This summer, the Washington State Department of Transportation (WSDOT) will begin installing overhead electronic signs on northbound Interstate 5, State Route 520 and Interstate 90 between Seattle and Bellevue. The signs are a key component of the WSDOT Smarter Highways program, which uses real-time traffic information to improve safety and reduce congestion.
No commuter will disagree with the fact that our highways are congested. Many factors contribute to increased travel times. In fact, more factors contribute to congestion than an average commuter might realize.
Most know that daily increases in traffic volume result in congestion, as do accidents, last-second merging, and differences in vehicle speeds.
Traditionally in the United States, the solution to congestion has been to increase the number of lanes. Realistically, however, this is an expensive solution that usually does not permanently solve the problem.
Each continuous lane has a maximum capacity of about 2,200 vehicles per hour. However, adding lanes encourages more drivers to use the roadway, hindering congestion relief. Relying purely on additional lanes for congestion reduction will lead to only temporary relief.
In fact, more lanes lead to lower capacity per lane. The relationship between the number of lanes and the capacity per lane is not linear. With each additional lane, the capacity per lane decreases due to more complex traffic patterns. This includes a higher rate of lane changing and an increased probability of accidents.
Relying solely on additional lanes for congestion relief is not only expensive, but in many ways counterintuitive. There is an inverse relationship between the number of lanes and efficiency.
In the past few years, the Washington State Department of Transportation (WSDOT) has looked at factors that will help reduce congestion. WSDOT found that if drivers are aware of lane-blocking accidents downstream, they can reduce congestion by gradually merging into adjacent lanes and avoiding last-second forced merging and accidents, and when drivers know travel times in advance, they can select the fastest route and avoid contributing to already congested routes.
WSDOT research also found that if drivers traveled at a speed appropriate to traffic volume, roadway capacity can be maximized. Higher speeds decrease lane capacity, because the distance between vehicles increases.
But lower speeds also decrease lane capacity, because traffic takes longer to pass from point to point. The speed that optimizes capacity by allowing for maximum lane throughput is 45 miles an hour.
The solution to congestion is to improve awareness, manage capacity and control traffic flow.
