LOS ANGELES – On Thursdays, Charles Dandino becomes the conductor of an unusual kind of train.

He leads what he calls a "bike train," a group of cycling co-workers who band together for their 6-mile ride to work in the name of safety, as well as for fun and exercise.

Around the country, city transportation officials wish there were more bicyclists like Dandino as they seek to cut traffic congestion, promote health and identify alternatives to cars. After rising for several years, the percentage of commuters turning to bikes declined for the third year straight, U.S. Census Bureau figures show.

Nationally, the percentage of people who say they use a bike to get to work fell by 3.2 percent from 2016 to 2017, to an average of 836,569 commuters, according to the bureau's latest American Community Survey, which regularly asks a group of Americans about their habits. That's down from a high of 904,463 in 2014, when it peaked after four straight years of increases.

In some cities, the decline was far more drastic. In Tampa, Florida, and Cleveland, cycling to work dropped by at least 50 percent, although in some cities, cycling to work was up just as dramatically.

Experts offered several explanations for the nationwide decrease that has unfolded even as cities spent millions trying to become more bike-friendly.

Most obviously, lower gasoline prices and a stronger economy contributed to strong auto sales and less interest in cheaper alternatives, such as mass transit and bikes. The rise of ride-hailing services such as Uber and Lyft and electric scooters cut into bike commuting, said Dave Snyder, executive director of the California Bicycle Coalition.

Another bike advocacy group, the League of American Bicyclists, found a mix when it examined biking trends in the 70 largest cities based on its own analysis of Census data. Bike commuting was up slightly from 2016 to 2017 in one of the large cities where it is most popular – Portland, Oregon. There, 6.3 percent of commuters bike to work. It was also up in the second and third most popular big biking cities, Washington and Minneapolis.

It was down 19.9 percent in fourth-place San Francisco, 11.4 percent in fifth-place New Orleans and 20.5 percent in sixth-place Seattle over the same one-year time period.

"It shows that while we have made investments over the last 20 years" in bicycle infrastructure, "we are still far from having safe and connected networks that make people feel safe biking to work," said Ken McLeod, the league's policy director.

Federal highway spending on bike- and pedestrian-related improvements totaled $915.8 million this year.

"This level of spending is relatively small given the needs for bicycle and pedestrian infrastructure," McLeod said.

City officials around the country said they try to support bike commuters. Besides new bike lanes and trails, many cities added bike sharing programs, which give cyclists the ability to rent a bike to ride point-to-point or for the day.

Besides the one-year drop in Seattle, the city saw a 19 percent drop-off from 2011 to 2017, according to the league's report. Dawn Schellenberg, spokeswoman for the city Department of Transportation, said that may be due to the city's famously rainy weather or commuters using bikes for only part of their trips, using them to connect to public transit.

In Austin, Texas, there was a 24.1 percent drop in bike commuters from 2016 to 2017 and a 38 percent decline from 2011 to 2017. City officials said they have a strategy to increase ridership by concentrating their biking infrastructure efforts on trips up to 3 miles that are "very doable by bike," said Laura Dierenfield, the city's division manager of active transportation.

"We want to to make it possible for people to have a variety of choices about how they get around," she said.

Long Beach, California, saw a 23.1 percent increase in the number of bike commuters from 2016 to 2017, though it was down 19 percent from 2011 to 2017, the league's report says. Over the past decade, Long Beach added bike lanes throughout the city and dedicated routes separated from traffic, including some that recently opened. Its bike-sharing program continues to grow, having 11,000 members.

"I think we are getting a lot of commuters coming into the downtown," Public Works Director Craig Beck said. "A separated bike lane that goes four blocks doesn't really do anything. It's about point-to-point safety."

For bike commuters, safety is a top consideration.

In a push to make the city more bike-friendly, Los Angeles started installing miles of protected bike lanes and embracing "road diets," or slowing streets to make them safer for bikers and pedestrians. In a city where the car is king, a backlash from motorists drastically cut back those efforts.

As a result, Bicycling magazine named Los Angeles the worst biking city in America in October.

"The City Council and the mayor's office are only listening to angry drivers who don't want their commute to be slowed down by anyone," said Ted Rogers, a veteran bike rider who writes the BikingInLA blog.

"I hear from countless people who say they quit" biking, he said. "They just don't feel safe on the streets anymore."

Safety was one of the reasons that Dandino, 31, said he created his bicycle train six years ago. He started by recruiting co-workers to meet early at a coffee shop in the old business section of Pasadena, California, to ride together to work at NASA's Jet Propulsion Laboratory.

A bike devotee, Dandino said it was tough at first to find volunteers. He said he now will have about eight riders on a typical day, the numbers swelling to as many as 15 when there are more interns.

"Riding bikes in a group is more thrilling and a joy to do," said Dandino, a mechanical engineer. "On the safety side, it makes us much more visible, and there's strength in numbers."

As the self-described conductor, Dandino said he makes the group keep together and is ready to fix flats or help with other bike repairs if a rider needs it.

Barbara Insua used to ride regularly with Dandino's bike train. She said she loved getting a workout on the way to her job as a graphics designer. "Uphill to work. Downhill home," she said. Then she bought a new car and stopped riding.

As her 50th birthday looms, she said she's inspired to join the train again.

"I am going into a phase in which I want to come back to biking," Insua said. "There are so many wonderful things about biking."