Despite spending millions of dollars on hundreds of miles of bikeways, American cities are seeing a big drop in the number of people who pedal their way to work. That's according to the latest American Community Survey (a smaller, more detailed version of the U.S. Census), which found declining bike ridership across most American cities last year.

The drop was most pronounced in bike-friendly Seattle, home of the $12-million-a-mile bike lane. In 2015, 4 percent of Seattleites (16,300 people) biked to work. That rate fell to 3.5 percent (14,600 people) in 2016 and 2.8 percent (12,000 people) last year.

This decrease comes as the city of Seattle is throwing a lot of money at building out its biking network. In 2015, Emerald City voters approved the Move Seattle levy, which raised some $94 million to add 110 miles of bike lanes, greenways, and associated infrastructure. Costs have since increased to a point where Seattle residents may get only about half the miles they were promised.

Bike lane supporters in the city pointed to a number of reasons for the precipitous drop, including drops of precipitation. Both the Seattle Bike Blog and The Seattle Times suggested that the rainy city's unusually wet winter weather and downtown construction help explain the decline in biking.

That may be true, but biking was down in many cities, even those spared harsh winter rains. Take Los Angeles, where biking has been falling for years, even as the city has added bike lanes at a frenzied pace. The city's 2010 Bicycle Plan called for quintupling the number of bike lane miles at a projected cost of $234 million to $437 million. The state and federal governments have chipped in with grants for bike infrastructure. The city has been adding from 30 to 60 lane miles (the number of lanes multiplied by miles of path) of bikeways a year, reaching some 1,200 lane miles—including fully separated lanes, recreational trails, and marked or "sharrowed" lanes—by 2017.

Despite this investment, biking numbers are down. In 2013, some 21,000 Angelenos (1.2 percent of commuters) biked to work. After a spike in 2014, the number of bikers has been falling continuously. Last year, only 17,930 commuters (about 0.9 percent of all commuters) biked to work, according to the new survey data.

Some cities, including car-centric places like Dallas and Phoenix, did see small gains in the share of commuters biking to work, but not enough to reverse the national trend. In the U.S. as a whole, only 0.5 percent of people biked to work in 2017, down from 0.6 percent in 2016.

What is driving this drop is difficult to say. The reasons could vary from city to city. Yet the fact that biking is falling even in those cities most committed to expanding bike ridership suggests that throwing more money at bike-only infrastructure cannot change the fact that most people would rather use non-pedal-powered modes of transportation to get around town.