You asked (1) what is the difference in the crash resistance of a metal guard rail and Jersey barrier, (2) why are there Jersey barriers in the median on some parts of Interstate 95 and guard rails in other areas, and (3) does the Department of Transportation (DOT) plan on installing Jersey barriers on those parts of I-95 where they are not currently installed.

MEDIAN BARRIERS

Connecticut uses standards adopted in National Cooperative Highway Research Program (NCHRP) Report 350 to measure the safety performance of highway features. Most guard rails on Connecticut expressways meet the NCHRP test level 3 standard for median barriers. This means that the guard rail will prevent a pick-up truck traveling 62 mph that hits it at a 20 degree angle from crossing over the median, without causing the truck to flip over. The Federal Highway Administration requires that all new median barriers on expressways and other national highway system roadways at least meet this standard.

A 32-inch tall concrete barrier meets the more stringent NCHRP level 4 standard. This type of barrier will prevent a box truck weighing up to 17,600 pounds from crossing over the median or flipping over under circumstances similar to those used in the level 3 test. A 42-inch concrete barrier will met the NCHRP level 5 standards, which means the barrier will prevent a tractor trailer weighing up to 79,200 pounds from crossing over the median or flipping over under similar circumstances. Connecticut currently uses a 45 inch F shape concrete barrier along many segments of the interstate system. The F shape barrier is similar to a Jersey barrier. (The extra three inches allows the base of the barrier to be resurfaced while still providing protection at the level 5 standard. ) Further information about F shape and other concrete barriers is available online at www. tfhrc. gov/pubrds/marapr00/concrete. htm

Historically, DOT has decided whether to install a median barrier and the type of barrier to use based on several criteria. These include the width of the median, the level of traffic (particularly truck traffic), and the number and types of accidents along different segments of the affected highway. The decisions are also affected by other construction projects on the highway, e. g. , widening projects. Most of I-95 west of Branford currently has concrete median barriers.

DOT's design manual species that a median barrier will be installed on an expressway wherever the median is less than 66 feet wide. Barriers may also be installed on wider medians if a significant number of crashes have occurred. If a segment warrants a median barrier but a wider segment does not, the barrier will be extended into the wider median by approximately 100 feet. The design manual is available online at www. conndot. ct. gov/publications/hdm/cover. pdf (chapter 13 covers median barriers).

The choice of whether to install a guard rail or F shape barrier will depend on the factors noted above. In practice, DOT will install F shape barriers in conjunction with highway widening and reconstruction projects where the median is less than 30 feet wide. Thus, DOT has been installing 45-inch F shape median barriers in conjunction with the Quinnipiac Bridge project on I-95. In the West Haven segment of this project, DOT expects to replace the existing 32-inch barriers with 45-inch barriers during 2009-10. DOT also plans to install F shape barriers in the median of I-95 from Old Lyme to the Rhode Island state line as it widens the expressway from two to three lanes in each direction. DOT is currently preparing environmental impact statements for the project segment between exits 70 and 72 in Old Lyme.

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