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Development of Guidance for Attaching Approach Guardrail Transitions to Existing Concrete Bridge Rail Ends

Description:

When an approach guardrail is to be connected to a more rigid barrier, such as a bridge rail, it is necessary to provide a transition to gradually stiffen the rail. Transitions typically include more posts at reduced post spacing, larger posts, a stiffer rail (nested elements and/or thrie beam) and a connection to the bridge rail. The connection provides the anchorage for the approach rail but it also should be designed to reduce the potential for snagging as the vehicle engages the rail.

Typically, approach guardrail transitions is designed with bevels or tapers on the upstream edge of the bridge rail to reduce the potential for snagging. The Midwest Roadside Safety Facility developed a standardized buttress or parapet for attaching the approach guardrail transitions (TRR 2672 - https://journals.sagepub.com/doi/10.1177/0361198118758676) which utilizes such tapers and can be used for new bridge rails. However, there are many different existing bridge rails with a variety of shapes that do not include tapered ends. These can include safety shaped rails that did not have the toe of the barrier beveled.

There is a nation-wide need for the development of a modified MASH guardrail transition for attachment to existing bridge ends. The development of this modified design would provide for a substantial safety improvement when a complete bridge rail reconstruction is not an option. A range of modified designs would allow for the construction of a MASH guardrail end terminal, a section of MGS guardrail, and a MASH transition section. This would allow for the changing from a new MASH approach section to an existing NCHRP-350 level bridge railing. This low-cost safety improvement would allow for the replacement of a large number of systems without having to waiting for a major bridge project.

The research would confirm the most common types of end sections, such as safety shapes, single slope, and vertical ends. The researcher would then develop concepts for adaption of existing MASH guardrail transitions for connection to an NCHRP 350 rail. If a MASH approach transition cannot be used, identify next best option(s) that could be used. This would include the addition of a curb section under the approach transition if necessary.

Objective:

The research would confirm the most common types of end sections, such as safety shapes, single slope, and vertical ends. The researcher would then develop concepts for adaption of existing MASH guardrail transitions for connection to an NCHRP 350 rail. If a MASH approach transition cannot be used, identify next best option(s) that could be used. This would include the addition of a curb section under the approach transition if necessary.

Benefits:

Roadside safety hardware is critical for reducing severe crashes on the nation’s highways. Transitions to bridge rails are critical to reduce the potential for snagging and to provide anchorage. While there is a standardized buttress that has been developed, there is a need for a cost-efficient design for connecting approach guardrail transitions to an existing bridge rail

Related Research:

Development of a Standardized Buttress for Approach Guardrail Transitions, Rosenbaugh, Schmidt, Faller, TRR 2672

The WSDOT has a standard plan C-24.10-01 shows different methods for connecting depending on the width of the curb or if the toe was tapered.

https://www.wsdot.wa.gov/publications/fulltext/Standards/english/PDF/c24.10-01_e.pdf

These connections were developed using engineering judgment and there have been no tests run on these designs.

MASH testing currently under review include Hawaii DOT’s guardrail transition with curb and Texas DOT’s guardrail transition with twisted thrie beam and curb.

Tasks:

Possible tasks include:

• Survey and classification of common existing bridge rail ends.

• Review and discussion of issues that would identify a bridge rail end as a candidate for modification, replacement or other solution.

• Identifying potential modifications needed to adapt an approach transition to match a “family” of bridge rail end treatments

• Modeling of approach transition modifications

• Crash testing transition modifications

Relevance:

The guidance developed will assist state, local and tribal agencies to provide the most practical solution for connecting new MASH guardrail systems to existing bridge rails.

Sponsoring Committee:AFB20, Roadside Safety Design
Research Period:24 - 36 months
Research Priority:Medium
RNS Developer:Scott Rosenbaugh
Source Info:TRB AFB20 Mid-Year Meeting 2019, Reno NV
Date Posted:01/06/2020
Date Modified:01/06/2020
Index Terms:
 
Subjects    
Highways
Design
Safety and Human Factors
Bridges and other structures

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