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


Use of Shoulder Allows for Lengthened Merge

The traditional approach to widening northbound I-279 merging into I-79 north of Pittsburgh would have called for expensive environmental and noise studies, plus expensive earthwork and out-year construction. Two-lane northbound I-279 merges into one lane prior to that lane continuing as the third lane on I-79. The traffic volume and the friction from merging were causing a routine bottleneck. Rather than pursue a time-consuming and expensive facility redesign, PennDOT chose to convert the existing right shoulder on I-79 to a 2200-foot fourth freeway lane, allowing for I-279's two lanes to flow into I-79 unencumbered. The now-four lane I-79 is merged back to three lanes further downstream, at a point where I-79 goes from a cut section to a fill section. The solution is low-impact and low cost. The work entails milling and resurfacing of the former shoulder, plus restriping. The estimated cost is $550,000. By constructing a new 12-foot shoulder, a design exception is not required. The project is expected to be fully completed in 2009, years ahead of what normally would have been a multi-year analysis, redesign, and reconstruction of much of the interchange.

Update (December 2009): This project is now open and solicited this unedited testimonial to PennDOT from a citizen: "This project has almost entirely eliminated the constant traffic back-ups at the merge point. You and your team must be very proud that your design has been validated by the results. Thank you very much."