The City of Seattle has installed new dedicated bike tracks around the city, often converting car travel lanes or on-street parking. An assumption has been that to increase bicycle commuting and biking in general requires a more complete network of dedicated lanes and tracks so that rider feel safe. So, are we gaining riders as the network expands?
Measuring biking is tricky. Census data on bike commuting is poor at the local level, where the American Community Survey sample size does not allow for meaningful localized measures. And even at larger geographic level, we really don’t know how many people who report being bike commuters are doing so every day, or only when weather and daylight permit.
One data source we do have is the bike counters that the City of Seattle has installed on a number of bike tracks and routes around the city. The data is reported on an hourly basis, so we can get a good idea of travel patterns. Unfortunately, there are gaps in the data where the counters have malfunctioned, but in many cases we can get a consistent picture.
First question is whether bike track use is growing over time. The network has been expanding, and the city has signaled its strong support for bike commuting, so we might expect to see growth over time as more origins and destinations get connected. Figures 1 and 2 show bike track use during the month of August—the best biking weather of the year—for 2015 through 2019, and for May or June of 2020.
While we can expect some variation due to weather and the functionality of counters, it does not appear that the city’s bike tracks are experiencing significant steady growth. The Fremont Bridge crossing, the busiest of the counters, did see a surge in 2019. But the Fremont Bridge saw surprisingly little growth in the prior two years, following the opening of the Westlake bike track, which provides a safe route to South Lake Union.
Data for 2020 shows an understandable drop due to the pandemic shutdown and the widespread practice of working from home. The Spokane Street Bridge did not see a drop, but that would be expected given the closure of the high level West Seattle Bridge.
One concern about biking as a reliable commuting mode is the impact of weather and daylight. While many hardy souls put on their rain gear and ride in any weather, others cycle during the nicer weather and use other modes in less nice weather. The lack of daylight during commuting hours in winter can also make biking seem less safe.
Figure 3 shows the seasonality of bike commuting on the Spokane Street Bridge route. It shows average daily rides in all directions by month (left axis), along with the average high temperatures for that month (right axis). February 2019 was unseasonably cold and had a number of days with significant snowfall.
The pattern is quite clear: colder temperatures and low-light months see lower bike commuting. Bike trips on the Spokane St. Bridge in November, arguably the month with the worst weather of the year, were 40 percent below August, the month with the best weather.
Rain also makes a difference. Figure 4 shows the impact of rain on trips on four of the city’s bike routes. On these six weekdays in September, 2019, the temperatures were in the 60s and 70s, but three had rain and three did not.
Now, this is a small sample size, but it does illustrate another impact of weather. On three of the four routes, the heavy rain had a larger impact than light rain, so cyclists are clearly discerning. The day of moderate rain, September 12, also had temperatures near 80 degrees, so maybe the rain was refreshing and did not discourage cycling.
According to the 2019 American Community Survey, between 1.5 and 1.9 percent of King County residents commute by bicycle and between 3.2 and 4.2 percent of Seattle residents cycle to work. These figures are unchanged since 2014, which is consistent with the minimal growth in cycle track use.
Seattle has been investing in bicycle infrastructure for quite a number of years and seems to have little to show for it in terms of bicycling growth. In many cases there is a cost to these investments in the reduction in lane miles for cars. It would be useful for the city to undertake a comprehensive cost-benefit analysis of these investments before engaging in more car lane/bike track tradeoffs.