Boniphace Kutela

Impact of Abandoned and Disabled Vehicles on Freeway Incident Duration

In most cases, abandoned and disabled vehicles are left within the roadway right of ways. It is common to find a vehicle left on the shoulder, median, gore area or on the travel lane for certain period of time. Experience from the state of Tennessee has shown that 78% of the freeway traffic related incidents are due to disabled and abandoned vehicles. It is hypothesized that the longer the vehicle is left unattended within the right of way, the higher the probability of new incidents and secondary crashes. This paper utilized 2004 to 2010 freeway incident data in Tennessee to evaluate the impact of the length of incident durations caused by disabled and abandoned vehicles. Analysis evaluated the impact of these incidents with respect to roadway location, queue lengths, weather conditions, towing times, lane closure, and the source of incident notification. Temporal factors, including the spectra of the time of the day, the day of the week, and the seasons of the year were evaluated with respect to the number of incidents and incident durations. It was found that vehicles left on the left and right shoulders generated more incidents compared to other locations followed by gore areas and the ramps. Parametric hazard based log-logistic survival model was applied to determine the factors affecting the abandoned and disabled vehicles incident duration. Number of closed lanes, length of the queue formed, construction zones, trucks and towing involvement were found to be significantly associated with longer incident duration.

Scanning secondary derived crashes from disabled and abandoned vehicle incidents on uninterrupted flow highways

INTRODUCTION Extent of secondary crashes derived from primary incidents involving abandoned and disabled vehicles are presented in this paper. METHOD Using years 2004 to 2010 incident and crash data on selected Tennessee freeways, the study identified secondary crashes that resulted from disabled and abandoned vehicle primary incidents. The relationship between time and distance gaps before the secondary crash with respect to individual incident characteristics were evaluated through descriptive statistics and linear regression. RESULTS The time and distance gap analysis indicated that a large portion of secondary crashes occurred within 20 min after the primary incidents and within a distance of 0.5 miles upstream. While 76% of incidents involved shoulder, most secondary crashes were related to the closing of right lanes. Overall, 58% of the secondary crashes occurred within 30 min after the occurrence of the primary incidents. Most of the vehicles in the incidents that involved towing and caused secondary crashes were towed or removed out of the travel way within 60 min from the time of occurrence. The study found that most (95%) secondary crashes were property damage only (PDO), while 49% were rear-end crashes. The negative binomial model was used to evaluate the impact of roadway geometry and traffic factors associated with frequency of these secondary crashes. It was found that the posted speed limit, congested segments, segments with high percentages of trucks, and peak hour volumes increased the likelihood of secondary crash occurrence. Roadway segments with wider medians, shoulders, and multilanes decrease the likelihood of secondary crashes caused by abandoned and disabled vehicles as the primary incidents. Practical applications The paper recommends that wider shoulders be provided on any section of freeway to accommodate abandoned or disabled vehicles to avoid blocking of travel lane(s).