As transportation officials dig for cheaper, safer ways to improve both traffic flow and safety, there seem to be two trends proliferating at intersections. Local governments and the state DOT have constructed several diverging diamond interchanges (DDIs) at busy interstate interchanges in Metro Atlanta. Those are designed to eliminate left turns across oncoming traffic, a design which decreases wrecks and can improve the wait times.
Driving thru DDIs is different, but doing so requires very little maneuvering. Drivers simply follow their lane and have very little confusion about crossing to the other side of the road and then back again. The road does all the work for the motorist. Roundabouts, meanwhile, are showing up in more places in Atlanta, but they require a bit more effort and thought from commuters.
Roundabouts have been common in other countries and not just for small, neighborhood intersections. I’ve ridden through some intimidating roundabouts in Grand Cayman and Aruba that are fast, multi-laned, and confusing. But they are constantly moving. And that is the main reason that these intersections are popping up in more places in this metro area.
Much like DDIs, roundabouts keep traffic moving and eliminate left turns across oncoming traffic. By decreasing overall wait times and idling time at stop signs and lights and by lessening the likelihood of wrecks, roundabouts seem like a win-win. But they take adjustments from first-time navigators.
The first rule for traffic approaching a roundabout is that it must yield. All traffic outside of the traffic circle must yield to traffic inside it. It also must yield to pedestrians or bicycles in the crosswalks on each turn of the roundabout. This obviously is for safety purposes and to prevent any hesitation to the traffic flow. If drivers didn’t know which one had the preferred spot, more crashes would occur and the hesitations would cause more delays.
Roundabout confusion is greatest when they have multiple lanes. Multi-lane roundabouts are not common in Atlanta, but as more engineers embrace them, there certainly could be more of them. Roundabouts move one direction: counterclockwise. Drivers entering the traffic circle and progressing just one street over — what would be a right turn in a standard intersection — enter the roundabout in the right lane and then stay there until that first turn. Drivers that are going what would be straight or left would enter the roundabout in the inside or left lane and then turn from that lane onto their desired street. They keep moving and the drivers in that outside lane can continue moving, because they have a designated lane to make that turn, without interrupting the other vehicles. In a double-lane roundabout, the turns onto each street have two lanes: one for the outside lane vehicles and one for the inside lane. This allows seamless transitions, without cars stopping.
Quite possibly the golden rule of roundabouts is this: never change lanes. The lane in which one enters the roundabout is the one in which they stay until they exit. This is another genius innovation in this configuration. Eliminating lane changes means removing the friction they cause. Traffic simply keeps moving, until it exits the circle.
The lack of traffic lights at intersections also means more efficient traffic flow during non-peak times. Isn’t waiting at a light when there is no traffic a real annoyance? This isn’t a problem at all in roundabouts. Just proceed with caution.
One of the most noticeable roundabouts in Atlanta is that at Riverside Drive and I-285. GDOT recently converted that interchange from the standard traffic signal arrangement to a roundabout two years ago. This was done to try to make traffic off of busy I-285 somehow move better onto two-lane Riverside. Many people use Riverside to cut up to Johnson Ferry and commute into East Cobb. Unfortunately, the backup in PM drive from the right lane I-285/eastbound still stretches back about as far as it did with a traffic light. But, there are definitely very few crashes in the interchange.
Do not be intimidated by roundabouts. Just follow the few simple rules and embrace them. They are much more cost-effective ways to help traffic than stringing up signals and paving more lanes. But this is Atlanta and embracing the concept of traffic actually moving can seem foreign.
Doug Turnbull, the PM drive Skycopter anchor for Triple Team Traffic on News 95-5 FM and AM-750 WSB, is the Gridlock Guy. He also writes a traffic blog and hosts a podcast with Smilin’ Mark McKay on wsbradio.com. Contact him at Doug.Turnbull@coxinc.com.