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Section 2: Bridge Railing Retrofit Guidelines

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FHWA Policy

The Federal Highway Administration (FHWA) requires that bridge railing on the National Highway System (NHS) meet requirements of NCHRP Report 350:

“...all new or replacement safety features on the NHS covered by the guidelines in the NCHRP Report 350 that are included in projects advertised for bids or are included in work done by force-account or by State forces on or after October 1, 1998, are to have been tested and evaluated and found acceptable in accordance with the guidelines in the NCHRP Report 350.”1

However, FHWA softens this requirement somewhat by allowing exceptions at the discretion of state transportation agencies:

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  • “Bridge railings tested and found acceptable under other guidelines may be acceptable for use on the NHS.” This is a specific reference to the Horne memo titled “Crash Testing of Bridge Railings.”2
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  • “The FHWA does not intend that this requirement (that new safety features installed on the NHS be proven crash worthy in accordance with the guidelines in the NCHRP Report 350) result in the replacement or upgrading of any existing installed features beyond what would normally occur with planned highway improvements.” This statement is qualified by a requirement that states have a “rational, documented policy for determining when an existing non-standard feature should be upgraded.”
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  • “A transportation agency shall define when extensions, relocation, adjustments, or major repairs to a feature constitute a new installation.” In addition, for 3R projects, “...features that meet the acceptance requirements recommended in NCHRP Report 230, at the discretion of the transportation agency, may remain in place.”3
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Texas Policy

Texas is moving toward full implementation of NCHRP Report 350 crash-test criteria for bridge railing, and Texas policy is to bring all bridge railing to current standards on bridges that are being widened or rehabilitated. TxDOT is required to evaluate bridge railing for conformance to current standards whenever any improvements are made to any bridge or its approach roadway. An existing obsolete railing within a safety improvement project must be brought up to current standards, or else the project must obtain a design exception, providing that railing replacement is scheduled within a reasonable time. Bridge Division staff members are available to advise districts on options.

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Bridge Railing in Pavement Overlay Projects

Minimum heights for most bridge railing types are documented in Chapter 2, Obsolete Railing on Existing Bridges, minimum heights for railing types with no documented minimum height are currently under review. Minimum railing heights must be maintained, even during subsequent bridge maintenance overlays, which should be tapered at a maximum 1 to 10 slope over the width of the shoulder to zero depth at the rail. If minimum rail height cannot be achieved with tapering the overlay, the rail height must be increased to its minimum. The Bridge Division is available to assist when details for raising rail heights are required.

Measure bridge railing height at its inside face from its top to the top of the bridge deck surface.

In a pavement overlay project that includes a bridge, existing bridge railing that does not comply with NCHRP Report 350 may remain in place under the following conditions:

  • It complies with NCHRP Report 230 requirements. The following railing types meet NCHRP Report 230 requirements:
    • Earlier versions of NCHRP-350 compliant railing, with the exception of T4 and C4. (Various versions of T4 with an 18-inch tall concrete parapet are considered compliant. However, versions of the T4 rails built with a 12-inch tall concrete parapet are not compliant. Those rails were usually built before 1967.)
    • T2 or T201, which predate the T221.
    • T202, which predates the T203.
    • T5, which predates the T501 series. For this railing, the first 3 feet from the end of the rail should be tapered in a similar manner to the current T501.
  • It will meet minimum height requirements for that railing type, where the heights are established, after the overlay project.
  • Tapering the overlay down to the toe of the rail over a short distance to achieve a minimum rail height is not permitted. At least 10 feet of flat (1V: 10 H or flatter) pavement must exist in front of the railing.

In general, bridge railing upgrade is not required in the following types of overlay projects:

  • The project is built under TxDOT’s preventive maintenance (or 2R) project design criteria.
  • The project is built under 3R project design criteria and has a design exception if the bridge is on a high-volume (greater than 1,500 average daily traffic) roadway or a design waiver if the bridge is on a low-volume (1,500 or less average daily traffic) roadway.

For more information on TxDOT’s project design criteria, see the TxDOT online Roadway Design Manual. Bridge Division staff members are available to advise districts on requirements for specific projects.

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Transition Upgrades

When roadway guard fence is upgraded but existing bridge railing will remain in place, customized bridge-rail-to-guard-fence transitions may be required. Bridge Division staff members are available to advise districts on options.

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Recommendations

As part of the planning for a bridge that will be widened or rehabilitated, consider the following aspects of the project in the selection of a retrofit railing:

  • Elements of the bridge structure
  • Characteristics of the bridge location
  • Features of the retrofit designs.

Bridge Structure. Review details of the slab and curb reinforcement of the existing bridge to determine if the slab edge is capable of being retrofitted with an adequate new railing. Details of particular importance include the following:

  • Slab thickness
  • Curb width and height and reinforcement
  • Bridge abutment wingwall conditions.

Evaluate the effect of a full-strength retrofit on the shoulder width of the bridge to ensure that a reduction in effective shoulder width or in sight distances at adjacent intersections will not increase the accident rate. Also consider the following:

  • Bridge width, alignment, and grade
  • Type, aesthetics, and strength of existing railing
  • Bridge length and its potential for posting speed limits.

Location. Evaluate details of the location, such as the following, and consider their effect on selection of a retrofit railing:

  • Bridge structure’s height above lower terrain or waterway
  • Approach roadway’s width, alignment, and grade
  • Position of adjacent streets and their average daily traffic
  • Bridge design speed, average daily traffic, and percentage of truck traffic
  • Accident history on the bridge.

Potential Retrofit Design. Carefully review details of potential retrofit designs, such as the following, and consider their effect on selection of a retrofit railing:

  • Placement or spacing of new anchor bolts or dowels
  • Reinforcement anchorage
  • Approach guard fence post positioning
  • Shoulder width required by the new railing.

1. August 28, 1998, memorandum from Henry H. Rentz on the subject of “National Cooperative Highway Research Program (NCHRP) Report 350 Hardware Compliance Dates.”

2. May 30, 1997, memorandum from Dwight Horne on the subject of “Crash Testing of Bridge Railings.”

3. August 28, 1998, memorandum from Henry H. Rentz on the subject of “National Cooperative Highway Research Program (NCHRP) Report 350 Hardware Compliance Dates.”

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