A Washington cyclist rides parallel to Metro’s Red Line in May 2011. (Linda Davidson/The Washington Post)

Bike commuters break down into two primary camps: those who appear to have no fear, whizzing through traffic on busy roads; and those who stick mostly to quiet side streets and off-road trails because the thought of riding in traffic terrifies them.

Some planners in the Washington region — along with a growing number across the U.S. — are beginning to pay more attention to the vast majority of people who they say would bike more often and to more places if doing so felt safer.

Planners in the District and Montgomery and Arlington counties are using satellite maps and street-level data about road widths, speed limits and parking patterns to gauge the “level of traffic stress” (LTS) along local roads. That stress factors in the sense of danger, as well as unpleasant noise and vehicle exhaust.

An LTS 1 route, such as an off-road trail, feels safe and comfortable for children. One with an LTS 2, such as a wide sidewalk along a busy road, feels fine for most adults classified as “interested but concerned” cyclists. An LTS 3, such as a bike lane on a two-lane road with slower traffic, is tolerable for “enthused and confident” adult riders. An LTS 4? They’re for what planners call the “strong and fearless” cyclists willing to ride, well, almost anywhere.

How safe people feel on a bike is one of the most significant factors in where, and even whether, they’ll ride, experts say. Getting more people to feel comfortable riding more often and more places, they say, will be key if local governments want to reduce traffic, improve air quality and boost public health.

“It’s kind of a new way of thinking that’s more intuitive,” said Darren Buck, bike program specialist for the District Department of Transportation, which released its first traffic stress map earlier this month. “Instead of analyzing formulas, it identifies the dealbreakers on a street, where people say, ‘If there’s no signal to cross this busy road, I’m not going to bike on it, no matter what.’”

Most striking, planners say, is the fact that urban areas and even many parts of the sprawling suburbs have plenty of residential streets, side roads and trails that feel comfortable enough for children and most adults. Montgomery planners say they found that 70 percent of the suburban county’s roads meet that criteria.

The problem: Areas that offer comfortable rides are often cut off from one another by high-stress roads that don’t have a convenient, safe crossing. That leaves what planners call islands of safe cycling routes, which often don’t lead anywhere and make biking to school, work or the store unrealistic for most children and adults.

“Every city with a bike map has said, ‘Here are ways to get from one place to another by bike,’ ” said Peter Furth, a Northeastern University engineering professor who devised the LTS criteria based on Dutch standards as part of a 2012 study. “But we knew these were places people didn’t want to ride.”

Local governments would never map out a road or transit network with stretches that most drivers or transit passengers didn’t feel safe enough to use, Furth said.

Planners say the LTS rankings are helping them find the daunting streets that, with a new bike lane or crosswalk, would connect larger areas of safe-feeling routes. In the District, Buck said, the map showed inhospitable roads connecting neighborhoods to downtown. Montgomery planners said they’re paying particular attention to stressful roads between neighborhoods and nearby schools, recreation centers and transit stations, including Metro stations and those planned for the future light-rail Purple Line.

Providing comfortable connections appears to be particularly important in attracting more women and older riders, planners say.

Montgomery planner David Anspacher said the new mapping tool has changed how the county analyzes the effectiveness of its bike network. The public also can use the online map to see the stress levels along different routes.

“Before, we’d draw lines on a map, but we didn’t have much data to back them up,” Anspacher said. “Now we have the data to prioritize investments and ultimately encourage more people to bicycle by making it an attractive option for them. . . . With a few strategic investments, you can really open up the network and start connecting those islands.”

Arlington planners say their recently collected stress data is helping them prioritize new biking infrastructure and links that need to be built from residential areas to job centers, schools and other cycling destinations. The data isn’t publicly available, but the county offers an online Bicycle Comfort Level Map that marks the safest and most comfortable streets based on input from residents and cyclists.

In examining traffic stress levels in San Jose, the 2012 study that Furth co-authored determined that relatively small but strategic projects — providing a short connection in a path or making an intersection crosswalk safer — could make a big difference. Making such improvements to 32 miles of roads in San Jose, the study found, would almost triple the percentage of that city’s home-to-work trips that would be fully connected at low-stress levels.

Colin Browne, spokesman for the Washington Area Bicyclist Association, praised local governments for focusing on riders’ comfort levels. He said he hopes planners can fine-tune the map data to better reveal areas that appear to be low-stress but aren’t, such as bike lanes along L and M streets NW that still require cyclists to dodge vehicles. Crossing Massachusetts Avenue in the bike lane on 15th Street NW also is scary, he said, even though it has a traffic light.

“It’s a much higher-stress experience,” Browne said of crossing the avenue, “than riding in the lane itself.”