FDOT Standard Plans Index 536-001: Guardrail

Design Criteria

Design Criteria FDOT Design Manual ( FDM ) , 215 ; AASHTO Roadside Design Guide , 4th Edition; NCHRP Report 350 , Test Level 3 Criteria; AASHTO Manual for Assessing Safety Hardware (MASH) , Test Levels 2 & 3 Criteria; Task Force 13, Guide to Standardized Roadside Hardware

Design Assumptions and Limitations

Design Assumptions and Limitations For guardrail requirements, including hazard setbacks, crash test level classification, and placement in relation to curb, shoulder gutter, and the Edge of Traveled Way, see FDM 215 . For guardrail requirements regarding Box Culverts, also see FDM 215.4 . A.

General: Index 536-001 defines guardrail segments including General Guardrail (TL-3), End Treatments (TL-2 or TL-3), and Approach Transition Connections to Rigid Barrier (TL-2 or TL-3) that will be used together to design a complete guardrail configuration on a project-specific basis. Note that differing test level (TL) segments are compatible, but their applicability must meet or exceed the design speed of the roadway per FDM 215 . The design of guardrail requires that certain segments and features be shown and labeled correctly in the plans, where the requirements of the Index are not violated including section geometry, adjacent pavement, and grading.

For guardrail connections to Rigid Barrier, Index 536-001 applies only to newly constructed bridge Traffic Railings and Concrete Barriers or where the complete Approach Transition Connection to Rigid Barrier details shown in this Index can be installed without conflicting with existing Traffic Railings, structures, or bridge approach slabs. For guardrail systems connecting to existing bridge Traffic Railings that conflict with Index 536-001 details, use the details, layouts, and length table methodology shown in Indexes 536-002 , 521-404 , and 521-405 . B.

Shielding Hazards – Determining Length of Need and Begin/End Guardrail Stations: The standard method of determining guardrail placement for shielding hazards is based on the Runout Length and the Length of Need calculation in the AASHTO Roadside Design Guide (RDG) , 4th Edition. See the FDOT 'Guardrail Length of Need (LON)' program (Excel spreadsheet) for additional information and assistance with determining Begin/End Guardrail Stations for shielding various hazard configurations. The program is located in the Design Tools column of the Standard Plans website.

Index 536 - 001 Guardrail See FDM 215 for the Clear Zone concept, hazard definitions, and warrants for roadside barrier usage. The back of single-faced guardrail, including posts and other hardware exposed to traffic, requires shielding if located within the Clear Zone. Additionally, Trailing Anchorages require shielding if located on the approach end of guardrail and within the Clear Zone.

For example guardrail configurations for shielding hazards, including ends of rigid barriers, see Index 536-001 layouts and Examples 1 & 2 below. C. End Treatments: An End Treatment segment is required for all exposed guardrail ends where the guardrail does not smoothly connect into another barrier type.

End Treatments are divided into three types: 1. Trailing Anchorages: Place a Trailing Anchorage on the downstream ends of all guardrail runs with respect to the nearest traffic lane, except where the location is within the approach Clear Zone of an opposing traffic lane. Locate the end post of the Trailing Anchorage at least 25 feet downstream of any hazards being shielded.

For constrained conditions, such as side streets or driveways, extend the Trailing Anchorage downstream from hazards as far as practical. Trailing anchorages may be used with both flush shoulders and raised curb conditions. 2.

Approach Terminals: Place an Approach Terminal on the approach ends of guardrail runs for locations within the Clear Zone of an adjacent traffic lane. Place Approach Terminals straight and parallel to the adjacent traffic lane, as shown in the Index. When placing guardrail within tight radial roadway segments, such as freeway entrance or exit ramps, locate Approach Terminals outside of the radial segment (i.e., extend guardrail length to allow for a tangent section of guardrail).

a. Terminal Types: Approach Terminals are defined in the Index and classified as Parallel and Double Faced. i.

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Payment

Payment for any additional curb type begins at Section F-F or G-G as shown in the Index. For guardrail connections to Rigid Barrier ends that are outside of the Clear Zone and do not require shielding, the shorter Trailing End Transition Connection (Trailing Trans.) may be used per Index 536-001 details. Per the Basis of Estimates, a separate Pay Item is required for all Transition Connections to Rigid Barrier (Approach or Trailing).

For connections to existing bridge Traffic Railings that conflict with Index 536-001 details, use Indexes 536-002 , 521-404 , and 521-405 . E. Pipe Rail: Pipe Rail segments are required where Steel Posts will be located within 4 feet of sidewalks or shared use paths in the final condition.

Do not place Pipe Rail inside of End Treatment and Approach Transition segments ('LE', 'LT', 'LA', and Crash Cushion segments); specify timber posts where needed. Pipe Rail also must not be used for TL-2 guardrail, so timber posts are the required pedestrian treatment for TL- 2 guardrail. Pipe Rail requires a separate Pay Item.

Where possible, provide the Contractor an option of either Timber or Steel Posts by including Pipe Rail in the Plans quantities (i.e. assume Steel Posts are used, unless the design prohibits the use of Steel Posts for other reasons). Where Pipe Rail cannot be used due to project-specific restrictions, specify use of timber post guardrail and end treatments instead.

F. Rub Rail: Place Rub rail on the median side of Double-Faced Guardrail, where approaching median slopes are greater than 1:10 per the Index. Additionally, rub rail may be used for the consideration of motorcycles per FDM 215 .

4 . Do not place Rub Rail inside of Index 536 - 001 Guardrail End Treatment segments (‘LE’ or Crash Cushion segments). Rub Rail requires a separate Pay Item.

G. Deep Posts: Where right-of-way is restricted (i.e. constrained condition), Deep Posts may be used with the slope break located at the post centerline as defined per the Slope Break Condition in the Index.

Due to unique challenges with maintenance and erosion at the slope break, Deep Post usage requires a special approval per FDM 215 . Deep Posts are only permitted for segments with a post spacing of 6'-3" or less. Deep Posts require a separate Pay Item (Special Guardrail Post).

H. Modified Mounts - Special Posts: When the required post spacing results in placement of posts atop concrete structures, concrete sidewalks, or subsurface utilities, use the Special Steel Posts, Frangible Leave-Outs, or Encased Post options, respectively, as defined in the Index and Specification 536 . Before using Special Posts, first consider alternative design geometry.

Do not place Special Posts inside of End Treatment segments ('LE', 'LT', and Crash Cushion segments). Special Posts require a separate Pay Item. Special Steel Posts are intended only to accommodate minor discontinuous structures such as drainage inlets.

Limit placement to 3 consecutive posts. Frangible Leave-Outs require steel posts. Where practical, specify steel posts in adjoining guardrail runs for consistency.

Encased Posts are intended only to avoid conflicts with single point or laterally running underground obstructions. Limit placement to 3 consecutive posts. I.

Guardrail Taper Rate: Guardrail locations will typically run parallel to traffic lanes, but certain conditions, such as a median crossover or a change in typical section, will require a change in guardrail offset. Use a linear taper (a.k.a. flare) to accommodate such changes in guardrail offsets.

See the layouts in the Index as well as Example 1 below, where tapers are denoted by 'Begin/End Taper Station' callouts. The 'Begin/End Taper Station' and offset callouts will define the linear Taper Rate for construction. For Design Speeds ≤ 45 MPH, use a maximum 1:10 Taper Rate.

For Design Speeds > 45 MPH, use a maximum 1:15 Taper Rate. Where space is limited, Taper Rates may be refined by following the guidance of the AASHTO RDG . J.

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