Author: Lima Kopitch

Publisher:

Published: 2011

Total Pages: 0

ISBN-13:

Accidents are the largest source of external costs related to transportation in the United States with annual costs estimated to exceed $200 billion per year. Incidents also create traffic backups and delays that can result in secondary incidents (i.e., collisions that occur as a result of other incidents). Although incident management has received a lot of attention from academics and practitioners alike, secondary incidents have so far been somewhat neglected. The main purpose of this dissertation is to investigate empirically whether the implementation of changeable message signs (CMS), which are one Intelligent Transportation System tool, can reduce secondary collisions. After reviewing previously published methods for estimating secondary accidents, I implement a Binary Speed Contour Map approach to detect secondary incidents using PeMS data. I also estimate the extra time lost to congestion because of incidents. My study area is a portion of Interstate 5 that stretches 55 miles from the Mexico-US border to Northern San Diego County, CA. This freeway portion has an average annualized daily traffic volume of 230,000 vehicles. My unique dataset includes incident data for 2008 combined with detailed weather data, elements of freeway geometry, and information about CMS usage. I identify a total of 9,003 incidents in my study area in 2008. Using the BSCM approach, I find that 3.7 percent of collisions were secondary incidents. Moreover, my statistical model shows that incidents occurring during evening peak hours on Fridays or during midday on weekends are more likely to result in secondary crashes as do incidents with injuries or fatalities, incidents that involve more vehicles or trucks, or incidents that take place when the pavement is wet. Conversely, secondary crashes are less likely to occur in areas with a complex geometry (perhaps because drivers are more cautious there) or for incidents taking place on the side of the freeway. More importantly, changeable message signs (CMS) decrease the occurrence of secondary crashes. The maximum effectiveness of a CMS is approximately 11.75 miles for a range of 23.6 miles. Finally, annual incident-related congestion is approximately 1.9 hours per freeway vehicle, which represents five percent of the 37 hours of annual traffic delay experienced by the average San Diego motorist.