One of my favorite pastimes is serving as a mentor for the Civil and Environmental Engineering Department’s Senior Design Project Program at the University of Pittsburgh each semester. During my academic career there, I was heavily involved in the program; since my retirement I have been privileged to participate in a greatly reduced role.
Transportation Engineering is one of the major disciplines within the Civil Engineering profession. Each year we have a few teams interested in projects appropriate to it. I carefully followed the construction of the roundabout at Pine Bridge Mall on McLaughlin Run Road and have been quite pleased with the results since it opened. I am also well acquainted with the awkwardness of the Bank Street/Lesnett Road/Mayview Road/Chartiers Street intersection, particularly since the Upper St. Clair traffic heading down Chartiers to the I-79 interchange has increased dramatically.
Consequently, as we were brainstorming ideas for project ideas for the current semester, I suggested we have a team study the possibility of constructing a roundabout at that location, a project that is complicated by the fact that Lesnett Road and Chartiers Street are offset by ninety feet, requiring a left turn onto Bank Street followed by a sharp right turn. The suggestion was strengthened when I learned that Bridgeville’s “Active Transportation Plan” included an initiative to “explore feasibility of roundabout or other intersection alternatives” for the intersection.
Sure enough, once the term began, a strong team of four students decided to take this on as a project. Fortunately, their mentors included two members of the Transportation faculty with experience implementing this type of project and navigating the PennDOT approval process. This was essential, as all four roads leading into the intersection are State highways. The fact that the team was able to complete the project in four months is a credit to the students and their mentors.
The first step in considering any improvement to a PennDOT intersection is a “warrant analysis”, the confirmation that some attributes exist that warrant a change. One attribute is crash data; Although fifteen crashes were reported at that intersection in the past five years, that was insufficient to warrant improvement.
Another attribute is traffic volume. The students had access to traffic counts made in 2019, that reported peak hour traffic of over 1500 vehicles per hour (one every 2.4 seconds). To confirm the credibility of these data today, they performed their own traffic counts during 2023 peak hour periods. Based on the maximum four-hour volumes observed, a change (adding signals or a roundabout) is warranted.
A powerful tool for understanding the flow of traffic in infrastructure networks is multi-modal traffic simulation software. Once the analyst models the intersection and inputs average anticipated traffic volumes, the software graphically shows the interaction of traffic on each leg and calculates “Level of Service” (delay times). Using this tool, the students soon confirmed the inherent problems with this intersection, particularly with the Chartiers/Lesnett through traffic.
Once the team had confirmed that an improvement was warranted, they studied three alternatives. Two of them involved the addition of traffic signals. The “two-phase” option alternated Bank/Mayview signals with Chartiers/Lesnett ones. The “three phase” option kept Bank/Mayview but split up Chartiers and Lesnett. The final alternative was a roundabout.
Many factors influence the decision process for selecting the appropriate alternative. The team developed a qualitative decision matrix which considered twelve equally-weighted “design factors”. They then assigned a one-to-five value for each factor and each option, added up the values, and concluded that the roundabout alternative should be recommended. Its strong points were queue time, safety, operating and maintenance costs, environmental impact, and aesthetics; its weak points were initial cost, construction time, and traffic delay during construction.
Development of the roundabout design determined that a single lane, sixteen feet wide, with an outer diameter of one hundred feet, would be suitable for the anticipated traffic volume. To accommodate the Chartiers/Lesnett offset, the team elected to center the roundabout slightly east of the existing interchange and to insert reverse curves into all four approaches. The resulting configuration appears to be an acceptable compromise.
The construction management plan for the project has split it into two distinct phases, to minimize the impact of construction on existing traffic. The first phase is the eastern (Lesnett Road side) half of the roundabout. During its construction, Lesnett Road traffic is detoured via Sarah and Winfield Streets while it is maintained on the other three legs. During construction of the western (Chartiers Street side) half, Chartiers Street traffic can follow the same detour and use the completed half of the roundabout to access Mayview Road. The hypothetical starting date for the project is in 2026, after PennDOT completes its current Chartiers Street project. The team anticipates a duration of about eight months.
The estimated cost of this project is $2,175,000. This estimate is based on quantity takeoffs from the proposed design and unit costs from the PennDOT ECMS data base, which includes data from the McLaughlin Run Road roundabout.
The students met with the Bridgeville Planning Commission in March to acquire feedback on the community’s interest in such a project; they will return this month to present their recommendations.
It must be emphasized that this specific project is the product of a group of University students, performed as part of a requirement for a specific University course, without any formal review by a licensed professional engineer. We hope its content will influence Bridgeville Borough, Upper St. Clair Township, and PennDOT to seriously consider a roundabout as an upgrade to this intersection.