New moves toward predictive approaches to traffic safety

For all the resources focused on high-crash hotspots (specific areas host to a higher-than-average number of crashes), in Minnesota, for one, there aren’t many. Expert and engineer Howard Preston, who has worked in traffic safety for 40 years, explains to blog Next City his real safety concerns: targeting scattered crashes. “Severe crashes are scattered around the system,” he says, “but they’re not randomly scattered.”

To spend resources scouring roads for traffic crash hotspots is to miss the point – traffic accidents are spread throughout road systems, according to one traffic safety expert. From Jonathan Kos-Read.

Preston, like other experts, has devoted time to analyzing hotspots and dead man’s curves, those “roads or intersections that were conspicuously dangerous, leading to a steady stream of accidents and tragedies.” Yet, when he and other engineers were unable to pinpoint them, money was removed from certain areas’ traffic safety programs “because they couldn’t find any high-crash locations.”

Funding for such safety programs is very much needed, but requires a specific approach: understanding how crashes are scattered throughout the system. Preston and his associates created “a new science,” analyzing the areas where serious crashes took place, and then figuring out which other areas have similar features. The approach is more predictive than reactive. As Next City notes, it’s “part of a broader trend in pedestrian safety planning that seeks to be more proactive — to identify and mitigate risks before they lead to collisions.”

In one case, Preston analyzed the Minneapolis/St. Paul metropolitan area, discovering that over a recent five-year timeframe, all of the severe pedestrian and bike crashes took place at 130 — or six percent — of the area’s 2,215 intersections. However, the majority of these pinpointed areas had a single severe crash. None of the areas had more than a few. Preston found that, in this case, there were no hotspots.

Yet Preston also discovered that the crash areas shared several features: “multi-lane and undivided roads, with high traffic volume (more than 17,500 vehicles per day), and other environmental characteristics, such as bus stops and ‘pedestrian generators’ (for example, stores and restaurants).” Preston then classified about 700 more intersections which shared at minimum four of those characteristics, and suggested these receive safety upgrades.

The approach, which Preston calls “systemic,” is more effective than the traditional method, argues Preston. “The reactive approach would not have identified enough locations for improvements.” It “finds a middle ground between universal upgrades and focusing only on the places where crashes have already occurred,” notes Next City. So far, New Jersey, North Dakota, and Missouri have started implementing the approach, as shared by Preston in these guidelines.

The triage mentality, which doesn’t address root causes of crashes but rather the end result, is common, often because of financial pressures. As David Goldberg, who co-authored a recent Smart Growth America report on pedestrian fatalities, explains to Next City, cities have frequently chosen “the band-aid approach; you look for where the sore erupts and you put a band-aid on it. But if there’s an underlying disease or skin condition that’s causing the sores, you sort of don’t get at that.”

Other predictive approaches to traffic safety have been developed, including the 2008 National Cooperative Highway Research Program’s Pedestrian Safety Prediction Methodology, which relies on data from Toronto and Charlotte, and an in-progress program from San Francisco’s Department of Public Health, customized for that city.

Even as predictive approaches gain traction, hot spot analysis remains significant, especially in particularly dangerous areas with histories of frequent crashes. As one expert, Anne Moudon, who ran a study of high-injury areas in the Seattle area, argues, “The first thing to do is reduce the collisions in hot spots. It’s a big problem, so don’t look for where else can the problem occur, look for resolving the problem where it is.”

Tags: Jonathan Kos-Read, Minnesota, New Jersey, North Dakota, Preston, Road traffic safety, Smart Growth America, Traffic collision

Category: Automotive, Road safety