Counting Bikes to Plan for Bikes

Photo: group of bikes at intersection

There is an old adage that says “you can’t manage what you don’t measure”. Arlington County planners are taking this to heart as they continue their work to make Arlington a great community for biking.

The County has established a robust program of automated bicycle and pedestrian counters, and the acquired data provides a wealth of interesting and useful information. The data strengthen the case for continued investment in and encouragement of bicycle and pedestrian transportation, and help direct efforts where they will have the most impact.

Traditionally, bike trip data has come from a combination of manual counts and surveys. Both methods are labor intensive, prone to inaccuracy, and provide limited insight into the long-term “pulse” of active transportation. Imagine working for weeks to organize a team of volunteers for a count event, inducing them (perhaps with cookie bribes?) to commit to a day of standing and observing on a street corner with a clipboard, and compiling the results, only to be frustrated to find some volunteers did not follow directions carefully, or to have the entire day sabotaged by rain, with numbers much lower than normal, and therefore unrepresentative. There is something to be said for electronic surrogates that work 24-7-365, rain or shine.

Arlington’s first two automated bike and pedestrian counters were installed in the fall and Spring of 2009-10 on the Custis and Four Mile Run Trails. They use a combination of in-ground inductive loops and passive infrared detectors to collect data on trail volumes and travel direction. (Yes, for the curious, the occasional deer might get also be counted as a pedestrian).

As of this writing, in April 2014, the County has 16 permanently installed bicycle and pedestrian counters on shared-use trails, 10 permanent bicycle-only counters in on-street bike lanes, 3 mobile counters typically used for short term sidewalk counts, and our newest device, the first real-time #bikeometer bicycle counter on the east coast. This device, near the intersection of Lee Highway and N Lynn Street in Rosslyn, shows cumulative daily, monthly, and year-to-date totals at one of the busiest bicycle locations in the region. We think the database we are building is not only valuable in the near term for planning and forecasting, but will pay dividends for years to come as a record of active transportation.

early insights derived from the data include:

  • People are riding a lot of bikes on County trails! Most all our major trails see around 500,000 trips per year.
  • People are biking on these trails to commute to and from work, and for recreation and fitness. Some of the trails display a balance of uses – other locations are predominantly used by commuters or recreational riders.
  • Many cyclists are not deterred by winter cold temperatures alone. But rain, snow and ice do have a major deterrent effect on ridership.
  • We enjoy a solid 6-7 month high season of strongest bicycle numbers.

Figure 1: Bike and Ped Trips on the Custis Trail West (Uphill) of Rosslyn

Click image for larger version.

Graph: Bike Trips on Custis Trail, Arlington County

Figure 1 shows the popularity of the Custis Trail, an off-street, paved multi use pathway which runs east-west across Arlington paralleling I-66. Peak months approach 50,000 trips, and pead days can come close to 2,000 bike trips. Imagine if all those trips had been additional vehicle trips on I-66 and other already congested roads. Biking is making a difference! We have seen an average 5% annual increase in bike numbers of the last three complete calendar years.

Figure 2: A.M. and P.M. Commute Hours

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Alternate content: Figure 2 graph data in HTML table

Graph: Custis Trail Peak Hours

Figure 2 shows that the Custis Trail is being used heavily as a commuter route during the week. Notice the am and pm spikes, which are typical commuter travel patterns. Even a casual observer will note most riders with backpacks or panniers during commuting hours. This regular, predictable, dependable activity sends an important message. The Custis is a valuable commuting facility, and much more than a recreational trail. In fact, it’s more popular on weekdays than weekends. The counter data underscores this importance in the inevitable competition for limited funding for transportation improvements, expansion and general maintenance.

Figure 3: Effect of Weather

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Alternate content: Figure 3 graph data in HTML table

Graph: Effect of Weather on Bike Trips

Figure 3 shows the effect of the weather on bike trips. Cyclists on the Custis Trail are much more averse to rain than to cold temperatures. This observation helps strengthen the case for continued trail maintenance and snow clearing throughout the winter. If the trails are clear of snow, many people will ride despite the cold. A relatively small investment in clearing the trails keeps people on their bikes, which means fewer cars on the road.


From an initial two counters in service since 2009-10, Arlington County has built a network that now includes 16 bike and pedestrian counting locations on off-road shared-use paths; 10 bike lane counters; three mobile devices suitable for short term bike and/or pedestrian counts, and the first #bikeometer real time bike counter on the east coast. The wealth of acquired data helps legitimize cycling as a valid form of transportation, and guide the continuing efforts of transportation planners. So the next time your ride in Arlington, remember – we are “counting” on you!

Did You Know?

Adults who bike to work have better weight, blood pressure, and insulin levels.

Gordon-Larsen, P., et al, 2009

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