Impact of combined alignments and adverse weather conditions on vehicle skidding

Roadways in Wyoming are characterized by challenging horizontal profiles, vertical profiles, a combination of the two and adverse weather conditions, all of which affect vehicle stability. In this study, we investigated the impact of different operating speeds when negotiating combined horizontal and vertical curves under unfavorable environmental conditions on Wyoming's interstates via vehicle dynamics simulation software. The simulation tools provided the acting forces on each tire of the vehicle and the side friction (skidding) margins. This allowed for examining the interaction between vehicle dynamics and road geometry in such alignments. Also, linear regression analysis was implemented to investigate the skidding margins based on the simulation results to demonstrate when a vehicle is more likely to deviate from its desired trajectory. Specifically, this examines the contributing factors that significantly influence the skidding margins. The results indicated that: 1)the skidding margins are dramatically decreased by adverse weather conditions even with lower degree of curvature and gradient values of combined curves and more particularly at higher operating speeds conditions. Increasing the vehicle speed on the curve by 10%, the skidding margin dropped by 15%. 2) Compared to heavy trucks and sports utility vehicles (SUVs), passenger cars require the highest side friction demand. 3) The effect of applying brakes on vehicle stability depends on the road surface condition; applying the brakes on snowy road surfaces increases the potential of vehicle skidding especially for heavy trucks. This study assessed the curve speed limits and showed how important to assign safe and appropriate limits speed since the skidding likelihood is significantly sensitive to the vehicle speeds. This study is beneficial to Wyoming's roadway agencies since hazardous sections having combined horizontal and vertical curves are identified. Also, critical situations that require additional attention from law enforcement agencies are pinpointed. Finally, recommendations that are valuable to roadway agencies are made based on this study's findings.