Bayesian approach in estimating the road grade impact on vehicle speed and acceleration on freeways

ABSTRACT

This research explores how road grade impacts the operations of light-duty vehicles and heavy-duty express buses on freeways. The Bayesian Hierarchical Model (BHM) used in this research employs three variable levels: trace-level (for individual trip effects), vehicle-level (for individual vehicle effects), and fleet-level (for overall sample effect). The vehicle level parameters represent the effects of specific vehicle performance characteristics and drivers’ behaviors on grade (and the hidden effects of driver behavior associated with the vehicle) and display random impact heterogeneity across vehicles and drivers. Fleet level parameters capture operations across the entire sample set. First-order autoregressive covariance matrices represent auto-correlation of speed and acceleration within the time series of each trace. Significant heterogeneity of road grade impact is observed across vehicles. The study provides a reference to microscopic speed and acceleration choices model considering the impact heterogeneity of road grade across vehicles or drivers on the hilly freeway.

KEYWORDS:

• Road grade
• speed
• acceleration
• Bayesian hierarchical model
• Markov Chain Monte Carlo
• Gibbs sampler
• Metropolis-Hasting (M-H) algorithm
• heterogeneity
• heteroscedasticity
• autocorrelation

Acknowledgment

This work was sponsored by the USDOT's University Transportation Center program via the National Center for Sustainable Transportation. We would also like to thank Dr. Mehmet (Memo) Belgin in Georgia Tech's PACE (The Partnership for an Advanced Computing Environment) Center for his distributed computing technical support.

Declaration of interest statement

The study should be of interest for engineers and modelers focusing on vehicle activity and energy/emissions modeling, as the results can be used to better model energy consumption and emissions by improving vehicle activity input on freeways segments across various grades. It is also of interest for researchers doing traffic simulation speed choices modeling, as the study provides a reference to microscopic speed and acceleration choices model considering the impact heterogeneity of road grade across vehicles or drivers on the hilly freeway.

ORCID

Haobing Liu http://orcid.org/0000-0002-3588-4593

Additional information

Funding

This work was sponsored by the USDOT’s University Transportation Center program via the National Center for Sustainable Transportation.