A general problem that occurs at many existing highway bridge locations throughout the United States is that the length of need for guardrail required at bridge ends cannot be installed due to conflicts within the existing right of way (ROW) limits. The conflicts may consist of an existing intersecting private driveway, state or local roadway intersection, or other objects that do not allow the placement of the required guardrail length of need. It is not unusual at some existing bridge sites to have 10 feet or less between the end of the bridge and the conflict. Because most Test Level 3 (TL-3) tangent or flared guardrail end treatment systems are normally within the range of 37 to 50 feet in length, there is typically a problem with fitting the end treatment systems and guardrail transitions to the bridge rail at these restricted sites. Additionally, no current short radius guardrail system has been able to meet NCHRP Report 350 or the AASHTO Manual for Assessing Safety Hardware (MASH) Test Level 3 (TL-3) safety performance criteria for high-speed roadways. In many cases, the private or public entity is unwilling to relocate the driveway, intersecting roadway, or another conflict, and the state DOT or local transportation agency is left dealing with a potential safety issue.
Traditional solutions are not very practical and prevent the bridge end and any other hazards around the bridge from being properly protected by a longitudinal barrier. In many cases, the State DOT will require that a design exception be acquired to install anything less than the required length of need with the proper guardrail end treatment. Mitigation of this problem was one of the issues specifically identified in the August 18, 1998 AASHTO/FHWA Agreement on implementing NCHRP Report 350. Previous research with short-radius type systems has either been unable to meet the TL-3 safety criteria and/or has proven unable to meet the space requirements for many of the intersecting roadway sites. Therefore, research was needed to develop an effective method for treating these sites for high-speed facilities.
The objective of the research was to develop guidelines on barrier safety treatment alternatives near bridge ends with restricted rights of way in a format suitable for potential adoption and inclusion as an update to the AASHTO Roadside Design Guide (RDG). These guidelines were to provide a barrier design(s) with a minimum footprint where the required length of need for guardrail at bridge ends cannot be installed due to intersecting roadways, driveways, or other obstructions. The proposed design(s) were to meet minimum TL-3 MASH requirements and be accompanied by required documentation necessary for an “FHWA Eligibility Letter for Reimbursement” application. The guidelines included compliant drawings meeting AASHTO/AGC/ARTBA Task Force 13 (TF13) criteria. The guidelines are meant to be suitable for use by state DOTs and other agencies for balloting and acceptance by the AASHTO Highways Subcommittee on Design through its Technical Committee on Roadside Safety (TCRS).
This project was published as NCHRP Research Report 1013, "Roadside Barrier Designs near Bridge Rail Ends with Restricted Rights-of-Way: A Guide."
The appendices will be available as NCHRP Web-Only Document 334, “Roadside Barrier Designs near Bridge Rail Ends with Restricted Rights-of-Way: A National Survey and Testing Reports.”