In National Parks across the country planners are currently experimenting with the use of automated counting devices as a means for estimating visitor use on trails. However, little is understood in regards to counter accuracy due to just recently becoming routinely used. Calibration as a result is becoming a standard practice to increase the accuracies of the data received. Even with this increase in use though, little research has been performed to better understand where calibration correction coefficient values should lie based on specific trail characteristics. This study contributes to the understanding of calibration and counter accuracy by using passive-infrared trail counters and time-lapse photography from May to September of 2012 to evaluate if the trail characteristics use, width, and slope are correlated with the correction coefficients received after calibration within Sequoia and Kings Canyon National Parks. Results found that strong correlations at a 95% confidence interval exist between the examined trail characteristics width and slope, and the trail calibration coefficients received. These results represent both an initial step to better understand how certain trail characteristics influence trail counter accuracy, suggests what methods are most preferable to increase these accuracies when calibrating, and encourage managers to use more stringent forms of calibration
