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It’s a design that has long been a trademark to many a historic downtown, but the modern design of the traffic roundabout is becoming a more and more common sight in Pennsylvania.

Construction began last week in Middlesex Township and Perry County on a roundabout at Sterretts Gap, which is the intersection of Route 34, Mountain Road and Sunnyside Drive. It will be first modern roundabout in Cumberland and Perry counties and one of a few in the Midstate — there are two others in York County, two in Linglestown, one in Campbelltown, Lebanon County, and one in Abbottstown, Adams County. PennDOT estimates there are 16 built on a state-owned road in Pennsylvania and four others built in local roads.

About five other roundabouts in the state are already under construction.

That is a big jump from when Pennsylvania — and the rest of the country — started looking at roundabouts as a viable option for intersection design, said Jeff Bucher, project development engineer at PennDOT and roundabout coordinator for the state.

“The modern roundabouts started being built in the country in the mid 1990s,” he said. “Maryland started before we did. They have 150 roundabouts now. So, we’re actually, for our area, late adapters of the roundabouts. I think our first roundabout in the state was in 2005.”

Bucher explained that the modern roundabout is a little different from those in historic downtowns, such as in New Bloomfield and Gettysburg.

“At the Gettysburg Square, that’s an old-style traffic circle with parking,” Bucher said. “(Modern) roundabouts are small and accommodate vehicles. It is not supposed to have parking.”

Pedestrian traffic is also slightly different. Modern roundabouts do not allow pedestrians to travel to the center of the circle, but rather are built to have them use crosswalks, sidewalks and islands at the entrance/exit of each road into the roundabout.

Bucher said the modern roundabouts mostly are constructed at intersections with a high traffic volume. The single-lane roundabout can be used for intersections that have about 25,000 average daily travel vehicles, though double-lane roundabouts can also be instructed for higher volumes of traffic, Bucher said.

Safety

There are two major reasons for construction of a roundabout — safety and traffic.

It’s the former that was an area of concern for Middlesex Township Police with the Sterretts Gap intersection. Middlesex Sgt. Steven Kingsborough said the department has responded to a number of crashes at the intersection — including some that were fatal.

“The accidents that we’ve had up there are not minor,” he said. “They’re reportable, which means there are injuries are a vehicle has to be towed.”

Kingsborough said the intersection involves speeds of 45 mph on Route 34 (Spring Road), and those trying to merge from Sunnyside Drive onto Spring Road often never saw the vehicle on Spring Road until it was “on top of them.”

PennDOT said Sterretts Gap had a crash rate higher than the statewide average for similar intersections. It attributed that to poor roadway geometry and lines of sight. Angle crashes and rear-end crashes together accounted for 69 percent of reportable crashes and 57 percent of non-reportable crashes at the intersection, which handles about 15,000 vehicles per day.

In the 28 years he’s worked at the department, Kingsborough said he’s seen two changes to that intersection. One involved installing a left turn lane on Spring Road heading to Sunnyside Drive. That cut back on the traffic that would back up on Spring Road when someone was attempting to turn left, but it hasn’t solved the issue, he said.

The roundabout currently under construction aims to reduce angle-type crashes and reduce the severity of future crashes.

Bucher explained that speeds in the roundabout are much slower than those at a normal intersection, so the 45 mph speeds on Spring Road would be reduced closer to 20 to 25 mph. Slower speeds mean less severe crashes, and PennDOT said roundabouts can provide a 90 percent reduction in fatal crashes, 75 percent reduction in injury crashes, 30 to 40 percent reduction in pedestrian crashes and 10 percent reduction in bicycle crashes.

Those are the kinds of statistics Kingsborough said they are hoping to see once the roundabout opens by the end of the year.

“We’re hoping it cuts down on serious accidents,” he said.

Traffic

In the village of Linglestown in Lower Paxton Township, it wasn’t crashes which concerned officials, but rather the sheer amount of vehicles traveling through the area.

Built in 2011, Linglestown has two roundabouts within 3/4 a mile from each other, which had been in the planning process for quite some time.

“The planning evolution stretches back to 1994,” Lower Paxton Township Manager George Wolfe said. “We had different concepts for the intersection ... (but the roundabout plans) came through in 2006. From that point, we began design.”

Wolfe said what the township and Linglestown wanted was for safer travel for residents walking around the downtown area.

“There are more than 16,000 vehicles every day driving that road,” he said. “This led us to look at a solution and still provide for traffic mobility and save our flagpole (at Linglestown and Mountain roads).”

Wolfe said there used to be 300 to 400 feet of backlog traffic — more during rush hour — on Mountain Road. All of that, however, has disappeared after the construction of the roundabout.

“It’s non-existent,” he said. “With the roundabout, the traffic keeps moving. Route 39 (Linglestown Road) is a direct route to Central Dauphin High School. Even with the school traffic in the morning, it flows through — maybe slower because the speed is 25 mph.”

PennDOT said roundabouts can help traffic capacity, typically carrying about 30 percent more vehicles than a similarly sized intersection during peak traffic hours.

Truck traffic

Even with the benefits, there are some limitations.

Bucher said most modern roundabouts are designed to handle large-vehicle traffic, such as tractor-trailers and emergency vehicles. However, the diameter of a roundabout varies on the amount of space available.

The two roundabouts in Linglestown are smaller than other designs because of the room that was available. Greg Penny, spokesman for PennDOT District 8, said “urban” roundabouts are tighter because making the intersection any bigger would result in a loss of some of the downtown and neighboring property.

With a smaller roundabout, however, it means it is difficult for Linglestown to handle tractor-trailer traffic.

Wolfe said it is a myth that school buses couldn’t make the turn when the roundabouts first opened, but the township had major problems on their hands last May when a tanker crash and fire severely damaged Interstate 81 at Route 322 in Dauphin County.

Ordinarily, tractor-trailer drivers are told to stay off Linglestown Road, but the road ended up being the one detour for all of the traffic in that incident.

“That was an unforeseeable circumstance,” Wolfe said. “Nobody was happy about that.”

On a whole, though, Penny said roundabouts can handle tractor-trailers and have special design features — truck aprons — to help make sure the tractor-trailer makes it around the roundabout, even if driven a little off-course. Penny explained that the truck apron around the circle of the roundabout is built to allow the rear wheel of the trailer to go up over the concrete without getting stuck in the middle.

Future

Since the construction of the Linglestown roundabouts, Wolfe said he considers the results a success with what they were looking to achieve.

“Once you got through the initial six months of people learning how to drive them, it was fine,” he said. “It works famously.”

Penny said having a roundabout instead of a traffic signal — which is usually the only other option — is more cost effective in the long-run. He said signals have a long-term cost for maintenance of the signal, electricity and other regular maintenance at the intersection. Roundabouts, however, are not as costly to maintain.

“There is a higher initial cost because of construction,” he said.

The construction cost of the Sterretts Gap roundabout is about $2.1 million.

That roundabout won’t be the last in the Midstate. The Carlisle Urban Redevelopment plans call for a roundabout at Carlisle Springs Road, North Hanover Street and Kerrs Avenue — though that is still in the planning phases.

Bucher said there is also discussion on incorporating modern roundabout design into interstate exit ramps. He explained that instead of drivers exiting an interstate and hitting a traffic signal, they could encounter driving into a roundabout that could alleviate traffic.

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