Golden Mile Highway Continuous Green T Intersection
Municipality of Murrysville and PennDOT District 12-0 Westmoreland County, PA
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Stahl Sheaffer Engineering, Inc. (Stahl Sheaffer) provided planning, design, and geotechnical services for the privately funded redesign and realignment of the intersection at the junction of traffic routes 286 & 380 (Golden Mile Highway & Saltsburg Road) in Murrysville, Pennsylvania, a complicated intersection with unique geometry. After a study determined that the intersection needed to be signalized, Stahl Sheaffer explored various alternatives to ensure the safest solution. A collaborative effort between Stahl Sheaffer, PennDOT, Municipality of Murrysville officials, municipal engineer, and other stakeholders ultimately ensured a successful project.
A design was recommended that allows the major direction of traffic on the main road to bypass the traffic signal and flow continuously, while other movements (such as left turns from Saltsburg Road) are managed by a traffic signal and channelized lanes. The continuous flow aims to improve traffic efficiency, reduce delays and fuel consumption, and enhance safety by minimizing potential angle crashes. |
Northbound View with Preexisting Condiitons
Northbound View on Golden Mile Highway at Turning Lane
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Aerial View of Completed Continuous Green T Intersection
View of Intersection from Saltsburg Road Bridge
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Complexity, Challenges, and Innovation
Stahl Sheaffer designed a “Continuous Green T (CGT) Intersection” whereby the major direction of traffic traveling straight through the intersection flows continuously without stopping, while other movements are managed by a traffic signal and channelized lanes. CGT intersections have been successfully used in Pennsylvania and many other states. The corridor along the Golden Mile Highway presented unique challenges with regard to two major traffic routes intersecting and bound tightly by existing land uses, terrain, highway structures, and access points. Applying a CGT intersection opposite an access break is difficult to achieve without re-location. Stahl Sheaffer worked with PennDOT to arrange a design that still accommodated the existing access point, maintained traffic during construction, and successfully applied an innovative CGT intersection to this location.
The intersection where Saltsburg Road meets the Golden Mile Highway presents unique geometry and, along with a history of aggressive driving, speeding, and sight distance challenges, resulted in angle crashes, near misses, and operational deficiencies (levels of service queuing). These issues were exacerbated by vertical geometry on Golden Mile Highway obstructing sight distance for cars approaching the intersection from the south.
The intersection where Saltsburg Road meets the Golden Mile Highway presents unique geometry and, along with a history of aggressive driving, speeding, and sight distance challenges, resulted in angle crashes, near misses, and operational deficiencies (levels of service queuing). These issues were exacerbated by vertical geometry on Golden Mile Highway obstructing sight distance for cars approaching the intersection from the south.
- The majority of traffic heading north crested a hill and passed under a low clearance bridge just prior to the intersection that obstructed the driver’s view of the roadway. These issues would also be compounded by a traditional traffic signal due to the speeding observed in data collection.
The high volume of northbound traffic continuing through no longer needs to stop for minor street traffic, avoiding unnecessary slowdowns. - The design should reduce the possibility for rear end collisions due to the continuous lane.
- Multiple numbered state routes intersect at various points in this area and in some cases overlap. Additionally, the numbered state routes differ from the SR numbers, created a possibly confusing scenario for drivers unfamiliar with the area.
- Single face barrier was utilized as retaining wall due to the steep terrain. This approach made the grading fit within the confines of existing right-of-way.
- Motorists entering traffic from a residential driveway also created a hazard.
Safety and Sustainability
The CGT intersection solution improves safety by avoiding unnecessary stoppages, which traditional traffic signals have a tendency of increasing. FHWA research suggests that CGT intersections reduce angle crashes 96.8%, injury crashes by 70%, and total crashes by 60%. In addition, field observations at the intersection following construction observed less queuing and delay from the Saltsburg Road approach.
Given the operational challenges of the existing intersection configuration, with multiple stops required for left turning vehicles onto Saltsburg Road, including at times through stopped traffic, the ability to keep moving provides a safer alternative.
New roadside safety barriers were also replaced through the project corridor to current MASH standards, replacing outdated systems of former years that were below standards.
Stahl Sheaffer’s solution supports sustainable travel along this corridor that impacts economic development and local travel. Aesthetics and sustainable benefits are a direct result of this project, including:
· The LED luminaries used in the traffic signals are brighter for better visibility which can decrease the number of accidents.
· LED traffic lights are much more energy efficient and durable.
· The post-construction seeding will better integrate the road into the surrounding landscape, increasing the aesthetics of the area.
· With reduced delays, the CGT design reduces fuel use.
· Subsurface stormwater and other appurtenances were designed to a 100-year life, which should reduce the potential for having to replace pavement prematurely.
Given the operational challenges of the existing intersection configuration, with multiple stops required for left turning vehicles onto Saltsburg Road, including at times through stopped traffic, the ability to keep moving provides a safer alternative.
New roadside safety barriers were also replaced through the project corridor to current MASH standards, replacing outdated systems of former years that were below standards.
Stahl Sheaffer’s solution supports sustainable travel along this corridor that impacts economic development and local travel. Aesthetics and sustainable benefits are a direct result of this project, including:
· The LED luminaries used in the traffic signals are brighter for better visibility which can decrease the number of accidents.
· LED traffic lights are much more energy efficient and durable.
· The post-construction seeding will better integrate the road into the surrounding landscape, increasing the aesthetics of the area.
· With reduced delays, the CGT design reduces fuel use.
· Subsurface stormwater and other appurtenances were designed to a 100-year life, which should reduce the potential for having to replace pavement prematurely.
Meeting and Exceeding Owner/Client Needs
The final design successfully addressed the stated complexity and challenges, providing not only continuous flow for the major traffic direction, but also a better alignment closer to 90° and greater efficiency since more green time can be provided to other movements, reducing corridor travel times. All of this was completed on schedule with the construction being completed in a single season. It should be noted that the selected alternative was not the most economical and cost-effective, however it was deemed to be the safest based on the operational characteristics of the corridor.
During construction, challenging conditions were encountered at the intersection. Excavation for the widening of Saltsburg Road exposed an existing stormwater inlet and pipes that were previously buried, and a field meeting was convened to work on a re-design. This work involved adding additional 100-year aluminum pipe, flowable fill, additional inlets; and grouting existing pipes that could not be removed.
Also, during the project, it was noted that the existing bridge drainage from Saltsburg Road overpass was causing significant erosion around the bridge piers. In discussions with PennDOT, it was ultimately decided to add riprap to the slopes to stabilize them. These changes were not reflected in the original bid amount but were added to this project while work was occurring.
Stahl Sheaffer maintained close communication during the project with the contractor, PennDOT, and municipal officials to advise them of changes to cost and schedule, while also ensuring that the best possible outcome was achieved (fixing it right the first time to avoid future maintenance challenges).
During construction, challenging conditions were encountered at the intersection. Excavation for the widening of Saltsburg Road exposed an existing stormwater inlet and pipes that were previously buried, and a field meeting was convened to work on a re-design. This work involved adding additional 100-year aluminum pipe, flowable fill, additional inlets; and grouting existing pipes that could not be removed.
Also, during the project, it was noted that the existing bridge drainage from Saltsburg Road overpass was causing significant erosion around the bridge piers. In discussions with PennDOT, it was ultimately decided to add riprap to the slopes to stabilize them. These changes were not reflected in the original bid amount but were added to this project while work was occurring.
Stahl Sheaffer maintained close communication during the project with the contractor, PennDOT, and municipal officials to advise them of changes to cost and schedule, while also ensuring that the best possible outcome was achieved (fixing it right the first time to avoid future maintenance challenges).
Funding Provided by
