The Alexandria City Council voted unanimously Saturday to create bike lanes on one of the city’s busiest thoroughfares after an intense debate over a plan that will scrap parking spots on King Street west of Old Town to make way for the cycling route.

In a region where bike lanes seem to appear as suddenly as spring crocuses and with as little controversy, many residents of Alexandria strongly objected to a plan that will remove more than two dozen parking spots to create lanes on a span of King Street from Janneys Lane to West Cedar Street.

Advocates argued that not only are more people using bikes for commuting, but creating the proper infrastructure for them is also the key to the future economic health of cities like Alexandria. Opponents said they are not anti-cycling, but many live more suburban lifestyles which require cars for hauling children and large loads of groceries or traveling to non-transit-friendly areas for work. Those who walk warned that bike lanes will not provide better protection from motorized vehicles. City officials disagreed.

Ultimately, the Council approved the plan recommended by city transportation chief Rich Baier.

“We are trying to achieve a dramatic change in behavior, and that must be accompanied by an attitude change,” Baier said. “What makes this especially difficult makes it an especially important decision.”

King Street in Old Town is a narrow, tourist-oriented street of small shops and offices that is typically clogged with slow-moving traffic. But once westbound travelers reach the Metro station, they move under a railroad viaduct and turn uphill. The street becomes predominantly residential past the George Washington Masonic National Memorial, and drivers tend to accelerate well beyond the 25-mph speed limit, even as bicyclists struggle with a 5 percent grade and walkers are separated by nothing more than a curb from speeding vehicles.

The street is only 30 feet wide, with each lane assigned 12 feet and the remaining space relegated to parking. Baier and his staff originally planned to re-stripe the street, narrowing the traffic lanes to 10 feet and using the remaining space for bike lanes most of the way to Janneys Lane, where King Street widens into a four-lane street on its way to its intersection with Interstate 395.

But residents responded to Baier’s plan, announced in December, with outrage — and not only because they would lose parking spaces. They stopped the plan temporarily.

“We just don’t feel it’s safe,” said Lisa Beyer Scanlon, a neighborhood resident who said creating bikes lanes on King Street would be like “double-black-diamond” ski slopes. “I don’t know why we act surprised when people speed. There’s nothing there to tell them not to speed, except their conscience.”

All sides agree the main issue is safety for bicyclists and pedestrians. City traffic studies show that 85 percent of the vehicles exceed the speed limit, averaging 33 to 35 mph. Residents say that emergency vehicles, commercial trucks and school buses routinely sideswipe cars parked on the street.

Baier returned with a revised proposal, approved Saturday, that would remove 27 parking spaces. Bicyclists would share the traffic lanes with motorized vehicles in the areas where parking is still allowed. He also said the city would install new crosswalks, some with rapidly flashing beacons; pedestrian countdown signals at one intersection; and an electronic speed indicator that lets drivers know how fast they’re going. Narrowing the lanes to 10 feet reduces typical vehicle speed by about 41 / 2 mph, national transportation studies show.

Bicycle-lane proponents, as well as the city’s police, fire and bus company representatives, supported Baier’s proposal, calling it scientifically and professionally well-based, but many area residents remained opposed.

Currently, only about 12 bicyclists use the street at peak hours, city surveys show. Advocates said that bike lanes will encourage more to ride on the street, and that would help slow traffic because drivers will become more aware that they are on a residential street.

Opponents collected signatures of 400 neighborhood residents who opposed the city’s proposal, and they suggested that more traffic enforcement and more on-street parking, not less, would create a safer environment.