Guardrail Knowledge Base

Photo Credit: Quality Bridge & Fab, Inc. 

The members of the Short Span Steel Bridge Alliance developed the following knowledge base to provide basic information and resources for the use of guardrails on bridge structures.

Bridge Railing

Generally, bridges are built with bridge railing. Bridge railing is required on projects built with federal funds and may also be required by owner policy. Even when not required, it is generally good practice to use railing on vehicular bridges. When there is guard rail on the road approaching the bridge, an approved MASH-compliant transition must be used to connect the guard rail to the bridge railing.

Galvanized Steel Guardrail Approach

Bridge Rail Test Levels

Bridge rails are categorized by their test level (TL), and there are six level, TL-1 through TL6. The performance expectation for each level increases from TL1 to TL6, and the vehicles and vehicle speeds used for testing bridge rails change in association this these levels. For example, TL-1 rails are tested with a pickup track and a small car at 31 mph; TL-2 rails are tested with a pickup truck and a passenger car at 44 mph; and at TL-6, tests are conducted with the same two vehicles but at 62 mph and with a tractor-tank trailer at 50 mph.

Owners establish policy for which highways and situation require which TL of bridge rail. Proscription of TL-2 and TL-3 are common for non-interstate rural highways, and TL-3 through TL-5 are common for interstates and urban highways.

Galvanized-Powder Coat Railing

Standard Bridge Rails

To receive a particular TL designation, bridge rails must be tested with in accordance with the TL level and pass the test. Testing is generally sponsored by the owner who develops the bridge rail, and usually it is state DOTs who sponsor the test. However, test results are not just valid for the test sponsor. Therefore, it is common for state DOTs to use bridge rails that have been crash-tested by other DOTs.

Pennsylvania HT Bridge Barrier

Requirements SSSBA Candidate Bridges

The bridge rail requirements for candidate short span bridge projects (less than 140 feet) depend upon the requirements of the owner. Each DOT has requirements for bridges built on bridges under the DOT authorities.

Generally local owners build bridges with railing that conforms with the DOT requirements for their state, but this may or may not be customary or required; rules and practices vary from state to state. Therefore, on candidate short span bridges, it is generally a safe assumption that the state DOT rules for bridge railing will apply to the bridge in question, even if the bridge is not being built by the DOT. The owner of the candidate bridge should be able to provide clarity about what polices and practices apply.

Side Mount Bridge Railing

Resources

The following are resources that may be helpful regarding bridge railing:

Federal Highway Administration: Frequently Asked Questions: Barriers, Terminals, Transitions, Attenuators, and Bridge Railings

Task Force 13: TF13 Guide to Bridge Railing Systems

AASHTO: AASHTO T-7 Guardrail and Bridge Rail Committee; & Technical Training Solutions

Ohio Department of Transportation (Sponsor): Evaluation and Design of a TL3 Bridge Guardrail System Mounted to Steel Fascia Beams

Transportation Research Board: Development of a Bridge Railing Optimized for Rural, Low-Volume Roads