IIHS Study Says Low-Cost Alterations Can Reduce Urban Road Crashes

Spending a small amount of money on busy roadways in cities can reduce the number of automobile crashes, according to a recent study from the Insurance Institute for Highway Safety.

The Institute’s findings follow a recently released government report that said traffic deaths dropped on U.S. highways for a second straight year, with 42,636 fatalities in 2004, a reduction of more than 200 from 2003. The fatality rate on the nation’s highways in 2004 was the lowest since record-keeping began 30 years ago, according to the U.S. Department of Transportation’s National High-way Traffic Safety Administration (NHTSA). The NHTSA has estimated highway crashes cost society $230.6 billion a year, about $820 per person.

While the majority of crash deaths occur on rural roads, motorists drive two billion miles every day on urban arterial roads. About 8,000 deaths and more than one million injuries take place each year on these roads.

According to Richard Retting, senior transportation engineer at the IIHS, “Urban arterials weren’t built to accommodate today’s heavy traffic. They’ve evolved as traffic has increased, and they haven’t always evolved in the best way to enhance safety and ensure a smooth flow of traffic. So it’s a matter of studying urban arterials to pinpoint where crashes are occurring frequently and then identifying potential solutions, looking first for less costly measures that can be implemented more quickly than major re-engineering.”

To show how to decrease crashes by applying less costly and complex measures, Retting spearheaded a project involving a major arterial in suburban Fairfax County, Va., near Washington, D.C.

The researchers analyzed traffic on Leesburg Pike, noted problems that were causing crashes, and then suggested measures such as protected left-turn signals at problem intersections or moving a bus stop a few hundred feet. At a pair of the six locations where such measures were applied, crash types that had been overrepresented were reduced to zero. At four other intersections, the targeted crashes were significantly reduced.

Retting said researchers didn’t set out just to improve Leesburg Pike. “We wanted to create a model for local officials nationwide to improve safety and traffic flow in their own areas. Officials can systematically study their arterials and identify problems. They should seek remedies besides the ones we’ve spelled out for Leesburg Pike because every urban arterial is different.”

Retting and his colleagues initially gathered reports over three years on crashes that had taken place at 14 intersections along six miles of Leesburg Pike and sorted them by location. Next the researchers classified the crashes according to type (a vehicle was struck by oncoming traffic during a left turn, a motorist failed to heed a traffic signal and collided with another vehicle, a motorist moved out of a travel lane and collided with another vehicle, or a stopped or very slowly moving vehicle was struck in the rear).

Where specific types of crashes were clustered at particular intersections, the researchers calculated the projected numbers of such crashes, relying on data from the whole arterial, to determine if a crash type was overrepresented. This revealed six problem intersections where crashes of a specific type were occurring more often than expected.

The researchers inspected police crash reports and observed the six intersections where crashes were clustered to see why the excessive crashes were occurring, and to identify countermeasures.

As an example, westbound motorists on Leesburg Pike used to have difficulties turning left across several lanes of heavy traffic at the intersection with Lewinsville Road. The speed limit for oncoming traffic is 45 mph, so vehicles often would proceed to the intersection at relatively high speeds. To make for more of a challenge, the view of oncoming traffic often is obscured by eastbound vehicles, including trucks and buses waiting to turn left.

In order to fix the problem, yet not break the bank, the Virginia Department of Transportation installed a protected left-turn signal for westbound motorists and adjusted the timing of the signal light for a smoother traffic flow.

Prior to the adjustments, westbound motorists at Lewinsville Road had been experiencing an annual average of 4.6 left-turn crashes. Over the next 31 months, not one such crash occurred.