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.

Evaluating the impact of traffic violations on crash injury severity on Wyoming interstates:An investigation with a random parameters model with heterogeneity in means approach

This study investigated the impact of traffic violations on crash injury severity on Wyoming’s interstate highways.A random parameters multinomial logit(MNL)model with heterogeneity in means was estimated as an alternative to the mixed logit model.This was done to better account for unobserved heterogeneity in the crash data.As per the results,the random parameters model with heterogeneity in means not only exhibited a better fit but also uncovered more insights regarding the factors influencing crash injury severity.The advanced model showed that traffic violations,crash characteristics and environmental characteristics among other factors impact crash injury severity on Wyoming’s interstate highways.With regards to traffic violations,driving too fast for prevailing conditions and driving under the influence of alcohol and drugs were identified as the main violations that significantly influenced crash severity.Among other useful insights,the heterogeneity in mean specification indicated that the likelihood of severe injury crashes is increased by the interactive effect between non-trucks(vehicles not classified as trucks)and driving too fast for conditions.This is a significant implication that high speed behavior by non-truck drivers in adverse weather conditions is ranked as one of the hazardous traffic violations on Wyoming’s interstates.This study provided for the first time important information on the impact of traffic violations on crash severity of crashes that occurred on challenging roadways that characterized by mountainous terrain and severe weather conditions.Results from the study will help enforcement agencies in the state to better identify appropriate countermeasures to mitigate the impact of violations on crash severity.