Connected vehicle applications promise to transform traffic management and safety. Evaluating the performance of vehicular communication systems in real-world settings benefits from detailed propagation models. Developing such models can be challenging due to the dynamic nature of the vehicular environment. This paper presents an experimental methodology to control and monitor key experimental factors and to efficiently conduct real-world measurements. We tested the Dedicated Short Range Communication (DSRC) technology at 5.9 GHz in a week-long experiment involving 10 vehicles on a major highway under one of the most dense traffic conditions in the United States. We study the repeatability of such measurements for different experiment durations, which may help place earlier propagation studies into context. The experiments show that, with orchestrated vehicle movement in a 2 km section of highway, the pathloss exponent estimation is repeatable within a tolerance of ±0.1 in 11 minutes of measurements for extremely light traffic and in 48 minutes for moderate to heavy traffic.