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

Abstract

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%). traffic speed, the rate of serious injury crashes to the third power, the rate of injury crashes to the second power, and the rate of property damage only crashes were proportionate to the first power of mean traffic speed [7]. According to this model, a 5% increase in mean traffic speed (e.g., from 100 to 105 kph), would result in a 22% increase in fatal crashes. Several meta-analyses found that Nilsson's "power model" is still a good fit for predicting the road trauma rate following speed limit changes on rural highways around the world [8][9][10].The relationship between speed and injury is complex [11]. Roads can be designed for safe, high speed travel by controlling access points, using barriers to separate opposing traffic and to prevent drivers from running off the road, providing adequate lane width and gradual curves, and including crash mitigation features [12][13][14][15]. Baruya analyzed speed and crash data from 139 European rural two lane highways and found a higher frequency of injury crashes in roads with more junctions (i.e., poorly controlled access) and/or narrower lanes, as well as roads with higher speed limits [16]. The role of road design is reflected in the risk of fatality after a crash on different types of high speed roads. French researchers found that crashes on rural highways were more than twice as likely to be fatal as crashes on high speed motorways. Motorways have median barriers to prevent head-on collisions and controlled access to prevent side impact (T-bone) collisions [17]. Crash mitigation features of the vehicle (e.g., airbags) or road (e.g., energy absorbing barriers) can also reduce injury severity following a collision. However, these measures are insufficient to prevent inj...

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