New Snapshot Generation Protocol for Travel Time Estimation in a Connected Vehicle Environment

Connected vehicle technology offers great potential to improve the safety and the mobility of a transportation system. Probe data collection is one feature of connected vehicle technology in which vehicles collect information such as their location and speed. Probe data could be used to support various traffic management and traveler information applications. This paper presents the novel R² protocol, used to collect probe data in a connected vehicle environment. The core principle of R² protocol is to collect only vehicle snapshots when a significant change occurs in vehicle speed. Data from a connected vehicle simulation test bed in Boise, Idaho, and a real-world test bed in Oakland County, Michigan, were used to evaluate the proposed protocol. An average speed method and a method with its basis in the reconstruction of vehicle time–speed plots were used to estimate link travel time. Linear regression, cubic spline, and piecewise cubic Hermite interpolation were applied to reconstruct time–speed plots. The proposed R² protocol was compared with three existing protocols: fixed 2-s, fixed 4-s, and SAE J2735. The results from the simulation test bed indicated that the R² protocol not only outperformed the three protocols in error measurement but also required fewer snapshots to achieve the lower-error value. The snapshots recorded by the R² protocol were 30%, 26%, and 4% lower than those recorded by the other three J2735 protocols. The Michigan test bed case study showed that the R² protocol produced fewer errors and needed 11% fewer snapshots than the SAE J2735 protocol.