Freeway Vehicle Occupancy Data Collection: A Comparison of the Roadside Windshield and Carousel Methods

Vehicle Occupancy refers to the number of people in a vehicle at any given time and is important for many reasons. Data about vehicle occupancy help transportation planners evaluate the performance of current transportation systems and plan for the future accordingly. Many state transportation planning agencies also use vehicle occupancy to help them in taking steps to reduce problems relating to congestion and pollution on the roadways. Vehicle occupancy gives transportation planners valuable information about how people are traveling and helps them evaluate current systems. There are many different methods to collect this data including the roadside windshield method (suitable on low-speed roads) and the carousel method (suitable on high-speed roads). This study compared the results of the carousel method with those of the windshield method to collect vehicle occupancy data on Interstate 26 in the state of South Carolina. The results of this study show that the average vehicle occupancy (AVO) derived from using the carousel method was 1.3080, while the AVO for the surrogate windshield method was 1.3303. The AVOs for the two methods are statistically not different at 5% significance level. These results indicate that the windshield method can be utilized to collect vehicle occupancy data for high speed transportation facilities.