Uses vs. Users
One of the most important points to note about the count data is that it shows number of uses or trips, not numbers of users or numbers of total visitors. Trail users will be counted every time they pass the counter, meaning that a trail user who takes an “out and back” route will be counted twice. All of the trail sections counted likely have a high percentage of these types of users, but it is difficult to calculate the percentage to be used in corrections. The published data from the Census therefore represents the number of trail trips or uses not trail users.
There are some limitations to passive infrared counter technology. First, the counters are not capable of determining the type of use so pedestrians, bicyclists, and any other user are indistinguishable in the count data. Second, there are multiple conditions that can result in error in the data including undercounting due to things like multiple people passing the heat sensor at the same time, undercounting due to traveling side by side, bikes passing the counter too fast, mechanical error, or technical failure.
In order to account for the potential differences between the actual number of trail uses and what IR counters register, an adjustment factor is used to correct the raw counts for each trail. Adjustment factors are determined by multiple hours of manual counts. To complete a manual count, a volunteer is situated within view of the IR counter and records the actual number of people who pass by the counter. The manual counts are compared to the number that is recorded on the counter for that same hour to determine the adjustment factor.
Short Term vs Long Term Counters
The Trail Census Dashboard displays data from counters installed "long term" (one year or more - many continuously since 2017!) as well as "short term" (weeks to months). Counters installed long term require regular monitoring from local volunteers, and at least four visits per year by CT Trail Census staff to download data and for regular maintenance. With so many counters spread over the entire state, getting to all counters during just one round of visits can take several days of staff time, and hundreds of miles of travel.
With a limited number of counters, and a lot of demand for local trail use data, CT Trail Census staff use short term counts to help local trail managers better understand use on their trails. These counts are conducted over at least several weeks to provide a good representation of hourly and daily use patterns, and comparison to similar nearby trails can allow for estimates of annual trail use.