| Summary: | Fleet composition and vehicle spacing on roads are important inputs to mobile source emission models and traffic planning. In this paper, we present a novel method that employs an unmanned aerial system (UAS) to capture imagery of stationary vehicle formations at two different intersections and times of the day. The imagery is processed through photogrammetric software to generate 3-dimensional (3D) models of the formations allowing for measurement of the stacking gaps and identification of individual vehicle types for fleet composition evaluation. Statistical tests were performed on the different flight results to assess traffic behavior (both composition and gaps) were similar and can be pooled. In both cases, the variation of fleet composition and gaps were similar. However, the stationary headway gaps followed a logarithmic distribution and had to be transformed after pooling. The final results of the fleet composition measured varied significantly from the estimated mix based on registered vehicles, while the average vehicle spacing was approximately 2.17 m and did not depend on vehicle type, location or time of day. These results were used to prepare a Monte Carlo Analysis model to estimate the total number and types of vehicles on a 1 km road section. The model was extended from stationary traffic to traffic moving up to 20 km/h by assuming a linear increase of the spacing gap. This research paper is one of the first of its kind to study the stacking spaces of mixed fleets at signalized intersections and shows that spacing is dependent more on individual driver behavior than vehicle type. Keywords: UAS, Signalized intersection, Fleet composition, Photogrammetry, Monte Carlo Analysis
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