The effects of the new 65 mile-per-hour speed limit on rural highway fatalities: A state-by-state analysis

doi:10.1016/0001-4575(90)90065-S

Accident Analysis & Prevention

Volume 22, Issue 2, April 1990, Pages 137-149

https://doi.org/10.1016/0001-4575(90)90065-S Get rights and content

Abstract

This paper examines the effects of the new 65 mile-per-hour (mph) speed limit on U.S. rural highway fatality counts. Separate analyses are conducted for each of the 40 states that had adopted the new (higher) limit by mid-1988. Using monthly Fatal Accident Reporting System (FARS) data from January 1976 through November 1988, time-series regression equations—including policy variables, seasonal variables, and surrogate exposure variables—are estimated for each state. The results suggest that the new laws have increased fatalities on both rural interstate and rural noninterstate highways in most states, but also that these effects differ substantially across the states. For rural interstate fatalities the estimates suggest a median (among the 40 states) effect of the increased speed limit of roughly 15% more fatalities; the median estimates for rural noninterstates suggest a 5% increase in fatalities due to the increased speed limits. Estimates such as those reported here should be revised as more information becomes available.

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Introduction: Speeding is considered to be a major contributor to road fatalities and injuries worldwide. Inappropriate speeding behavior is associated with a high casualty burden. It could be responsible for at least 30% of road accidents. Method: In 2018, the French authorities decided to introduce a new speed limit. They lowered the speed limit to 80 km/h on the unseparated interurban network. The aim was to reduce the number of fatalities and injuries and to implement some measures in line with international commitments. This paper uses different econometric models applied to time series for different groups of counties. Results: The results show a significant positive contribution of the new speed limit. The estimated number of lives saved is between 300 and 350. The overall reduction in the number of fatalities is 10%. The results also show a differentiated impact according to the local context and the different dynamics at play. Conclusions and Practical Applications: The results of this paper are in line with the scientific literature on speed limit reductions. They represent a validation of a debated public decision, while at the same time consolidating the body of knowledge on the subject, helping the decision-maker to adopt an appropriate measure to improve road safety performance.
Assessing the safety effectiveness of citywide speed limit reduction: A causal inference approach integrating propensity score matching and spatial difference-in-differences
2022, Transportation Research Part A: Policy and Practice
Citation Excerpt :
Early studies (Baum et al., 1989; Baum et al., 1990; Brown et al., 1990; Cetin et al., 2018; Engel, 1990; Engel and Thomsen, 1992; Farmer et al., 1999; Finch et al., 1994; Finch, 1994; Isaksson-Hellman and Töreki, 2019; Nilsson, 1990; Patterson et al., 2002; Persaud et al., 2010; Scharping, 1994; Webster and Layfield, 2003; Wood and Donnell, 2017) compared raw crash frequencies before and after speed limit changes without controlling for critical safety factors, which would result in biased estimates of the safety effectiveness. In addition, regression models such as time series models (Chang et al., 1993; Farmer et al., 1999; Gallaher et al., 1989; Garber and Graham, 1990; Grundy et al., 2009; Johansson, 1996; Ledolter and Chan, 1996; McKnight and Klein, 1990; Rock, 1995; Vernon et al., 2004; Wagenaar et al., 1990), cross-section regressions (Malyshkina and Mannering, 2008) and panel data models (Michener and Tighe, 1992; Ossiander and Cummings, 2002; Patterson et al., 2002) were also applied to estimate the safety effectiveness of speed limit changes by setting speed limit changes or speed limit as an independent variable after controlling for safety factors. Although the regression models can better capture the safety effectiveness of speed limit changes by controlling for safety factors, they are still subject to two critical issues: 1) time trend caused by unobserved factors, and 2) spatial spillover effect of treatment.
The New York City (NYC) initiated a new default speed limit law on November 7th, 2014, where speed limits on all road segments without a posted speed limit were reduced from 30 mph to 25 mph. The safety effectiveness of citywide speed limit reduction in an urban setting like NYC has been understudied in the literature. The high-density road network of NYC could lead to a significant spatial spillover effect of speed limit reduction on its neighboring sites. In addition, citywide speed limit reduction exerts much more treatment sites than control sites, which makes it challenging to identify sufficient control sites with similar covariates as the treated ones and thus may lead to confounding bias. Furthermore, there could also exist a time trend in crash observations caused by unobserved factors (e.g., enforcement, driving behaviors). To jointly account for spatial spillover effect, confounding bias, and time trend, this study proposes a novel causal inference approach integrating propensity score matching (PSM) and spatial difference-in-differences (SDID) to estimate the safety effectiveness of citywide speed limit reduction in NYC. The PSM utilizes a logistic generalized additive model (GAM) to capture the nonlinear relationship between covariates and the treatment indicator to reduce bias due to confounding variables. Moreover, the matched data are used to develop the SDID model that simultaneously captures spatial spillover effect and time trend via the extended difference-in-differences (DID) structure. The proposed causal approach suggests that the speed limit reduction would result in a 62.09% decrease in fatal crashes, with the spatial spillover effect found to be statistically significant. However, it does not indicate a significant change in injury and property-damage-only crashes as a result of the speed limit reduction. This study adds to the literature a robust causal inference approach for safety evaluation and provides researchers, practitioners, policy-makers insights into the safety effectiveness of the speed limit reduction in an urban setting.
The effect of speed reductions on collisions: A controlled before-and-after study in quebec, Canada
2021, Journal of Transport and Health
Speed limit reductions are known to decrease road risks where they are introduced since speed influences collision and injury severity. However, studies on the impact of speed limit reductions on collisions are limited since the 1990s, especially on roads that are not highways or freeways.
To evaluate the effect of speed limit reductions on collisions involving killed or seriously injured (KSI) persons in Quebec, Canada using a controlled before-and-after methodology where changes are not introduced all at once.
A database including all major provincial road segments (n = 3457) was built to reflect ad hoc speed changes introduced between 2006 and 2013 throughout the entire territory and on varying types of rural and periurban roads. The number of KSI three years prior and after speed limit changes were calculated for 20,437 segment-years with or without speed changes (control group). It was then used to model the effect of the speed reduction on segments with initial speeds of 70, 80 or 90 km/h and speed reductions of 10 or 20–40 km/h.
Using a zero inflated negative binomial and logistic regressions (at least 1 KSI vs. none), adjusting for decreasing KSI trends over time, traffic counts and segment length, we found a clear downward trend of KSI on all road segments, and a higher decrease where initial speed (90 km/h) were higher and speed reduction (20–40 km/h) were more important. Also, segments with sharp turns or with at least one intersection were more likely to have more KSI while divided two-lane roads were less likely to.
Our results add to the literature on the impact of speed reduction on major roads, helping provincial transportation managers to adopt evidence-based best practices.
How the speed limit policy affects travel speed?: Quasi-experimental approach
2021, Transport Policy
The objective of this study is to examine the effect of posted speed limit change on travel speeds. To do this, we use the National Performance Management Research Data Set (NPMRDS), which is a unique and rich dataset provided via the Federal Highway Administration (FHWA). Particularly, we focus on the impact of increased posted speed limit, implemented during June 2015, on interstate highways in Wisconsin including urban and rural areas between 2014 and 2016 by employing a quasi-experimental model with a panel dataset. Our findings clearly demonstrate that the posted speed limit change from 65 to 70 increases travel speed by 1.7 mph after controlling for location and time specific fixed-effects. Specifically, the posted speed limit change on Wisconsin interstate highways increases average travel speed of passenger and freight vehicles by 1.87 and 1.16 mph, respectively. Findings also show that speed variations have increased after the speed limit change, and higher variations do not occur in freight travel speeds, but in passenger vehicle travel speeds. These variations differently exist between urban and rural areas. We suggest that transportation agencies should consider these variations by vehicle types and places when they increase posted speed limit.
The complex relationship between increases to speed limits and traffic fatalities: Evidence from a meta-analysis
2019, Safety Science
Speed plays an important role in road safety as it affects accident risk and severity. Among safety policies implemented to control driving speed, speed limits are the most highly developed. Since the 1970′s, numerous studies have focused on the effectiveness of speed limits, but even today there is still no clear consensus as to the impact that raising the speed limit has on traffic fatalities. With the aim of consolidating knowledge on this topic, a meta-analysis has been carried out of a set of econometric studies assessing the effects on traffic fatalities of increasing speed limits in the US. Two sub-samples were obtained, taken from the traffic fatality measures considered by studies (fatality count and fatality rate normalized per vehicle miles traveled), and two approaches were analyzed: rural interstates (where speed limits were increased in 1987 and 1995), and a statewide approach (all roads network). Our findings show that by count traffic fatalities went up on both rural interstates and statewide level, although the effect was higher on rural interstates. In other respects, statewide fatality rates could be improved in relative terms by raising legal speed limits, although the effect would be weak.
Reliability-based user equilibrium in a transport network under the effects of speed limits and supply uncertainty
2018, Applied Mathematical Modelling
This study investigates the system-wide traffic flow re-allocation effect of speed limits in uncertain environments. Previous studies have only considered link capacity degradation, which is only one of the factors that lead to supply uncertainty. This study examines how imposing speed limits reallocates the traffic flows in a situation of general supply uncertainty with risk-averse travelers. The effects of imposing a link-specific speed limit on link driving speed and travel time are analyzed, given the link travel time distribution before imposing the speed limit. The expected travel time and travel time standard deviation of a link with a speed limit are derived from the link travel time distribution and are both continuous, monotone, and convex functions in terms of link flow. A distribution-free, reliability-based user equilibrium with speed limits is established, in which travelers are assumed to choose routes that minimize their own travel time budget. A variational inequality formulation for the equilibrium problem is proposed and the solution properties are provided. In this study, the inefficiency of a reliability-based user equilibrium flow pattern with speed limits is defined and found to be bounded above when supply uncertainty refers to capacity degradation. The upper bound depends on the level of risk aversion of travelers, a ratio related to the design and worst-case link capacities, and the highest power of all link performance functions.

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The effects of the new 65 mile-per-hour speed limit on rural highway fatalities: A state-by-state analysis

Abstract

J. Saf. Res.

Accid. Anal. Prev.

Economics Letters

Accid. Anal. Prev.

Accid. Anal. Prev.

J. Saf. Res.

Injury reduction and belt use associated with occupant restraint laws

Traffic safety and the business cycle

Alcohol, Drugs, and Driving

Risk Compensation and Safety Belt Use Laws