Speed Limit Increase Research Articles

Temporal, Spatial, and Landscape Habitat Characteristics of Moose—Vehicle Collisions in Western Maine

Abstract:We analyzed moose (Alces alces)‐vehicle collisions (MVCs) in western Maine, USA, from 1992 to 2005 (n= 8,156) using Geographic Information Systems to identify patterns of temporal and spatial distribution and develop predictive models based on road and landscape characteristics. We used chi‐square and correlation analyses to assess temporal characteristics of MVCs,K‐function and kernel analyses to identify spatial clusters of MVCs, and logistic regression to relate covariates for traffic, land‐cover, land‐form, and relative moose abundance to probability of MVC. We evaluated candidate models using Akaike's Information Criterion, area under the receiver operating characteristic curve (AUC), and the percentage of correctly classified observations. Most (81.6%) MVCs occurred from May to October, with peak monthly frequencies in June (18.6%). Moose‐vehicle collisions were clustered spatially on roads at local (0–4 km) and regional scales (22–41 km and 45–54 km), but not at intermediate scales. Traffic‐related covariates predicting MVCs included traffic volume and speed limit. For each additional 500 vehicles/day, odds of a location being an MVC increased by 57%. For each 8‐km/hr increase in speed limit, odds of an MVC increased by 35%. Landscape composition covariates best predicted MVCs within a 2.5‐km radius of the collision site. Mean percent cover within 2.5 km of MVCs was comprised of 36% more cutover forest, 10% more coniferous forest, 5% less deciduous‐mixed forest, and 10% less nonwoody wetland than for random points. For every 5% increase in percent cutover and coniferous forest within 2.5 km of the road, predicted odds of MVC increased by 36% and 19%, respectively. Landscape configuration covariates best predicted MVCs within the 5.0‐km radius. Moose‐vehicle collisions were associated with areas of less interspersion of cover types; for each 5% increase in an index of interspersion‐juxtaposition, predicted odds of MVC decreased by 11%. Our final model attained high predictive power (AUC = 0.835) and validation accuracy (75.0%). The model also proved robust to physiographic variation, exhibiting high predictive power (AUC = 0.828) and validation accuracy (68.8%). Managers seeking to prioritize resources for reducing MVCs or predicting future areas of high MVC probability should assess land‐cover composition and configuration surrounding MVC hotspots at geographic extents out to 2.5–5 km and use this information to plan expensive roadside management practices such as fencing. The importance of traffic and landscape covariates in our modeling suggests that effective management to reduce MVCs will require a complex combination of driving speed reductions and modifications to forest management along roads.

Hacia unos límites de velocidad más consistentes

This article includes a brief description and justification of the proposal presented to the Spanish Parliament by the author (*) at the request of the Spanish Commission on Road Safety. It describes the basic principles upon which the association between road speed limits and real road records should be considered. Therefore, road sections with high accidentality rates should be ‘penalized’ with the reduction of generic speed limits, depending on the type of roads, whilst low-accidentality-rates road sections could be positively awarded by increasing speed limits. The aim is to achieve more reasonable, credible and widely accepted signalling criteria according to drivers expectation.

Traffic speeds associated with implementation of 80 mph speed limits on West Texas rural interstates

Problem In 2006 Texas raised the daytime speed limit for passenger vehicles on segments of I-10 and I-20 from 75 to 80 mph. Methods: Traffic speeds were measured before and 3, 12, and 16 months after the limit was changed. Results: 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. Limiting the analysis to the month before the speed limit change and 1 year later, the proportion of drivers exceeding 80 mph was 18 times higher on I-20 and 2 times higher on I-10. Discussion: The smaller speed increases on I-10 may be related to its proximity to the U.S. border with Mexico. Highly visible border patrol activity coincided with posting of the higher speed limit. Long-term monitoring in other states suggests that traffic speeds in Texas are likely to continue to increase. Impact on Industry: The present study adds to the wealth of evidence that increased speed limits lead to increased travel speeds. The primary countermeasures to reduce the risk of speed-related crashes include highly visible police traffic enforcement and the use of speed cameras accompanied by publicity.

Integrating Accident and Travel Delay Externalities in an Urban Speed Reduction Context

Accident externality costs remain controversial in terms of their costing and valuation. Much of the literature on accident and travel delay externalities treats each source as mutually exclusive and additive, yet common sense suggests that interdependencies prevail. One example of this is the recognition that accident externalities are not independent of travel delays, and hence travel time savings and losses are influenced by policy designed to reduce the risk of exposure to accidents. Reduced maximum speed limit restrictions also add costs in terms of loss of travel time (and increased speed limits produce travel time benefits). Also, lowered speed limits may lead to more drivers risking exceeding the speed limit because of perceived time loss, thereby exacerbating the potential for accidents. The paper takes a close look at the empirical relationship between accident and travel delay externalities in an urban setting, accounting for the risk‐compensating behaviour under conditions of greater accident risk. Recognizing that levels of risk in an urban setting are broadly a function of traffic densities and that the latter can be approximated by the mix of free flow and non‐free flow travel time (for a given total travel time), an aggregate marginal externality cost function is used to quantify empirically the input elements in the context of a driver’s choice between a free and a tolled route in Sydney, Australia. This discrete choice context is sufficient, given an externally established relationship between speed and traffic density, to quantify the marginal externality accident and travel time delay costs. It is shown what additional externality has to be factored into the accident costs to recognize the other sources of externality typically ignored in accident costing and speed restriction studies.

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.

Evaluation of variable speed limits for real-time freeway safety improvement

Use of various variable speed limit (VSL) strategies as a tool for safety improvement on freeways was evaluated using simulation of a section of Interstate 4 in Orlando, FL. Real-time crash likelihood was calculated based on models developed in previous research by the first author [Abdel-Aty, M., Uddin, N., Pande, A., January 2005. Split models for predicting multi-vehicle crashes during high-speed and low-speed operating conditions on freeways. In: Presented at the 84th Annual Meeting of the Transportation Research Board, Washington, DC]. VSL implementation produced safety improvement by simultaneously implementing lower speed limits upstream and higher speed limits downstream of the location where crash likelihood is observed in real-time. This improvement was realized in the case of medium-to-high-speed regimes on the freeway, but no benefit was achieved in low-speed situations (no substantial safety benefit from implementing VSL in congested situation's simulation). The final recommendations for implementing VSL are: • gradually introducing speed limit changes over time (5 mph every 10 min); • abruptly changing speed limit in space (no gap distance); • reducing speed limits upstream and increasing speed limits downstream of location of interest; • the speed limit changes up- and downstream should be large in magnitude (15 mph) and implemented within short distances (2 miles) of the location of interest. In addition to the safety benefit, this final strategy also produced travel time savings.

Estimating the Value of a Statistical Life: The Importance of Omitted Variables and Publication Bias

Measures of public preferences toward risk are critical to evaluations of public policies on many safety, environmental, and health issues. In this paper we provide a method for measuring the revealed preferences for safety risks from state level public choices about speed limits. The idea is to measure the value of the time saved per incremental fatality that results from the voluntary adoption of an increased speed limit. Since adopters must have valued the time saved by greater speeds more than the fatalities created, this ratio provides a convincing and credible upper bound on the value of a statistical life (VSL).

70-mph speed limit and motor vehicular fatalities on interstate highways.

In May 1996, Alabama increased the rural interstate highways speed limit to 70 mph. This study was conducted to determine if the faster speed limit had any influence on the number of motor vehicular crash (MVC) deaths. The null hypothesis was that no significant change occurred in the number of deaths since the faster speed was introduced. Using MVC fatality data collected by the Alabama Department of Public Safety and published by the state of Alabama from 1984 to 1999, a time-series study designed was used to examine the number of MVC deaths before and after the speed limit change. The trend of MVC deaths was examined for both rural and urban interstate highways and those occurring on Federal and state highways. There were 174 interstate MVC deaths in 1997 and 165 in 1999; both figures represent a significant increase (P <.05) from the trend of previous years' results. State and Federal highways demonstrated no significant change. By 1998 the number of interstate highway MVC deaths dropped to 114, falling back within the expected trend established by the results of the previous years. The number of rural interstate MVC deaths was found to be significant in 1997 and 1999. The faster speed limit was associated with an increase in MVC deaths for the first year after the speed limit increase. The decline in the number of MVC deaths for 1998 was unanticipated. There are many other factors that need to be evaluated before determining the cause and effect that higher speed limits have on MVC fatalities.

The fatality effects of highway speed limits by gender and age

This study presents panel-based evidence on the overall fatality consequences of recent speed-limit increases in the United States. The results suggest that higher speed limits had highly heterogeneous effects, generally increasing fatalities among women and the elderly but reducing them among males.

Effect of repeal of the national maximum speed limit law on occurrence of crashes, injury crashes, and fatal crashes on Utah highways

Speed limits were increased in Utah and other States after repeal of the national maximum speed limit law (NMSL) in 1995. This study analyzed effects of the increased speed limit on Utah highways on crash rates, fatality crash rates, and injury crash rates. Annual (1992–1999) rates of crashes, fatality crashes, and injury crashes for the following highway categories were calculated: urban Interstate segments (current speed limit 60–65 miles per hour (mph)); rural Interstate segments (current speed limit 70–75 mph); 55 mph rural non-Interstate highway segments; and high-speed non-Interstate highways (current speed limit 60–65 mph). Data were analyzed using autoregressive integrative moving average intervention time series analysis techniques. There were significant increases in total crash rates on urban (60–65 mph) Interstate segments (confounded by extensive ongoing highway construction on these highways), and in fatal crash rates on high-speed (60–65 mph) rural non-Interstate segments. The following variables were unaffected: total, fatality, and injury crash rates on rural Interstate segments; fatality and injury crash rates on urban Interstate segments; total and injury crash rates on high-speed non-Interstate segments. These results show an adverse effect on crash occurrence for subsets of crash types and highways, but do not show a major overall effect of NMSL repeal and increased speed limit on crash occurrence on Utah highways.

Are SUVs “Supremely Unsafe Vehicles”?: Analysis of Rollovers and Injuries with Sport Utility Vehicles

With increasing speed limits and more light trucks penetrating the market, concern over their rollover risk is growing. In particular, the general public and automobile manufacturers would like to know if the increasingly popular sport utility vehicles (SUVs) are indeed safer than other vehicle platforms. The influences of various vehicle platforms on rollovers and driver injuries were investigated. Specifically, ( a) the rollover intensities of SUVs vis-à-vis those of other vehicle types in single-vehicle crashes and ( b) the severity of the resulting driver injury were explored. Data from a good-quality federally maintained database were used for crash analysis. The database contains a relatively clean stratified sample of police-reported tow-away crashes nationwide, and it contains detailed information about vehicle rollovers. Rollover intensity, captured by the number of quarter turns, was investigated by using weighted negative binomial models; injury severity, measured on the abbreviated injury scale, was examined by using weighted ordered logit models. New insights emerged about the factors that increase rollover intensity and injury severity. As expected, SUVs are more likely to roll over and therefore injure their occupant drivers more severely. However, SUVs also protect their drivers during collisions because of their greater crashworthiness. In fact, the SUV crashworthiness effect exceeds the rollover effect, on average. The implications of these findings are discussed.

A model of traffic crashes in New Zealand

The aim of this study was to examine the changes in the trend and seasonal patterns in fatal crashes in New Zealand in relation to changes in economic conditions between 1970 and 1994. The Harvey and Durbin (Journal of the Royal Statistical Society 149 (3) (1986) 187–227) structural time series model (STSM), an ‘unobserved components’ class of model, was used to estimate models for quarterly fatal traffic crashes. The dependent variable was modelled as the number of crashes and three variants of the crash rate (crashes per 10,000 km travelled, crashes per 1,000 vehicles, and crashes per 1000 population). Independent variables included in the models were unemployment rate (UER), real gross domestic product per capita, the proportion of motorcycles, the proportion of young males in the population, alcohol consumption per capita, the open road speed limit, and dummy variables for the 1973 and 1979 oil crises and seat belt wearing laws. UERs, real GDP per capita, and alcohol consumption were all significant and important factors in explaining the short-run dynamics of the models. In the long-run, real GDP per capita was directly related to the number of crashes but after controlling for distance travelled was not significant. This suggests increases in income are associated with a short-run reduction in risk but increases in exposure to a crash (i.e. distance travelled) in the long-run. A 1% increase in the open road speed limit was associated with a long-run 0.5% increase in fatal crashes. Substantial reductions in fatal crashes were associated with the 1979 oil crisis and seat belt wearing laws. The 1984 universal seat belt wearing law was associated with a sustained 15.6% reduction in fatal crashes. These road policy factors appeared to have a greater influence on crashes than the role of demographic and economic factors.

Freeway speed limits and traffic fatalities in Washington State

Background: In 1987 individual states in the USA were allowed to raise speed limits on rural freeways from 55 to 65 mph. Analyses of the impact of the increased speed limits on highway safety have produced conflicting results. Objective: To determine if the 1987 speed limit increase on Washington State's rural freeways affected the incidence of fatal crashes or all crashes on rural freeways, or affected average vehicle speeds or speed variance. Design: An ecological study of crashes and vehicle speeds on Washington State freeways from 1974 through 1994. Results: The incidence of fatal crashes more than doubled after 1987, compared with what would have been expected if there had been no speed limit increase, rate ratio 2.1 (95% confidence interval (CI), 1.6–2.7). This resulted in an excess of 26.4 deaths per year on rural freeways in Washington State. The total crash rate did not change substantially, rate ratio 1.1 (95% CI, 1.0–1.3). Average vehicle speed increased by 5.5 mph. Speed variance was not affected by the speed limit increase. Conclusions: The speed limit increase was associated with a higher fatal crash rate and more deaths on freeways in Washington State.

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.

Effect of Speed Limit Increases on Crash Injury Severity: Analysis of Single-Vehicle Crashes on North Carolina Interstate Highways

The recent congressional action revoking the national maximum speed limits has rekindled the debate over safety and travel time tradeoff. The effect of speed limit increases on the most severe occupant injury in a crash is analyzed here. Single-vehicle crashes on Interstate highways in North Carolina ( N = 2729) are examined. Two analysis methods are used: a paired-comparison analysis and an ordered probit model. Increasing speed limits from 88.5 to 96.6 km/h (55 to 60 mph) and from 88.5 to 104.6 km/h (55 to 65 mph) increased the probability of sustaining minor and nonincapacitating injuries, but increasing speed limits from 104.6 to 112.7 km/h (65 to 70 mph) did not have a significant effect on crash severity. There were too few fatal crashes to draw conclusive results for this category of injury severity. Crashes involving the face of a guardrail were more severe on segments where the speed limit was raised than on comparison segments or study segments before the limits were increased. These findings may be conservative because study segments with good safety records were chosen for the speed limit increases.

Experimental Study on Static and Dynamic Characteristics of Annular Plain Seals With Porous Materials

Static and dynamic characteristics are experimentally investigated for annular plain seals with porous materials applied to the seal surface by insertion into the middle of the seal. Experimental results show that annular plain seals with porous materials have a higher leakage flow rate, larger main stiffness coefficients, and smaller cross-coupled stiffness coefficients and main damping coefficients than conventional annular plain seals with solid surfaces. In the porous seals, an increase of approximately 30 percent in the leakage flow rate and reduction of the same amount in the main damping coefficients are obtained, whereas the main stiffness coefficients for the porous seals are four to six times as much as those for the solid seals due to the increase in the hydrostatic force induced by a function of the hydrostatic porous bearing. This suggests that the quantitative effects of the porous materials on the main stiffness coefficients are much more significant than the effects on the leakage flow rate and the other dynamic coefficients. The larger main stiffness coefficients for the porous seals yield larger radial reaction force for a small concentric whirling motion, which would contribute to rotor stability from the viewpoint of increasing speed limits due to a stiffer rotor support.

Impact of 65-mph Speed Limit on Iowa’s Rural Interstate Highways: Integrated Bayesian Forecasting and Dynamic Modeling Approach

In 1987, a provision of the Surface Transportation and Uniform Relocation Assistance Act allowed states to raise speed limits on rural Interstates to 65 mph (104.6 km/h). By 1995, nearly all states had done so. Several studies have investigated the safety impacts of these increases. Methodologies varied from analysis of variance to simple before and after comparison and have included time series procedures, with and without intervention variables. In general, these studies have produced contradictory findings. An integrated Bayesian forecasting and dynamic modeling approach used to determine the impact of the increased speed limit on rural Interstates of Iowa is reported. The approach is used to verify that raising the speed limit to 65 mph (104.6 km/h) led to an increase in fatal accidents on rural Interstates of Iowa. Comparison of fatal accident data on rural Interstates of Iowa and New Jersey yields similar results. Although this conclusion was anticipated, the study further demonstrates that a Bayesian/dynamic approach is more robust than the standard time series model.

RESOURCE ALLOCATION IN PUBLIC POLICY: THE EFFECTS OF THE 65‐MPH SPEED LIMIT

In 1987 the U.S. government allowed states to raise speed limits to 65‐mph on some highways. We evaluate the consequences using a resource allocation perspective: the chance to drive faster reallocates traffic from side roads to the safer interstate highways, and a higher speed limit permits highway patrols to shift manpower from speed enforcement to other safety activities. This perspective implies that we should measure the effect of a speed limit by its systemwide rather than its local effects. We do so and find that the fatality rate dropped by 3.49%‐5.1% following the speed limit increase. (JEL A10, R40)

EPA Watch: Increased speed limits will not trigger changes to SIPs

EPA Watch: Increased speed limits will not trigger changes to SIPs

A driving-simulator test of Wilde's risk homeostasis theory.

Previous experimental tests of risk homeostasis theory (RHT) have failed to manipulate both motivational and nonmotivational variables in an ecologivally valid within-subjects design. In this study, 24 Ss operated an interactive driving simulator under varying levels of a within-subject motivational factor (monetary accident cost), a within-subject nonmotivational factor (speed limit), and a between-subjects nonmotivational factor (speeding fine). Consistent with RHT, increased speed limit and reduced speeding fine significantly increased driving speed but had no effect on accident frequency. Moreover, increased accident cost caused large and significant reductions in accident frequency but no change in speed choice