Chapter 6 - Cross Section Elements

6.7. Barriers

6.7.1. Barrier Types

The following barrier types shall be used under the various stated conditions:

• Cable Barrier – This is a flexible barrier capable of deflecting 12-ft. or more when impacted. Barrier is typically used in the grassed medians of interstates and freeways. The designer shall account for the deflection when determining the location of the barrier.
   
• W-Beam Guardrail – A semi-flexible barrier that will deflect up to 5-ft. W-Beam may be used to prevent vehicles from crossing medians, traversing steep slopes or striking objects. Cannot be used ≤ 8-ft. from curb face. Refer to the GDOT Construction Standards and Details for additional guidance for placement of guardrail behind curbs.
   
• T-Beam Guardrail – Similar to W-Beam guardrail, but deflects only 3-ft. T-Beam is used on transitions from W-Beam to a Concrete Barrier. Refer to the GDOT Construction Standards and Details for additional guidance for placement of guardrail behind curbs.
   
• Double Faced Guardrail – Semi-Flexible barrier capable of deflecting 5-ft. Used in medians and other locations to prevent errant vehicles from crossing into opposing traffic.
   
• Single Slope Concrete Barrier – A rigid barrier with little or no deflection. Used for medians or side barrier directly in front of rigid objects that are near the travel way. This includes walls and bridge bents. This is the preferred barrier for Interstates and new construction where Jersey shape barrier is not being retained.
   
• Jersey Shaped Concrete Barrier – Same uses as single slope concrete barriers. May be used on projects where portions of existing Jersey barrier can be retained to provide a consistent design and appearance. Jersey barrier cannot be retained when construction raises the pavement surface by 3-inches or higher than the bottom lip of the barrier

Temporary Barriers 

The design, installation and maintenance of temporary barriers is discussed in the following documents:

• AASHTORoadside Design Guide, Chapter 9
• FHWA Manual on Uniform Traffic Control Devices (MUTCD), part 6
• DOT Specifications, Section 150
• GDOT Construction Standards and Details, Details of Precast Temporary Barrier (Ga. Std. 4961).

Two methods of temporary barrier are used: 

• Method 1 - Must be certified compliant with National Cooperative Highway Research Program (NCHRP) Report 350, Procedures for the Safety Performance Evaluation of Highway Features (1992) “Test Level 3” approved or meets the requirements of GDOT Construction Standards and Details, Details of Precast Temporary Barrier (Ga. Std. 4961). Method 1 barrier is not suitable on bridges where the distance from the centerline of the barrier to the free edge of the bridge deck is less than or equal to 6-ft., measured normal to the barrier.
    
• Method 2 - Must be certified compliant with National Cooperative Highway Research Program (NCHRP) Report 350, Procedures for the Safety Performance Evaluation of Highway Features (1992) “Test Level 3” and does not deflect more than 1-ft. under NCHRP test conditions. A Method 2 barrier shall be used on bridges and bridge approaches where the distance from the centerline of the barrier to the free edge of the bridge deck is less than or equal to 6-ft. measured normal to the barrier.

Refer to the current AASHTO Roadside Design Guide for further discussion on the properties and uses of these barriers.