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.

Texas Data

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.

Table 3. California, number of crashes by location type for several counties.

Location Type	Code	2007	2008	2009	2010	2011	Total
Does Not Apply	-	85	66	100	2	76	329
Unknown Type	---	11527	10159	9820	9969	10764	52239
Beyond Median Or Barrier Stripe - Driver's Left	A	208	161	194	181	255	999
Beyond Shoulder - Driver's Left	B	2455	2386	2296	2435	1941	11513
Left Shoulder Area	C	61	60	62	58	45	286
Left Lane	D	17185	14726	13951	15329	15965	77156
Interior Lanes	E	19716	18324	17864	18692	20130	94726
Right Lane	F	13280	12413	12104	12450	13538	63785
Right Shoulder Area	G	428	392	331	359	312	1822
Beyond Shoulder - Driver's Right	H	2349	2173	2197	2295	2009	11023
Gore Area	I	39	34	22	14	25	134
Other	J	489	393	397	442	389	2110
HOV Lane	V	3603	2924	2710	3011	3009	15257
HOV Buffer	W	78	39	84	106	130	437
Grand Total	All	71503	64250	62132	65343	68588	331816

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:

• Focus on sites with one (rather than two) managed lane(s) per direction.
• Eliminate sites that have reversible operations.
• Select sites where the managed lane is operational 24 hours per day, seven days per week.
• Focus on locations with a flush buffer with or without pylons. In other words, eliminate sites with concrete barrier separation between the managed lane and the freeway general-purpose lanes.
• Seek sites that represent a range of buffer widths.

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.