Why Roundabouts?

As reported in the Flagpole, the mayor and commission is considering a new design for a roundabout at the intersection of Hancock and Broad:

Flagpole's article on the Broad Street roundaboutWith a roundabout already completed on Tallassee Road, one under construction on Whitehall Road and another being planned for Broad Street, Athenians might be asking themselves, “Why roundabouts?” Why do roundabouts suddenly seem popular with transportation planners in Athens? First, let’s look a little deeper to find out what a roundabout actually is.

What’s a roundabout?

A roundabout is a particular kind of circular intersection, and not just any ole traffic circle. Large, New England-style rotaries are not roundabouts. Small, neighborhood traffic calming circles, like the one on Boulevard, are also not roundabouts.

Modern roundabouts are distinguished from traffic circles or rotaries in that vehicles entering must yield to those already circulating inside. Roundabouts have the following features:

Schematic of roundabout design
From MikeOnTraffic.com.

This type of design has been popular in Europe for quite some time, and it’s catching on with American traffic engineers as well. But why?

Why roundabouts?

Safety

Single-lane roundabouts have 75% fewer points of potential vehicle conflict than do standard 4-way intersections. They also slow traffic and change the angle of potential collisions, making for a much safer roadway.

Potential conflict points for various intersection designs.
Potential conflict points for various intersection designs. Figure from the Institute for Road Safety Research.
Bar graph showing how roundabouts reduce collisions.
Data from the Federal Highway Administration, via the Washington State DOT.

Most importantly, roundabouts more or less completely eliminate the deadly “T-bone” type of collision that are relatively common at standard intersections. According to the Federal Highway Administration, this all adds up to enormous safety improvements, reducing fatalities by 90%, and overall collisions by 37%. Yes, there will still be accidents, but they tend to be minor.

These safety benefits apply to pedestrians as well. When crossing a roundabout, those walking only have to cross one lane at a time, and can rest on the splitter islands before crossing the next lane. One downside is that walking around a roundabout is generally a longer route than straight through a traditional intersection. Another drawback is for the vision-impaired, who unfortunately have difficulty crossing roundabouts on foot.

Efficiency and Speed

Drivers often worry about delays if standard intersections are changed to roundabouts, but I have good news! Roundabouts actually reduce traffic due to efficiency in design. Speeds are slower, but since fewer cars ever come to a complete stop, travel time usually decreases, in some cases quite substantially. In a 2005 study by the Insurance Institute for Highway Safety, researchers examined 10 signalized intersections in Virginia and estimated that, if constructed as roundabouts, vehicle delays would have been reduced by 62-74 percent.

Mythbusters did an episode on this and they also found that roundabouts actually improve intersection throughput and therefore would reduce traffic delays in most cases, similar to the data found by more scholarly researchers.

Other Benefits

Lower CO2 emissions: Roundabouts are more environmentally-friendly, reducing CO2 emissions from vehicles that would be idling at a stoplight in traditional intersections.

Lower maintenance costs: Once constructed, roundabouts require no electricity and are cheaper to maintain than signalized intersections.

The Proposed Broad Street Roundabout

The proposed design is a double-lane roundabout, which is not as good for safety compared to single-lane roundabouts. This is due to additional points of conflict that arise with drivers potentially changing lanes while looping around. Still, these conflicts would normally result in side-impact collisions at low-speeds, and would not normally result in fatalities. In my opinion, this new intersection would be much better than what we’ve got now, safety-wise, especially for pedestrians.

It’s important to point out that right now, there is no crosswalk at this intersection! People can be seen dashing across this multi-lane highway on a regular basis on their way to church, school, the farmer’s market or just the other side of the neighborhood. A crosswalk is essential at this intersection in my view. Since the proposed design will likely include flashing beacons for pedestrians, the safety improvements will be even more significant.

So, this roundabout design would add a badly-needed crosswalk and improve safety for those in cars as well. Furthermore, adding a double-lane roundabout to this intersection will reduce traffic delays by an estimated 80%, according to Drew Raessler, Director of Transportation and Public Works for Athens-Clarke County. Wow!

The roundabout would be funded with T-SPLOST dollars and with a contribution by the Georgia Department of Transportation (GDOT). With the state government chipping in, this project would seem a no-brainer to me, if not for the planned closing of The Plaza. The design is still in the conceptual stages, with a mayor and commission vote and several rounds of public input ahead. Hopefully, it will only be improved from here, but the design we’ve seen so far is already a win-win for both drivers and walkers.

The Mayor and Commission will vote on May 7 whether or not to allow Transportation and Public Works to continue the process of tweaking this design before it’s presented for public input. You can tell them what you think here (it’s agenda item #6).

Chris Dowd
Athens Politics Nerd
April 28, 2019

 

 

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