A Capital Bikeshare user rides in a District bike lane in December 2012. The bike-sharing service and the expansion of bike lanes in D.C. have led to an major increase in cyclists on local roadways. (Andrew Harrer/Bloomberg News)

When a bicyclist and a motorist collide on a D.C. street, assigning blame for the accident can be a murky affair. Maybe the car followed too closely, or maybe the bike swerved — or maybe both.

But a District liability law requires an answer in black or white: For a biker to collect on insurance, the accident must be 100 percent the driver’s fault.

A powerful D.C. Council committee on Monday began weighing a major change to that law that would give bicyclists the right to argue fault in shades of gray with insurance companies and juries. That would give bicyclists a greater chance to recoup a share of medical bills and other costs after a crash.

The council action rustled an entrenched insurance industry that has long succeeded in fighting changes to liability laws in the D.C. region — including in Maryland and Virginia — even as they have been replaced in 46 states.

“If the burden is to explain why bicyclists need to be treated differently,” said Judiciary Committee Chairman Tommy Wells (D-Ward 6), “it’s clear to me that one of the main differences is that generally it is the bicyclist who is taken to the hospital while the motorist makes his case to police.”

The number of reported bike accidents in the District has more than doubled to almost 600 annually over the past six years as the popularity of bike sharing has exploded and lawmakers have rushed to expand bike lanes and promote bike riding as a green alternative to driving. With the increase has come greater animosity on District roadways.

Now, the District has an increasingly powerful counterlobby of bicycle riders, and it is poised to help force a crack in insurance law that has existed in the District since before the dawn of the automobile.

Insurance industry executives on Monday warned of far-reaching consequences if the council proceeds. Most immediately, they testified, car insurance rates in the District could go up. Then, other liability laws that govern how compensatory damages are allocated could face challenges.

“It’s a slippery slope once you have opened the door,” said James Taglieri, a representative of the Trial Lawyers Association.

Bruce Deming, a personal-injury attorney who dubs himself “the Bike Lawyer,” disputed that assertion. “We don’t live in a black-and-white world,” he said. “This is an incredibly harsh doctrine that slams the courtroom door on people who need help.”

Council member David Grosso (I-At large) authored the bill. He said the city’s current standard, known as contributory negligence, is outdated and does not comport with modern notions of fairness, nor take into account the lopsided injuries that result when a bicyclist and a motorist collide.

Under his bill, the District would carve out an exemption to liability law regarding bicycle accidents, requiring insurance carriers to use a model common to most states that compares the relative fault of the two parties and awards claims based on who was more at fault.

If a driver more egregiously erred than a bicyclist, the driver’s insurance company could be required to pay the bicyclist’s claim.

Shane Farthing, head of the Washington Area Bicyclist Association, said part of the problem under the current law is that D.C. police officers lack training and compassion for bicyclists, and that even the slightest remark on a police report suggesting partial fault of a bicycle rider can prevent the bicyclist from ever succeeding in a claim.

Tracy Loh, a bicyclist and pedestrian advocate who was hit from behind by a driver on Connecticut Avenue six years ago, breaking her pelvis and injuring her back, implored Wells’s committee to approve the bill and send it to the full council for a vote.

She also urged that pedestrians be given the same rights.