Office of Operations
photos of traffic merging onto congested highway, congestion in snowstorm, variable message sign, cargo, variable speed limit sign in a work zone, and a freeway at night
21st Century Operations Using 21st Century Technologies

Traffic Bottlenecks

Combating Bottlenecks


Erasing a high-accident, high-delay "no acceleration lane" merge by using available shoulder to create one.

Background Project: Carnegie Interchange (Academy Street at I-279). The ramp from Academy Street to I-279 SB was a high-accident, high-delay location for years. The primary reason was the lack of an acceleration lane at the top of the ramp. Vehicles had to come to a complete or near-complete-stop before merging onto I-279. The mainline is two-lanes at this point, and widens to three lanes approximately 800 feet downstream. The solution, currently under design and implementation for Fall, 2007, will be to convert the mainline shoulder to a full-length acceleration lane allowing at-speed merges. Further, the lane will tie into the third lane of the mainline downstream. The solution is low impact and low cost (estimated repaving, restriping and resigning is $250,000). Despite losing the shoulder through these limits, it was determined that the benefit-gain outweighed the safety risk, especially when compared to the prior, worse, safety condition.