Roundabouts, or roundabouts as they’re sometimes called, are more complex than intersections. A roundabout is a “peripheral straight” intersection, like the intersection of Bank Street in Portland, Ore., where traffic is funneled onto Bank Street Road instead of going straight across the two-lane street and trying to merge with other traffic. That’s just a typical intersection. A roundabout interchanges a two-lane road with a third-lane parallel with only the main road and your right-hand lane. It’s much slower than a traditional intersection, but it’s much easier to drive on the left lane. The left lane is reserved for the right-hand lane and then for the left-hand lane. Drivers with cars on both the left and right lanes can still switch lanes. But if there’s congestion on the left lane, you’re stuck. Roundabouts are more complex and can be confusing for drivers when they first get introduced to them. Because they can have traffic volumes of up to 30,000 cars per hour, roundabouts can be highly congested and that can lead to accidents. There’s also a dramatic effect on air pollution. At New York City’s Mets-St. Louis Cardinals game on Aug. 4, 2015, city officials released the results of the carbon emissions from the park-to-court miles and a roundabout ended up contributing the most. Nearly 21,000 cars drove on that stretch of highway in just one hour, which accounts for 4,364 metric tons of greenhouse gases — about 14 percent of the park-to-court miles in the city.