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Roundabouts: Making Busy Intersections Safer

Public officials are considering roundabouts as a solution for better safety and more efficient traffic flow at intersections in the Lehigh Valley. While roundabouts aren’t currently very common in the area, it’s important to realize how they can improve traffic flow and provide for safer driving conditions.

Modern roundabouts are not to be confused with large traffic circles, like the one Clark Griswold couldn’t seem to escape in “European Vacation.”

What exactly is a roundabout?

A roundabout is a type of intersection, where traffic flows almost continuously in one direction around a central island. As described by the Federal Highway Administration (FHWA), the essential characteristics of roundabouts include:

  • Counterclockwise Flow: Traffic travels counterclockwise around a center island.
  • Entry Yield Control: Vehicles entering the roundabout yield to traffic already circulating.
  • Low Speed: Curvature that results in lower vehicle speeds, generally 15 to 25 MPH, throughout the roundabout.

The FHWA estimates roundabouts reduce severe (injury/fatal) accidents by 78 to 82 percent and overall accidents by a factor of 44 to 48 percent. The FHWA also estimates that roundabouts increase traffic flow and capacity by 30 to 50 percent.

Benefits of Roundabouts:

  • Reduce queuing and permit U-turns within the normal flow of traffic, which are often not possible at traditional signalized intersections.
  • Accommodates vehicles of all sizes; including emergency vehicles, buses, farm equipment, and semi-trucks with trailers. When traveling through a roundabout you should give large trucks extra space, as they may straddle both lanes while driving through a multi-lane roundabout.
  • Designed with a truck apron, a raised section of concrete around the central island that acts as an extra lane for large vehicles and vehicles with trailers. The back wheels of the oversize vehicle can ride up on the truck apron so it may easily complete the turn, while the raised portion of concrete discourages use by smaller vehicles.

Marshalls Creek Traffic Relief Project

The best way to get comfortable with roundabouts is to drive through one. In 2014 PennDOT constructed the first roundabout in the area as part of the Marshalls Creek Traffic Relief Project. The State Route (SR) 209 Marshalls Creek Traffic Relief Project was a design-build highway bypass project constructed by Leeward Construction with Borton-Lawson as the lead engineer on the team.

The project was completed in the fall of 2014 with a total construction cost of $18.2 million. To help alleviate traffic congestion through the Village of Marshalls Creek, Borton-Lawson designed the first modern, two-lane roundabout for the Pennsylvania Department of Transportation Engineering District 5-0 (PennDOT 5-0), which is the local district that covers the Lehigh Valley area.

The Marshalls Creek Roundabout is a gateway to the new SR 209 bypass. It redirects traffic around the village of Marshalls Creek, while also providing access to business route 209. This traffic solution was the first-of-its-kind in the district, and introduced the viability of modern roundabouts to the traveling public.

Using design-build methodologies, the team was able to keep the project on its original schedule and implemented cost-saving opportunities. The bypass now serves approximately 23,000 motorists per day. The project received a 2015 Diamond Award for Engineering Excellence certificate from the American Council of Engineering Companies in Pennsylvania. PennDOT District 5-0 endorsed the project for submission to ACEC Diamond Awards, indicating that “the design consideration, met and exceeded our needs for the project.”

South Valley Parkway Project

While the Marshall’s Creek project was under construction, Borton-Lawson was completing the design of the South Valley Parkway Project. This project for PennDOT District 4-0 is located in Luzerne County and involves the design of 3 miles of new roadway, including six roundabouts, to connect Luzerne County Community College and the South Valley area, which is the city of Nanticoke, with SR 29, a limited access four-lane highway. Borton-Lawson is the prime engineering consultant for the project requiring completion of alternate alignment studies, environmental inventories, and all preliminary, and final design activities.

Extensive public involvement was required during the project development. This included open house style public meetings with attendance in excess of 200 people and conception and implementation of a project advisory committee (PAC). Presenting simulated models that show how the traffic will flow through the roundabout and general information about vehicular and pedestrian safety are were key components in gaining public support.

Borton-Lawson completed the design of the South Valley Parkway project in time for the November 2015 letting of the project. The winning contractor was Kriger Construction at a low bid of approximately $57.2 million which was within 2.4 percent of Borton-Lawson’s estimate for the project. The project has started the construction phase and is planned to be completed by the summer of 2020.