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Section 3: Texas Policy on Bridge Railing

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Overview

All bridges require bridge railing. Bridge-class culverts require safety end treatments, metal beam guard fence, or bridge railing. Roadways elevated by retaining walls require bridge railing or metal beam guard fence for the entire length of the retaining walls.

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  • New bridges. Texas bridge railing on new construction must meet FHWA crash-test criteria as specified in MASH or NCHRP Report 350.
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  • MASH Implementation. Per FHWA memo, all new installations of bridge railing, with contract letting date after December 31, 2019, must be evaluated and approved with MASH crash-test criteria.
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  • Existing bridges. See Chapter 4, "Treatment of Existing Railing" for TxDOT policy on upgrading existing rails.
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Approval of Bridge Railing

A bridge railing type can be approved for use on Texas bridges in any one of the following ways:

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  • It has been successfully crash tested in accordance with MASH or NCHRP Report 350 criteria.
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  • It has been approved for specific uses by FHWA after evaluation of results from successful crash testing based on criteria that predate NCHRP Report 350.
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  • It has been evaluated by TxDOT and identified as similar in strength and geometry to another rail that has been successfully crash tested in accordance with MASH or NCHRP Report 350 criteria.
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Rail Type Selection

Use the greater of the posted speed or design speed at the bridge location to determine the test level required for the railing on the bridge.

All bridges with speeds of 50 mph and above must have railings that meet TL-3 criteria or greater. Bridges with speeds of 45 mph and below must have railings that meet TL-2 criteria or greater.

The AASHTO LRFD Bridge Design Specifications describes Test Level 4 as "taken to be generally acceptable for the majority of applications on high speed highways, freeways, expressways, and Interstate highways with a mixture of trucks and heavy vehicles." Based on this description, bridge railings rated TL-4 as per NCHRP Report 350 or MASH are recommended, but not mandatory, for all bridges carrying the main lanes of Interstate highways and divided highways.

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Metal Beam Guard Fence to Bridge Railing Transitions

Bridge railing on any Texas bridge must connect with roadside metal beam guard fence if it is present. TxDOT provides railing transition details in the TxDOT Design Division Roadway Standards and transition connection details in the TxDOT Bridge Division Bridge Standards. Select the transition appropriate for the speed. Speeds of 50 mph and above require a TL-3 transition. Speeds of 45 mph and below can use a TL-2 or TL-3 transition.

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Protecting the Ends of Bridge Railing

All ends of bridge railings must be protected with the appropriate metal beam guard fence and end treatment, per the Roadway Design Manual, with the following exception.

Roadway classifications of urban and suburban, curbed sections, with speed of 45 mph and less may omit protection if both of these criteria are satisfied:

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  • Bridge railing falls within the line of sight of cross traffic streets or driveways, and
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  • Clear zone width, as provided in Chapter 2 Section 6 of the Roadway Design Manual, is satisfied.

This exception does not supersede the need to protect steep side slopes, in accordance with the Roadway Design Manual. If the criteria are not met or steep side slopes are present, and metal beam guard fence cannot be installed, consideration must be made to extend the bridge railing around the corner of the intersecting street or driveway.

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Railing on Bridge-Class Culverts

Protect the ends of bridge-class pipe and box culverts by providing, in order of preference, safety end treatments, metal beam guard fence, or bridge railing as described in the Drainage Facility Placement section of the Roadway Design Manual regardless of horizontal clearance (clear zone). Bridge railing is frequently not an option with bridge-class pipe culverts. A pedestrian railing used alone is not acceptable for bridge-class culverts; traffic railing or combination railing must protect pedestrians and pedestrian railing from vehicular traffic on bridge-class culverts. For bridge-class culverts with raised sidewalks, use an approved combination railing.

Properly anchor bridge railings on box culverts using the details shown on the Rail Anchorage Curb standard drawing and the details shown on the standard drawing for the selected bridge railing type.

For existing box culverts where bridge rail is required, anchor the railing properly using the details shown on the standard drawing for the selected bridge railing type and the details shown on the Rail Anchorage Curb Retrofit Guide drawing, which applies for fill heights of 2 ft. or less. If the Rail Anchorage Curb Retrofit Guide drawing does not apply, the Bridge Division is available to provide project specific details for the addition of bridge railing.

Metal beam guard fence meets TL-3 requirements and can be provided as an option to bridge railing in the following ways:

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  • If there is 36 in. or more of fill, the posts can be soil-embedded as per standard GF(31)-14.
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  • If there is less than 36 in. of fill but at least 9 in., the low fill culvert post detail shown on standard (31)-14 can be used.
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  • Long span guard fence, shown on standard GF(31)LS-14, can be used for shorter bridge-class culverts provided the clearances required by the standard are met
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Railing on Roadways Elevated by Retaining Walls

Roadways elevated on retaining walls that are in-line with the edge of bridge slab require bridge railing, extended along the retaining wall until the drop-off terminates. The bridge railing and side slopes must be protected with the appropriate metal beam guard fence and end treatment, in accordance with the Roadway Design Manual.

Roadways elevated on retaining walls that are offset from the edge of bridge slab require one of the following railing options:

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  • Bridge railing placed in-line with the edge of bridge slab, extended along the roadway until the retaining wall drop-off terminates. The bridge railing and side slopes must be protected with the appropriate metal beam guard fence and end treatment, in accordance with the Roadway Design Manual.
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  • Metal beam guard fence and end treatment attached to bridge railing on the bridge and extended along the edge of roadway until the retaining wall drop-off terminates and side slopes are protected in accordance with the Roadway Design Manual. Slope requirements behind the metal beam guard fence must also be met.
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  • Metal beam guard fence and end treatment attached to the bridge railing on the bridge at the edge of roadway. Additionally, bridge railing mounted at the face of the retaining wall, beginning behind the metal beam guard fence and extending until the retaining wall drop-off terminates. This bridge railing and the side slopes must also be protected with the appropriate metal beam guard fence and end treatment, in accordance with the Roadway Design Manual.
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Open Bridge Railing

Open rails on Texas bridges enhance the bridge user's view from the bridge and often improve the appearance of the bridge. TxDOT encourages the use of open bridge railing on most bridges crossing a water feature and locations where the view would appeal to users. The cost premium of open bridge railing often may be offset by increased positive perception of the public.

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Sound Barriers

Recent years have produced interest in sound barriers for the sides of highways and on bridge overpasses, particularly in suburban areas. TxDOT does not recommend installation of precast concrete sound barriers mounted on top of concrete bridge railing for these reasons:

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  • The sound barrier mass changes the vehicle impact behavior with the railing.
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  • The sound barrier connections at the top of the railing have not been proven to be adequately anchored.

Sound walls may be placed behind a concrete traffic barrier, with a 2 ft. 10 in. minimum distance from face of traffic barrier to face of sound wall, taking into account posts or pillars in the wall that may project in front of the wall panels.

The Bridge Division has details of a sound wall cast integrally on top of a single-slope concrete traffic railing. This railing with sound wall has been evaluated and approved for TL-4 (NCHRP 350) use. Non-standard bridge slab details or custom foundations are required with this railing.

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Decorative Fencing

Requests to place decorative fencing on bridge rails are frequently made to enhance bridge or project aesthetics. Unless the proposed fencing is proved crashworthy by full-scale crash testing, the following requirements must be met when a decorative fence is added to a bridge rail.

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  • The speed at the bridge must be 45 mph and below.
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  • The fence must be installed on top of or behind a concrete barrier type rail.
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  • The fence must have no component that could become an occupant compartment intrusion threat.
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  • The fence must have a device that prevents the fence or any of its components from falling onto lower roadways, railroads, or pedestrians.

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