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Data can be collected in many ways. In our NPS example the visitors are generally counted by car, not individually, unless it is easy to do. Some visitor's centers have electronic laser beam counters on the door. Others have a simple "clicker" behind the counter that the Park employees trigger each time someone enters. For the purposes of our work here though, let's look at how NPS instructs its employees to count vehicles and estimate visits from traffic counts. Vehicles can be cars, water vessels, motorcycles, horses or bikes. These "vehicle" counts are combined with person per vehicle multipliers. Considerations include:

•Manual counting… visitor centers, historic homes, monuments & memorials

•Mathematical relationships

–Estimate number of visitors in one area based on visitor counts in another area – good for remote places or areas that are difficult to count

•Automated counters on travel corridors

–Traffic counters

–Trail counters

–Door counters

​It is important to only count visitors once so counters must pay attention to those that come in and out more than once if possible. 

As an example, the reported count for Mesa Verde National Park, a standard park, in July of 2014 was totaled in this way:

•Single main entrance to park by road

•Some visitors will be missed by traffic counter

–Bicycles are the most likely visitors that are missed

•Use traffic count as the ‘base’ for estimating recreation visits

•Non-recreation vehicles, buses and bus passengers are counted by hand at the entrance station

•Raw Traffic Count at Main Entrance

–31,063 vehicles

•Reduce traffic count for non-reportable park vehicles (1,500 traffic counter crossings per month)

–31,063 – 1,500 = 29,563 vehicles

•Reduce traffic count for non-recreation vehicles (commuters, inholders, etc.) (575)

–29,563 – 575 = 28,988 vehicles

•Reduce traffic count by number of buses (161)

–28,988 – 161 = 28,827

•There were 28,827 private passenger vehicles at Mesa Verde in July 2014

•Add 10% for those who entered park but were not detected by the traffic counter (this is ‘expanding’ the traffic count)

–28,827 * 1.1 = 31,709.7

•Covert expanded traffic count to visit count

–Use multiplier of 3.2 persons-per-vehicle

–31,709.7 * 3.2 = 101,471 recreation visits by passenger vehicle

•Add in bus passengers (2,115)

–101,471 + 2,115 =

–103,586 recreation visits in July 2014

•Usually, expansion values such as the ‘10% extra’ for Mesa Verde NP are established using some form of

–Observational study (observation only – no questions to visitors), or

–Survey with questions to visitors

•Person-per vehicle multipliers are estimated from observational study conducted by the park over the course of a year