The Virginia Department of Transportation is deploying variable speed limits to help manage congestion on the Capital Beltway when lanes are closed for construction in the approaches to the Woodrow Wilson Bridge. By adjusting speed limits, VDOT hopes to reduce the funnel effect that causes blockages, reports Sarah Karush for the Associated Press.
When a road narrows, or when lanes merge, smoothly flowing traffic typically bunches up. The chances for sideswipes and rear-end collisions increases as well. Using an analogy of rice pouring through a funnel, VDOT officials contended that if grains of rice (or automobiles) traveling through a funnel flow more slowly, they can get through it without bunching up and clogging the narrow gateway.
Traffic operators monitoring the Beltway traffic with cameras and sensors will raise and lower the speed limit in increments of 5 to 10 miles per hour. Initially, VDOT plans to use the technology only during nighttime lane closures associated with the Woodrow Wilson Bridge construction project. If it’s successful, officials hope to deploy it during the day as well.
Ultimately, the variable-speed strategy could be used around Northern Virginia both for recurring congestion and incident management — possibly even in locations like Tysons Corner where there aren’t any land closures but a large number of drivers try to get onto the highway all at once.
Bacon’s bottom line
: Kudos to VDOT. The Woodrow Wilson Bridge experiment could acclimate drivers to the paradoxical notion that driving at slower speeds can actually reduce congestion and get drivers to their destinations faster. It can also demonstrate the degree to which the operators of the Beltway HOT lanes, for which construction has recently begun, can keep tolled lanes flowing freely under dynamically changing conditions.