Dusty R Arrington

Test Level 2 Guardrail-to-Bridge Rail Transition Compatible with 31-in. Guardrail

Many state departments of transportation are in the process of updating their guardrail standards to comply with the AASHTO Manual for Assessing Safety Hardware (MASH) and guidance issued by FHWA on guardrail height. A key feature of the new systems is an increase in rail mounting height from 27 in. to 31 in. A common application of guardrails is shielding motorists from hazards at bridge approaches, including the end of the bridge rail. When a flexible-approach guardrail is attached to a rigid bridge rail, a transition section is needed to transition the stiffness properly from one system to another. A nested thrie beam transition system has been successfully tested to MASH guidelines and is compatible with a 31-in.-approach guardrail. However, it is cost-prohibitive to use this high-speed, Test Level 3 transition on all roadways. A low-cost transition was successfully evaluated under NCHRP Report 350 Test Level 2 (TL-2) impact conditions for use on lower-speed roadways. However, this TL-2 W-beam transition is 27 in. tall and is not compatible with the new 31-in. guardrail systems. This paper describes a new low-cost guardrail-to-bridge rail transition that was successfully developed and tested under MASH TL-2 conditions. The transition is compatible with new 31-in. guardrails and can connect to rigid concrete bridge rails. The transition is considered suitable for implementation on roadways that have traffic conditions appropriate for the use of TL-2 safety hardware. Use of this system would provide significant savings in both material and installation costs compared with high-speed transition systems.

Concrete Roadside Barrier Anchorage Details for 5-in., Cast-in-Place Decks on Prestressed Beams

The Texas Department of Transportation commonly builds bridge spans with adjacently framed, prestressed box beams and slab beams and makes them composite with a 5-in.-thick, concrete, cast-in-place deck (CIPD). The presence of a cast-in-place, concrete overlay allows use of more favorable empirical, live-load distribution equations, which results in more efficient bridge spans. This 5-in.-thick CIPD offers limited depth for anchorage of rail reinforcement. AASHTO Load and Resistance Factor Design Bridge Design Specifications has a limiting hook development length of 6 in. for a No. 4 rail anchorage. With a 5-in. deck thickness and a 6-in. minimum required development length, the rail anchorage reinforcement must be cast in the pretensioned beams to meet specification requirements for rail anchorage strength. This need has made it difficult to ensure adequate development of the rail anchorage reinforcement. The objective of the study reported here, therefore, was to develop barrier anchorage details that would meet the AASHTO Manual for Assessing Safety Hardware (MASH) evaluation criteria, minimize damage to the concrete barrier profile and CIPD, and prevent delamination of the CIPD from the precast beams, which was witnessed in a research project performed at Texas Transportation Institute. The anchorage modifications were evaluated successfully under the Manual for Assessing Safety Hardware Test 3–11 and were considered suitable for roadways with traffic conditions appropriate for Testing Level 3 safety hardware.

Low-Cost Median Barrier Gate

Median barriers are commonly used to separate opposing lanes of traffic on divided highways and to separate managed lanes from general purpose lanes. Concrete median barriers (CMBs) are often preferred on urban freeways with narrow medians because of their minimal deflection and low maintenance. However, long, continuous runs of CMBs limit access of emergency and maintenance vehicles to the other side of a roadway or a managed lane. Implementation of crashworthy median barrier gates at these locations can maintain the desired level of median protection for motorists while offering improved cross-median access for emergency and maintenance vehicles. A new median barrier gate was developed and crash tested. The gate spans a 30-ft opening in a CMB and consists of two vertically stacked 12- x 12- x ¼-in. steel tubes connected to steel end brackets with 2¼-in. diameter steel pins. The gate is economical to fabricate and install. It can be manually operated by a single person and is designed to accommodate reversible traffic flow on both sides of the median and be operable in both directions on each end. The median barrier gate satisfies the criteria for impact performance of Test Level 3 of the Manual for Assessing Safety Hardware and is considered suitable for implementation on divided highways at locations where cross-median access is desired.