Aamer Madhani

USA TODAY

CHICAGO — The problem for cyclist Gillian Wu started when she yelled at a gaggle of pedestrians lingering in the bike lane to get out of the way.

The group, which included a woman carrying a small child, responded with jeers. Wu, 21, a heavy user of this city's extensive bike lane system, said she decided to stop anyway, hoping she could engage the group constructively.

Instead, one man in the group told her he hoped she'd get splattered by a semi, called her entitled and concluded "the world would be a better place without me and people like me," according to Wu.

"I think there are a lot of people who can relate to that aggression," said Wu, who first vented about the incident in an open letter on Craigslist this month. "I think there are also a lot of people who can relate to the way I felt. But there have got to be more productive ways to have this conversation."

Wu's letter went viral and spurred a spirited — and sometimes vitriolic — debate in which some motorists berated cyclists as thoughtless, spandex-clad elitists who pay no heed to traffic laws, while bikers noted that motorists are responsible for thousands of deaths and hundreds of thousands of injuries annually as a result of unsafe driving.

Over the past decade, "bike lane backlash" has been commonplace as communities big and small have established thousands of miles of dedicated cycling lanes throughout the country. Local governments consider bike lanes with nearly all long-term road projects.

On social media, the debate is escalating as rhetoric and fervor match the passion shown on controversial issues such as gun rights and the Middle East peace process.

The rage may have hit a peak last week after a prominent Washington Post columnist suggested some motorists might think it worth paying a fine to hit bicyclists.

That column came days after National Public Radio host Scott Simon faced public scorn from cyclists after he wrote on Twitter, "Any walk through downtown demonstrates cyclists think they are above the law. Does that explain Lance Armstrong?" Seemingly chastened, Simon later wrote on his feed that he learned many cyclists feel threatened by cars.

The issue has become an emotional one for Americans as drivers are increasingly told they'll have to share the road with bike riders, an adaptation that has been easier said than done for a car-obsessed country.

Biking has boomed in recent years as cities have gone on a "road diet" to reduce congestion, cut air pollution and improve quality of life. It still represents a tiny fraction of how Americans get around in the country's largest cities.

Anti-biking sentiment is unique in how it crosses political and racial lines like few other issues in the public square. Opponents often argue that cities pushing for bike lanes pour precious tax revenue into catering to Millennials and high-income professionals that cities see as crucial to keeping urban centers vibrant. That resentment is echoed in working-class and low-income areas.

Most perplexing is how the tensions over America's roadways show no signs of dissipating even as cycling on dedicated bike lanes has increasingly become an option for Americans, particularly those in and around urban centers.

The number of Americans traveling to work by bike spiked by 60% from 2000 to 2012, according to U.S. Census Bureau statistics. In the USA's 50 largest cities, bike commuting accounts for 1% of work travel. Cycling advocates point to polls that show Americans overwhelmingly support establishing bike lanes in their communities and are more likely to cycle when lanes are established.

But when officials push to create dedicated bike lanes, they routinely face stiff resistance.

In Louisville, which has established about 40 miles of bike lanes over the past year, the lanes have ignited an intense debate between motorists and bicyclists about rights and responsibilities, access and public funding.

Last month, the City Council put a temporary stop on funding new bike lanes until Mayor Greg Fischer's staff provides a report on bike network plans. Council members called on the mayor to report on the potential for taxing bicyclists through licensing fees.

Chicago Mayor Rahm Emanuel is getting close to reaching the goal he set in 2011 of establishing 100 miles of protected bike lanes — lanes shielded by poles and other barriers. Emanuel has made the case that bike lanes are a critical tool to creating a quality of life in Chicago that attracts businesses and families.

There is growing opposition from business owners and residents in the northwest corner of the city over a plan to establish protected bike lanes in that area. One option under consideration would reduce four traffic lanes down to two for motorists on a busy 2-mile stretch of road.

Businesses — and a Chicago police lieutenant running for City Council — launched a petition drive opposing the bike lane expansion and in a matter of days were able to gather 4,000 signatures from area residents.

"We've had six cyclists (ride) by in the last hour," said John Garrido, the Chicago police officer who helped coordinate the petition drive against the bike lanes while off-duty. "Really? You are going to reduce lanes of traffic and create more congestion for a few bikes?"

David Wians, who heads the neighborhood Chamber of Commerce, remarked that collecting signatures was easier than he expected. Older residents, many of whom railed at a recent community meeting about bicyclists who roll through stop signs and disregard red lights, led the charge.

"A couple of my clients came in here and saw the petitions," said Wians, an insurance agent. "They went to bingo that night and came back the next day with eight pages of signatures."

In Indianapolis, Mayor Greg Ballard's goal of establishing 200 miles of trails and bike lanes has come under fire from motorists who prefer their roads bike-free and from council members who argue the money would be better spent fixing the city's crumbling infrastructure.

"The bicycle lanes can't be a high priority when you're a billion dollars underfunded for streets and sidewalks," said Indianapolis City Council member Vernon Brown, according to The Indianapolis Star.

The war between bicyclists and drivers has even worked its way into pop culture. IFC's hit comedy series Portlandia has poked fun at the long-running tensions between cyclists and motorists in Portland, Ore. — which leads the nation with 6.1% of work commutes by bike — with a sketch featuring a character who yammers about "bicycle rights" as he rides through the city.

The debate may have hit a new level of absurdity last week in the nation's capital, which has carved out about 72 miles of bike lanes, after Washington Post columnist Courtland Milloy derided bike riders as bullies who are discourteous to drivers and pedestrians.

Milloy's column spurred a protest on the newspaper's headquarters by angry cyclists who took particular exception to a provocative line in Milloy's column: "It's a $500 fine for a motorist to hit a bicyclist in the District, but some behaviors are so egregious that some drivers might think it's worth paying the fine," Milloy wrote.

Robert Schneider, an assistant professor at the University of Wisconsin-Milwaukee's school of architecture and urban planning, suggested that the strife between cyclists, motorists and pedestrians over roadways is the predictable outcome of bicycling emerging over the past decade as a practical mode of transportation for more than just a fringe population.

When there is change in how any public space is being used, there is inevitably going to be tension as different interests compete for finite space, he said.

A study of five U.S. cities with extensive bike lane infrastructure published last month by Portland State University showed that 60% of respondents who lived near areas where bike lanes had been established said the changes in their neighborhood were positive for bicycling. Thirty-six percent said changes have been positive for walking, and 50% said changes in their neighborhood as a place for driving were negative as a result of the bike lanes.

"The most productive and helpful thing communities need to do … is to think of our roadways as places where we all have a shared responsibility to be safe and to behave according to the laws," said Schneider, who has consulted for several cities on bike lane projects. "In the long run, places with a good mix of transportation have shown to be safer than places that are just car-oriented."

Shane Farthing, the executive director of the Washington Area Bicyclist Association, said one problem the cycling community struggles to overcome is the perception that bike lanes are established by cities catering to Millennials and high-income whites.

U.S. Census data show cycling to work is more popular with Americans in lower-income households than it is with the wealthy. A larger percentage of Hispanics and multiracial Americans bike to work than do whites and African-Americans, according to the data.

"In some cases, a bike has become a symbol for some folks of so many social, historical, racial, demographic and mobility issues that have been packed over so much time and space," Farthing said. "At that point, the debate is not about bikes anymore."