How often is that bike lane blocked? A crowdsourced tool takes a look.

It’s a common conversation topic among bike commuters: drivers block bike lanes all too often, and cities rarely seem responsive about it. This has been anecdotal for some time, but advocates in the Washington, D.C., region have been collecting some useful data and in order to develop a stronger case for better enforcement and safer streets.

For example, an analysis of D.C. enforcement from the Washington Area Bicyclist Association found that “bike lane parking enforcement is perfunctory at best,” a situation that creates real safety issues for bicyclists and lessens the usefulness of biking infrastructure.

Across the Potomac in Arlington County, where this information is similarly difficult to find and quantify, biking advocate Chris Slatt built his own crowdsourcing site, “Parking,” to generate data where there was none. Slatt’s site asks users to check provided traffic cameras screenshots for infractions, with the goal of determining just how safe the lanes are for bicyclists and how often they are blocked.

Addressing a system problem

For drivers, momentarily blocking a bike lane may seem like a non-issue. But in practice, bicyclists encountering a parked car face the dangerous proposition of suddenly merging left into fast-moving traffic. Frequently blocked lanes create a stressful biking environment, which ultimately deters riders.

clarendon blvd evening

A sample screenshot from the site, pulled from a traffic camera. Note the car and FedEx truck blocking the lane.

Slatt, a member of Arlington’s Bicycle Advisory Committee and chair of WABA’s Action Committee for Arlington County, understood the challenge of documenting blocked lanes, and reached out to the area’s bicycling community tackle the task.

BAC members provided feedback on the most troublesome areas, from which Slatt chose the most-mentioned blocks, eventually looking into Arlington’s public traffic camera feeds to determine which ones have a reasonable view of the bike lanes in question. Relying on two cameras, one on Clarendon Boulevard at Wayne Street and one mid-block on Crystal Drive, the Parking Dirty site pulled one screenshot per minute for three 24-hour periods in September and October of last year.

The system then relied on participants to evaluate the screenshots, using majority rule to determine a photo’s status – at least two users must on whether or not a lane is blocked. Since he began promoting it, about 160 people have helped to build the tool’s dataset, which has revealed regularly blocked bike lanes. One block of Clarendon Boulevard was blocked from 25 to 47 percent of the time, depending on the day in question, and Crystal Drive’s bike lane was consistently above 60 percent.

Quantifying these obstructions does support bicyclists’ sense that this is a chronic issue. But there can still be a disconnect between concerns among cyclists and the police’s understanding of the issue. For example, one BAC member has brought up bike lane obstruction in the past with their police liaison, which the officer challenged by responding: if nobody is biking in a blocked lane, is it really blocked?

In practice, this means that the enforcement policy requires concerned citizens to report a blocked lane, at which point an officer is sent to fix it.

“That works if it’s an uncommon problem,” Slatt says. “But a systematic problem needs proactive enforcement. When the chances are greater than 50 percent that a lane is blocked … if it’s more likely than not the bike lane is obstructed,” then the call-to-report system doesn’t make sense, and proactive ticketing does.

parkingdirty-cc drive

Results from a September day on Crystal Drive. Source:

Informational barriers

Parking Dirty addresses part of a multifaceted campaign to improve bike safety in Arlington, part of which involves solving technological barriers to data collection.

For example, while it’s relatively simple for one to obtain D.C. traffic citation records, Slatt found barriers to doing so in Arlington. Slatt filed a Freedom of Information Act request with the county to view tickets police have written for blocking bike lanes. Unfortunately, only summary data is digitized, and anything related to drivers endangering cyclists is filed as “other.” Getting numbers on these citations would require digging through paper records.

While the numbers from Parking Dirty go a long way in articulating a common issue cyclists face, more complete information on how the police enforce road safety would provide a fuller picture that could better focus the conversation.

Towards safer lanes

Despite the barriers, Slatt believes Parking Dirty’s dataset is enough to kickstart a discussion toward more proactive enforcement of street safety, especially for people on bikes. He also explains that it’s important to remember that “this data is just for one or two blocks. But if one is blocked 30 percent of the time, and so are the two blocks before and after, it adds up quickly.”

Parking Dirty drives this point home by providing a data-based window into how biking feels for cyclists. At the very least, the information that Parking Dirty has collected creates a starting point to better examine and work with community members in a deeper push to create a bike-friendly, multimodal community.

Photo: Top, a sign at the beginning of the protected bike lane on South Hayes Street, in Crystal City, Arlington (Elvert Barnes, Flickr, Creative Commons).

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