A statistical analysis of biking on the Fremont Bridge, Part 4: Are more people biking?

EDITOR’S NOTE: This is the final post in a four-part series of posts this week by statistician Mike Logsdon. Mike bikes across the Fremont Bridge every day, and put together this analysis of the bike counter data “mostly for the amusement of friends and coworkers.”

Are More Seattleites Bicycling Across the Fremont Bridge? The short answer: Probably.

It’s tough to make any emphatic declarations from 18 months worth of recorded trips, as we have to investigate trends net of seasonal and weather effects. Once again we consider residual ridership — the difference between observed crossings and the number expected given season and weather. Time trends in Fremont Bridge bicycle crossings should manifest themselves as time trends in the residual trips. If daily crossings are growing, then the expected counts will exceed the observed counts at the beginning of the monitoring and reverse at the end of monitoring. If there is no time trend in bicycle crossings, then the residual trips should simply scatter around zero with no pattern.

Figure 6 shows the residual trips, plotted against date. A slight time trend revealed itself, to the tune of a 140 rider per day per year increase. This estimate, however, is extremely imprecise. Any time trend in ridership is simply small compared to the day-to-day variability in bicycle trips, given the duration of the observations.

Fremont_Bike-grow1

Recap

Winter workdays saw on average 2,000 daily crossings. Summer workdays saw on average 4,000 daily crossings. Peak commute times were 8 a.m. to 9 a.m., and 5 p.m. to 6 p.m., with hourly total crossings peaking between 600 and 800 on the nicest days. Seattleites talk a mean game, but left their bicycles parked on the rainiest days. Cascade Bicycle Club Bike Month energized commuters early, but many participants lost interest by the end of the month. Bicycle crossings have probably been increasing by somewhere in the zip code of 100-200 additional riders per day per year, but it’s hard to know for sure due to the large variability in daily commute crossings relative to the duration of the observations.

About Mike Logsdon

Mike Logsdon works as a statistician for Ecotope, Inc. He bicycles twice daily across the Fremont Bridge, rain or shine.
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11 Responses to A statistical analysis of biking on the Fremont Bridge, Part 4: Are more people biking?

  1. Virchow says:

    Really cool fun analysis! thanks for donating your time and expertise Mike!

  2. Dave says:

    Thanks for the great analysis.

    Wondering if you can account for the slight increase in bike trips with the reported increase in Seattle population – that is, the % of bike commuters is actually pretty static?

    • Mike Logsdon says:

      That’s definitely a possibility. Unfortunately, just looking at counts of crossings doesn’t provide the information to break apart time trends into behavioral changes of the people already here and the addition of new people.

  3. Gary says:

    With 200 more riders per day, if they are like me, starting out not riding everyday, we could have 400 more people riding.

  4. Wells says:

    “Are More Seattlers bicycling across Fremont Bridge? Short answer, probably.”
    Oh, so, impressed, oh yes, oh, yes, YES.
    Wait, I forget, where in Seattle is bicycling NOT SUCKY?
    Yee gods. Downtown/inner Seattle is a mess of dangerous stinky traffic.
    Trolleybus is ideal but neglected repeatedly over the years.
    “Let’s not fix those dang electric buses. Best riders always paying,”
    said the boys from Boeing, Olympia, Hanford. “Aluminum will do the job.”
    Gallopping Gerty, meet Bertha Wormbedding.
    Bertha is looking for employment elsewhere.
    Metro is no better than Wsdot or Crunican’s Sdot.
    Sound Transit grandiose parking garage transit centers,
    whoop-dee-frickin-doo. Just lovely. Diesel buses idling.
    Yeah, Transit Centers, a realishly smart place to put concrete somewheres.
    With, like, buses.

  5. Karl says:

    “Seattleites talk a mean game, but left their bicycles parked on the rainiest days.”

    That’s a little harsh, and not strictly correct. The way that is worded sounds like no one in Seattle cycles on the rainiest of days. As someone who doesn’t own a car (and detests taking the bus) I can assure you I cycle commute to work every day and see others out there doing the same. In fact, unless I’m mistaken, your data backs this up. Are there a lot of fair whether cyclists out there? Sure. Do all cyclists stop riding because it is raining? Hell no!

    Also, I realize you were doing this on your own time, but I think you dropped a very important variable by not using the UW weather data. I’ll ride in any amount of rain, but the only thing that will put me on the bus other than an injury is high winds. I strongly suspect I am not alone in this. Any day with winds of 35 mph+ probably sees a very significant drop in cyclists.

    • Mike Logsdon says:

      It’s true that could have been phrased better. The line was meant to refer to the large decrease in bicycle traffic on wet days, but yes there are always some bicycle commuters no matter the rain (myself included).

      I would also be pretty curious about the effect of wind. I don’t think it would change any of the conclusions of this series, although it would probably increase the precision of the time trend estimate (by lowering the variation in the residual trips), and in itself offer an interpretable regression coefficient, much like with rain.

      • Keith says:

        “I would also be pretty curious about the effect of wind”

        Well, as a commuter between West Seattle and Bellevue, taking a single sample of Thursday this week ( 2 days ago), riding home over the bridges the number of riders dropped significantly compared to the average day. However of course the weather forecast also call for PM rain, so as usual my sample might be not isolated to wind. It never rained, but the wind caused me to slow down significantly on the ride of the I90 bridges.

      • Gary says:

        Wind, unless it’s a hurricane level is not a factor for me. I kinda enjoy the wild ride over the bridge when it really blows.

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  7. Great analysis. I wish there were more bike counter data sets available so that this analysis could be done across multiple cities.

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