Safety Implications of Managed Lane Cross Sectional Elements
CHAPTER 3: SITE SELECTION
Selection of States
Cross sections used for managed lanes vary. Some locations separate the managed lane(s) from general-purpose freeway lanes using an exclusive alignment or using barriers. Other locations use a buffer where the buffer consists of a flush area marked with pavement markings and in some cases with supplemental pylons. In many locations, the separation is only a lane line. For this evaluation, efforts were focused on identifying potential sites in the three Highway Safety Information System (HSIS) states with managed lanes (California, Minnesota, and Washington), and in Texas. Based upon the review of variables available within their crash database, the state of California was selected for the study. Data from Texas was also considered due to the availability of latitude and longitude values for many crashes and the use of pylons at several sites.
Highway Safety Information System Crash Data
California was selected for this study because the state uses a code (Location Type) that classifies crashes as being in the high occupancy vehicle (HOV) lane or the HOV buffer. The California HSIS documentation is available at: http://www.hsisinfo.org/guidebooks/california.cfm. The most recent five years of data available for California was 2007 to 2011. A preliminary filtered dataset of select counties was developed. Table 3 provides the number of crashes within this dataset by code for location of collision. The availability of 15,257 crashes with the HOV code and 437 crashes with the HOV buffer code indicates that the California data can provide valuable insights into HOV (managed lane) related crashes.
The research team also queried the Texas Crash Records Information System for variables that can be used to identify HOV-specific crashes. In the case of Texas, whether the crash occurred on a segment with a managed lane could be assumed when HOV or Managed Lane is included in the variables Local_Use or Rpt_Street_Descr. Texas data offers additional details in extended fields (e.g. longitude, latitude) or as part of the narratives that would have to be obtained separately. The latitude and longitude information allowed the research team to quickly merge the crash and additional geometric data collected for specific sites. Because of the limited number of HOV-related crashes, the evaluation of the Texas data was limited to using all freeway crashes.
Source: Texas A&M Transportation Institute
Selection of Sites
With the quantity of managed lane sites available, decisions were needed to focus efforts so to improve the likelihood of identifying usable sites that fit the objective of this project. The following decisions were made during site selection:
For Texas, segments on the following five freeways met the above criteria: I-635 and US 75 in Dallas and US 290, I-10, and US 59S in Houston. For California, a greater number of freeways met the above criteria; therefore, an additional criterion of being in or near the city of Los Angeles was added. The California study locations were on I-105, SR 134, I-210, and I-405. The Texas locations reflect both pylons and flush buffer segments and both Texas and California provide a mix of buffer widths and lane widths. The project requirements were to include a minimum of 12 sites. The research team identified these 18 corridors (nine freeways with each direction uniquely considered) in case some corridors had to be eliminated due to unexpected challenges with the crash data.
United States Department of Transportation - Federal Highway Administration