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Why roundabouts? PennDOT says safety

For those who prefer a more mathematical approach, here (photo below) is a breakdown of the two types of intersections as far as of the potential conflict points, or spots/angles where vehicles and/or pedestrians could meet.

When it comes to intersection improvement projects, the Pennsylvania Department of Transportation (PennDOT) is diligent and deliberate in our planning process. This includes the design of possible changes at the intersection of Pennsylvania Avenue and Market Street in the City of Warren.

Two alternatives have been proposed for that location — an upgraded signalized intersection and a roundabout. The latter proposal has garnered lots of attention and questions, many of them involving how pedestrians and large trucks would navigate the roundabout.

Let me first say that PennDOT officials are frequently asked why we build roundabouts. The answer is simple — safety.

Improved safety extends to motorists of p

assenger vehicles and semi-trucks, bicyclists, and pedestrians using the intersection. When comparing a single-lane roundabout to a signalized intersection, studies show that roundabouts experience a 90 percent reduction in fatal crashes, 75 percent fewer injury-causing crashes, a 30-40 percent decrease in pedestrian crashes, and a 10 percent decline in bicycle crashes.

These conditions exist primarily because roundabouts have fewer points of conflict, slower traffic speeds, flared entry, and offer easier decision-making compared to an at-grade, signalized intersection.

James Foringer, P.E., is the District Executive for PennDOT’s northwest region, which includes Crawford, Erie, Forest, Mercer, Venango, and Warren counties. He has held various positions within PennDOT during his 33 years with the department.

Splitter islands (traffic dividers), truck aprons, and right-hand-only turning movements are other attributes of roundabouts that increase safety while preserving the ability for even oversized-loads to travel through the intersection without difficulty.

Concerning the Pennsylvania Avenue and Market Street intersection, many residents have reached out to PennDOT with questions about pedestrian safety. Roundabouts have several features that increase pedestrian safety versus an at-grade, signalized intersection. These include the following:

*All entrances to a roundabout are yield conditions for motorists, who are always turning right.

* The crosswalks are set back from the actual roundabout one or more car lengths, therefore, pedestrians crossing areas are not at the same location as vehicle entry and exit points into and out of the roundabout.

* Pedestrian refuge areas within the splitter islands provide walkers the ability to cross one direction of approaching traffic at a time. Therefore, the distance a pedestrian must cross is only 18 feet of roadway at a time.

* Numerous traffic signs are posted indicating the need for drivers to yield and that there are crosswalks and a roundabout ahead. Traffic must slow down to navigate a roundabout, so motorists are more likely to follow the Motor Vehicle Code and yield to pedestrians at crosswalks.

* The design of the intersection slows traffic entering, traveling through, and exiting the roundabout. Since there aren’t traffic signals and the location of the crosswalks are away from the circle, means drivers can focus their attention on the movement of pedestrians and other vehicles at the intersection.

* The truck apron in the center of the roundabout gives additional space for large vehicles and truck trailer tires to use to navigate the roundabout.

For a signalized intersection at a similar location, a pedestrian often must contend with the following conditions:

* Drivers going in multiple directions depending on the lights, including right-hand and left-hand turns.

* Pedestrians are crossing at the corner where motorized traffic is also entering the intersection and possibly turning right or left, or going straight.

* A pedestrian is at the corner where the roadway is the widest and, therefore, must cross 11-12 feet per lane. At the intersection of Pennsylvania Avenue and Market Street, the design may include four or five lanes for eastbound and westbound traffic. That means a pedestrian must cross up to 60 feet of roadway at one time rather than 18 feet.

* Because there are multiple lanes, drivers approaching the intersection would be between 12 to 36 feet from any permanent Yield to Pedestrian signs. Yield to Pedestrian Channelizers, which typically sit in the crosswalk, would not be considered at this intersection because of the high volume of truck traffic.

* Based on the signals and traffic volume, drivers will be traveling through the intersections at varying speeds. Unfortunately, some motorists drive quickly as they approach a signalized intersection in an attempt to “beat” the red light. This causes their focus to be up on the light instead of on the movement of vehicles and pedestrians.

* Tight turning radius means larger trucks are unable to stay in their designated lane, or additional space must be designed into the intersection.

For those who prefer a more mathematical approach, here (photo below) is a breakdown of the two types of intersections as far as of the potential conflict points, or spots/angles where vehicles and/or pedestrians could meet.

For a roundabout, there are eight potential conflict points for vehicles and eight for pedestrians. In a typical signalized intersection, there are 32 potential conflict points for vehicles and 24 for pedestrians. The illustration below shows those points of conflict.

The abovementioned safety features are among the chief reasons PennDOT considers roundabouts whenever preparing for an intersection improvement project, but there are additional benefits as well.

Roundabouts offer increased traffic capacity and efficiency. A single-lane roundabout can typically carry 30 percent more vehicles than a similarly sized signalized intersection during peak flow conditions. This is due to the continuously flowing nature of yielding only until a gap is available versus waiting at a signal. These benefits – slower speeds, natural breaks in traffic, increased efficiency — can also extend throughout the corridor where a roundabout is located.

There is potential for money savings for the city and motorists through the construction of a roundabout. The decreased wait times entering and exiting the roundabout versus sitting at a red light can lead to savings in gasoline consumption. For the municipality, funds are no longer needed to power and maintain electrical signals, and municipal maintenance of the roundabout is minimal.

Even with the increased safety, efficiency, and capacity of roundabouts, they aren’t the best fit for every intersection. Therefore, careful consideration is necessary as part of the planning and design process.

It should be noted that construction of roundabouts in the U.S. started in the early 1990s and in Pennsylvania in 2005. Roundabouts should not be confused with the older-style traffic circles.

PennDOT continues to discuss the design of the intersection at Pennsylvania Avenue and Market Street with the officials and residents of Warren.

We encourage community members to go online and check out a digital copy of the presentation given on August 22. It is posted at www.penndot.gov/district1 under the District Links heading.

Additional information on roundabouts, including educational videos, is also available online at www.penndot.gov by clicking on the Roundabout link located under the FEATURED RESOURCES heading on the homepage.

James Foringer, P.E., is the District Executive for PennDOT’s northwest region, which includes Crawford, Erie, Forest, Mercer, Venango, and Warren counties. He has held various positions within PennDOT during his 33 years with the department.

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