster, but the social planner's VSL could be at most $0.9–$2.0 million to justify higher speed limits. I conclude that the optimal speed limit was lower, but not much lower, than 55mph.

Commentary: Driver Monitoring and Feedback: Not Just “I Told You So”

Commentary: Driver Monitoring and Feedback: Not Just “I Told You So”

Long-Term Effects of Repealing the National Maximum Speed Limit in the United States

We examined the long-term effects of the 1995 repeal of federal speed limit controls on road fatalities and injuries in fatal crashes. We used a Poisson mixed-regression model to assess changes in the number of fatalities and injuries in fatal crashes between 1995 and 2005 on rural interstates, where all US states have raised speed limits since the repeal, as well as on urban interstates and noninterstate roads, where many states have raised speed limits. We found a 3.2% increase in road fatalities attributable to the raised speed limits on all road types in the United States. The highest increases were on rural interstates (9.1%) and urban interstates (4.0%). We estimated that 12 545 deaths (95% confidence interval [CI] = 8739, 16 352) and 36 583 injuries in fatal crashes (95% CI = 29 322, 43 844) were attributable to increases in speed limits across the United States. Reduced speed limits and improved enforcement with speed camera networks could immediately reduce speeds and save lives, in addition to reducing gas consumption, cutting emissions of air pollutants, saving valuable years of productivity, and reducing the cost of motor vehicle crashes.

Raised speed limits, case fatality and road deaths: a six year follow-up using ARIMA models

Background: In November 1993, the Israeli government increased the speed limit for all vehicles from 90 to 100 km per hour on a total of 115 km of its three...

SPEED, ROAD INJURY, AND PUBLIC HEALTH

We review milestones in the history of increases in speed limits and travel speeds ("speed creep") and risks for road deaths and injury. Reduced speed limits, speed-camera networks, and speed calming substantially reduce these tolls in absolute numbers-a trend that is apparent in the United Kingdom, Australia, France, and other countries, but not in the United States, which has raised speed limits and does not have speed-camera networks. Newtonian relationships between the fourth power of small increases or reductions in speed and large increases or reductions in deaths state the case for speed control. Speed adaptation and the interaction between speed and other determinants of injury risks, including congestion and countermeasures, enter into these relationships. Speed-camera networks and speed calming lead to large, sustainable, and highly cost-effective drops in road deaths and injuries and should target entire populations, not merely high-risk subgroups or situations. Yet, there are major barriers to preventive strategies based on the discovery that speed kills. Modal shifts from speed on roads to speed on rail, lower maximum vehicle speeds, and speed-camera networks are required for progress toward Vision Zero-the goal of no road deaths-through Killing Speed. The human cost of the delay in killing speed in the United States may be as high as 20,000 lives lost per year.

Death and Injury from Motor Vehicle Crashes: A Tale of Two Countries

To determine why road deaths dropped by 33.9% in the United Kingdom, compared to 6.5% in the United States, between 1990 and 1999. Deaths per billion vehicle kilometers traveled (D/BVKM), and case fatality rates (CFR) in the United States and the United Kingdom were tracked. Time trends in CFR can be used to track the direct effects of speed of impact. CFR is a crash-phase outcome that is independent of exposure, and varies approximately to the fourth power of the speed of crash impact. Joinpoint regression analysis was used to analyze changes in time trends of CFR. In the 1990s, the decrease in deaths in the United Kingdom was attributable mostly to the 29.6% drop in the CFR. In the United States, the CFR dropped by only 6.6%. The United Kingdom introduced speed cameras and an array of speed-calming measures. By contrast, in the United States, use of speed cameras was extremely rare, and speed limits and speeds increased in 32 of the 50 states, mostly in 1995 and 1996, after which CFR actually rose (p<.0001). Intercountry differences in time trends in seat belt use, trauma care, vehicle kilometers traveled, congestion, and driving under the influence of alcohol (DUI), along with massive increase in use of higher-risk sports utility vehicles in the United States, did not account for the contrasting trends in deaths through the 1990s. But increases in DUI in the United States after 1997 may have contributed to increases in speed-related crashes. The reductions in CFR, probably from small drops in speed of impact account for the disproportionately greater drop in death tolls in the United Kingdom compared to the United States. The temporal fit between drops in CFR and deaths following the introduction of speed cameras in the United Kingdom and increases in speed (speed creep), CFR, and deaths in the United States following raised speed limits suggests that diverging changes in speeds of impact accounted mainly for these changes. Use of D/BVKM to correct for exposure concealed the lack of progress after 1990 in the United States, since falling time trends in D/BVKM reflect increases in congestion. If the United States had implemented United Kingdom-type speed control policies and not raised speed limits, there would have been an estimated 6500 to 10,000 (approximately 16% to 25%) fewer road deaths per year during the period following speed-limit increases (1996 to 1999), including many DUI-related deaths. Reductions of up to 50% are now achievable based on newer population-wide strategies for speed control.

Raised speed limits, speed spillover, case-fatality rates, and road deaths in Israel: a 5-year follow-up.

We assessed the 5-year, nationwide impact on road deaths of the raise in the speed limit (November 1, 1993) on 3 major interurban highways in Israel from 90 to 100 kph. We compared before-after trends in deaths as well as case fatality-an outcome independent of exposure (defined as vehicle-kilometers traveled). After the raise, speeds rose by 4.5%-9.1%. Over 5 years, there was a sustained increase in deaths (15%) and case fatality rates (38%) on all interurban roads. Corresponding increases in deaths (13%) and case fatality (24%) on urban roads indicated "speed spillover." Immediate increases in case fatality predicted and tracked the sustained increase in deaths from increased speeds of impact. Newtonian fourth power models predicted the effects of "small" increases in speed on large rises in case fatality rates. Countermeasures and congestion reduced the impact on deaths and case-fatality rates by more than half.

Changes in motor vehicle occupant fatalities after repeal of the national maximum speed limit

Trends in motor vehicle occupant deaths over 8 years were studied for 24 states that raised interstate speed limits and seven states that did not following the 1995 repeal of the US National Maximum Speed Limit. Fatalities on interstates increased 15% in the 24 states that raised speed limits. After accounting for changes in vehicle miles of travel, fatality rates were 17% higher following the speed limit increases. Similar increases were reported following the 1987 speed limit increases on rural interstates. Deaths on roads other than interstates were essentially unchanged.

An Empirical Analysis of the Direct and Indirect Effects of Relaxed Interstate Speed Limits on Highway Safety

In April 1987, the federal government enacted the Federal Highway Bill which, among its other provisions, permitted states to increase speed limits on rural sections of their interstate highways. Forty states have responded to the enabling legislation by raising their speed limits which has fueled an ongoing debate regarding the highway safety effects of higher speed limits. Contributing to the discussion, this paper reports the results of annual cross-section–time series analyses of highway safety in California, which raised speed limits in May 1987. Based upon a 9-year sample from 1981 to 1989, the higher speed limits are found to have no system-wide effects on total, fatal, injury-related, or property damage accidents. Redistribution effects, however, were identified in that counties with 65 mph highways experienced a significant increase in each accident category.