Modeling and Evaluating Safety Impacts of Access Management Features in Las Vegas, Nevada, Valley

• Authored by:  T. Mauga
• Co-authored by:  M. Kaseko

Mauga, T. and M. Kaseko, “Modeling and Evaluating Safety Impacts of Access Management Features in Las Vegas, Nevada, Valley,” Transportation Research Record: Journal of the Transportation Research Board, No. 2171, Transportation Research Board, Washington D.C. (2010) pp. 57-65

      This study builds upon the previously established conclusion that access management features can have a significant decrease in crash rates.  Mauga and Kaseko focused on midblock street segments, comparing raised medians with two-way left-turn lanes (TWLTL) in Nevada’s Las Vegas urban area.  The research included crash data between 2002 and 2006 on roads classified by the Nevada Department of Transportation (NDOT) as Category 5, 6, or 7 (principal arterials, minor arterials, and collectors, respectively).  The study used multivariate regression models to incorporate severity of crashes and type of crashes when drawing relationships between crash rates and access management features (which were catalogued using satellite imagery).  Researchers calibrated models for raised median segments, TWLTL, and all segments combined to compare various access management features. 

      The results not only quantified the safety benefits of access management features (i.e. segments with raised medians showed a 23% lower crash rate that TWLTL segments), but also highlighted the extent to which certain features influenced crash rates.  For example, for segments with raised medians, each additional median opening per mile resulted in a 4.7% increase in the total crash rate.  Overall, with all other conditions being equal, segments with raised medians had 21.3% fewer crash rates than TWLTL segments. 

      The study additionally produced a formula to calculate the reduction in crash rate for every driveway that is removed per mile:
 

?y% = 100(e0.0096*(-1)-1) = 1%

Using this formula, a decision to increase the driveway spacing on a one-mile road segment from 258 feet to 400 feet would result in a reduction in crash rates by 13.1%.