Using Weather Information to Reduce Accidents and Improve Traffic Flow

The Trouble Spots

The Oregon Department of Transportation (DOT) manages over seven thousand miles of roadway throughout the state. Like most Departments of Transportation, Oregon's road network has its trouble spots – locations where accidents are more common due to congestion or weather-related incidents.

Just southwest of Portland, Oregon, there is a state highway that connects U.S. Route 26 and Interstate 5. This state highway, Oregon Route 217, has numerous interchanges where drivers are moving on and off the system, and these interchanges are close together. Because of the on and off volume of traffic, speeds often vary near the entrance and exit locations. It is not uncommon for rear-end crashes to occur near the interchanges. Further, where Oregon Route 217 (OR 217) and U.S. Route 26 intersect, there are curved ramps. When wet or icy these ramps are troublesome for drivers moving too fast. Vehicles slide off the roadway in adverse weather conditions because they are not prepared for the conditions and lose grip.

Implementing Driver Notification

Oregon DOT wanted to ensure the corridor was safe for drivers, and that they were properly notified of speeds and weather conditions along the route. The first location to be addressed was the trouble spot at the intersection of OR 217 and U.S. Route 26.

At three of the ramps in this interchange, where the roadways curve, Oregon DOT placed two Vaisala roadway weather systems, one on each side of the highway. The weather systems provided pavement temperature, condition, visibility, and a grip value. The grip measurement provided a numerical value to indicate how slippery conditions were for drivers and allowed the DOT to monitor if conditions were deteriorating or improving.

Dennis Mitchell, Region 1 Traffic Engineer and ATMS Program Manager with the Oregon DOT, commented, "Accidents on the ramps were almost always a result of weather conditions." The weather systems at this intersection were installed to warn drivers of conditions and reduce accidents. The Oregon DOT knew they wanted to use pavement condition information because it could be used to activate warning signs. Using an algorithm based on conditions reported from the Vaisala weather systems, message signs activate and notify drivers to slow down on ramps. "It worked very well," Mitchell added.

The other trouble spot to address was the main corridor of OR 217. An automated system to notify drivers about changing speeds through the main corridor was planned, and with the successful application of weather information at the OR 217 and the U.S. Route 26 junction, a grant from the Federal Highway Administration (FHWA) allowed Oregon DOT to add weather information and modify the software program used to activate the signs. "FHWA wanted [Oregon DOT] to test the weather information in the corridor, and see if would make a difference for drivers," Mitchell noted.

Two additional Vaisala weather stations were placed along the corridor, again monitoring weather and grip conditions. The software and algorithms were modified to address both traffic speeds and weather conditions. The system continuously monitors weather and traffic congestion, and whichever has the largest effect to drivers is used to activate automated message signs. With timely information, drivers can quickly react and to slow down to avoid an incident.

Ensuring Safe & Smoother Traffic Flow

Oregon DOT realized the results of the curve warning system and corridor weather stations right away. Having weather information along the corridor, and being able to notify drivers based on conditions, reduced crashes by nearly 21%. Further, there was a significant reduction in the severity of incidents, and throughput increased by 5% during commute times. Throughput is the number of vehicles passing through the corridor, an indication of improved efficiency. Corridor reliability also improved, with average daily variability in travel times decreasing by 10%. Using traffic and weather information together, Oregon DOT was able to improve service to drivers in their state and ensure safer travel with improved traffic flow.

Vaisala's web resource on sustainable road maintenance is especially targeted towards the highway and street authorities. We want to provide tangible solutions on how to condition roads in a sustainable, yet safe manner.

Sustainable Highways

By Jonathan Tarleton, Head of Transportation Marketing, Vaisala

Late last year Vaisala launched a web resource for our highway and street authorities around the world. This resource is meant to grow and change as new materials and reports are generated, giving the authorities key facts, figures, and strategies on how to ensure their operations are sustainable. In winter road maintenance, we can look at sustainability in terms of the impact on the environment and/or having enough resources to fund and maintain a level of service that equals our societal rewards.

Winter road maintenance is all about balancing effort with impact. If you live in an area that receives snow and ice your road agency could decide not to use road chemicals to help the environment; however, at the same time, not using these chemicals can have a similar negative impact on the environment. Crashes or stopped traffic, for example, can cause environmental issues as well. Road crews could also apply so much chemical to the road that it is nearly impossible for snow or ice to freeze to the roadway, but this is obviously not good for the environment, the road network infrastructure, and it is not even necessary. Most road chemicals, like salt, are mined from the earth so how can they be bad? They are not when used in moderation, but when used in excess even salt can become very damaging to the ecosystems of the nearby bodies of water, our drinking water, or the infrastructure of our roadways and bridges.

The truth is, the entire concept is nothing new for winter road maintenance, is it? They apply chemicals and manpower to a road network to keep people, goods, and services flowing, and although maintenance vehicles and chemicals can viewed as a negative environmental impact, what about pollution from gridlocked traffic, or crashes that spill fuel and oil? It is all about balancing our efforts with our rewards. Today, municipal governments, road authorities, and even entire countries are being asked to make sure they are sustainable. This resource can guide our customers to ensure they are doing everything they can, and are able to communicate the sustainable actions they are embarking on.