NYC DOT is studying how to speed buses across the car-clogged Queensboro Bridge, and data the agency collected over the summer [PDF] show just how great the need is. Buses are crawling and riders are fed up. Relieving the bottleneck for riders could make transit a far more attractive option for Queens residents. One potential solution — adding dedicated bus lanes to the bridge and its approaches — is a PlaNYC promise waiting to be fulfilled.

Currently, 16,000 New Yorkers ride buses across the Queensboro every day, according to DOT, split about evenly between local and express buses. During the afternoon rush hour, that’s one bus every 30 seconds or so.

And the p.m. rush is also when bus speeds across the bridge slow to the pace of a tortoise. One express bus route across the bridge travels at an average of 12.2 miles per hour between 5:00 and 6:00 p.m., DOT data showed. An hour later in the day, those buses can travel at up to 21.2 mph. Heading through Queens Plaza between 4:00 and 5:00 p.m., express buses crawl along at an average of 4.3 miles per hour — about the same speed as walking.

That Queensboro Bridge buses get snarled in traffic is no surprise. It’s the only free crossing between Queens and Manhattan. Thanks to the Assembly’s refusal to pass congestion pricing 2008, toll-shopping drivers from across the borough and Long Island still funnel into this one point. In 2007, motorists made around 85,000 car and motorcycle trips across the bridge per day in each direction, by far the most auto traffic on any of DOT’s four East River bridges [PDF].

The result is unhappy commuters and presumably fewer bus riders. DOT surveyed riders on Queensboro Bridge bus routes and found that overwhelming majorities saw traffic congestion slowing their commute. The riders estimated that traffic added between five and 15 extra minutes to their trips. Shaving 15 minutes off bus rides could lure a lot more people out of cars and onto transit.

DOT will present its recommendations for improving bus service across the Queensboro in November, but one solution jumps out: bus lanes on the bridge and its approaches to let transit riders zip past stopped traffic. Across town, the Lincoln Tunnel’s Exclusive Bus Lane is a smash success. In the 3.75 hours it’s open each morning, it carries 62,000 passengers into Midtown, saving each of them 15-20 minutes over drivers in other lanes. It’s now so heavily-used that the Port Authority is looking into the addition of a second priority lane for buses.

Bus lanes also have the endorsement of bus riders. Both local and express bus riders suggested dedicated lanes as the way to speed their trip in DOT’s survey.

Installing Queensboro bus lanes would help make good on a still-unfulfilled promise in PlaNYC. Though the city committed to creating bus or High Occupancy Vehicle lanes across the Queensboro, Manhattan and Williamsburg Bridges by the end of 2009, currently there are only HOV lanes on the Manhattan and Queensboro Bridges during the morning peak.