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

Spending a small amount of money on busy roadways in cities can lead to the ultimate goal of reducing the number of crashes reports a recent study from the Insurance Institute for Highway Safety. Recently released statistics show that while deaths on America’s roads are down, more work still needs to be done.

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 Highway Traffic Safety Administration.

According to statistics, the majority of crash deaths occur on rural roads, but 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. So what is being done to cut down on these types of road deaths?

Richard Retting, senior transportation engineer at the IIHS, noted in a report released last month, “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, Virginia, near Washington, D.C.

The researchers analyzed traffic on Leesburg Pike, noted problems that were causing crashes, and then put forth measures like adding 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 reportedly significantly reduced.

According to Retting, researchers didn’t set forth 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 reportedly revealed six problem intersections where crashes of a specific type were occurring more frequently than expected.

The researchers then inspected police crash reports and observed the six intersections where crashes were clustered to see why the excessive crashes were occurring. Were rear-end crashes occurring because turning vehicles weren’t adequately accommodated? Was the sight distance adequate to make a turn safely?

Asking these kinds of questions made for identification of necessary countermeasures. As an example, westbound motorists on Leesburg Pike reportedly 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 reportedly obscured by eastbound vehicles, especially trucks and buses waiting to turn left. These factors added to an overrepresentation of potentially serious side impacts involving left-turning vehicles.

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.

Similar measures were applied at another road, with equally dramatic results–an average of 8.7 left-turn crashes before the interventions were reduced to zero during the subsequent two years.

With this information in their hands, officials hope to use this analysis in other parts of the country to reduce traffic accidents, which will also bring a reduction in costs for all drivers.

According to an earlier NHTSA estimate, highway crashes cost society $230.6 billion a year, about $820 per person.