Since 2007, New York City has added 31 miles of protected bike lanes — that is, lanes protected by a physical barrier, such as a row of parked cars or a curb. The main point of building protected lanes was to make biking in the city safer. But when the NYC Department of Transportation recently studied the impact of the lanes, they found a secondary benefit: on several different avenues in Manhattan, the lanes actually helped speed up car traffic. The new report, spotted by Eric Jaffe at CityLab, found that on Columbus and 8th avenues, the time it took a car to traverse a specific distance dropped significantly after the installation of the lanes, while on 1st Avenue, it increased only slightly. At the same time, rates of bicyclist injuries declined steeply on all three streets, along with Broadway, 8th, and 9th avenues. So how did the bike lanes speed up traffic? It seems that two factors were important. One is that, for the most part, driving lanes weren't actually eliminated when they bike lanes were built — they were simply narrowed. Additionally, the design of the bike lanes included a dedicated left-turn lane at most intersections, allowing cars to wait to turn left without holding up traffic.