Highway rest areas provide several functions for travelers, including a chance to use the restroom, walk around, stop for a meal, sleep for a while, or pause to use a cellular phone. These activities directly influence dwell time, that is, the time that the traveler in a vehicle spends using a rest area. According to the activity performed at the rest area, the duration of dwell time varies from short to long. Existing information and guidance on parking dwell times at rest areas are generally outdated and are inconsistent among sources. A study was conducted by collecting and analyzing dwell time data from three rest areas in Montana: two located along Interstate highways and one located at the intersection of two state highways. The results showed that the mean dwell time at the three study sites ranged from 14 min 15 s to 23 min 20 s. When dwell times were examined by vehicle type, heavy vehicles had the greatest mean dwell time, followed by recreational vehicles and then cars. Examination of mean dwell times for short- and long-term parking found the short-term means to vary from 8 min 37 s to 10 min 26 s and the long-term means to vary from 4 h 41 min to 5 h 26 min. When data were separated by day and night, average dwell times during the day were significantly shorter than those during the night. This paper updates estimates for rest area dwell times to better represent the current practice and provides a better understanding of the variables that could affect dwell times.