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Crashworthiness of Barrier Attachments

Description:

Concrete median barriers have been used throughout the nation as permanent rigid barriers in medians to separate traffic and on roadsides to shield hazards. Typically, these barriers are crash tested and considered crashworthy according to National Cooperative Highway Research Program (NCHRP) Report 350 or more recently the American Association of State Highway and Transportation Officials (AASHTO) Manual for Assessment of Safety Hardware (MASH). Due to space restrictions, hardware such as signs or luminaire poles needs to be attached on top of such barriers. However, when signs or light poles are attached on top of barriers, they potentially reduce the crashworthiness of the barrier and increase the risk to occupants of vehicles impacting the barrier and attachment, or to occupants in other vehicles in vicinity of the impact. There are few research studies on how a barrier with hardware attached on top would perform when impacted by an errant vehicle.

The AASHTO Roadside Design Guide (RDG-2011) currently does not provide guidance for attachment of hardware on top of barriers. Section 4.5.1 does indicate that several state agencies mount luminaires on top of concrete median barriers, a practice that often requires modification to the luminaire support, median barrier, or both. Section 4.5.1 also indicates that a consideration in this design is likelihood of truck impacts, which could snag on the support or bring down the support that might present a risk to opposing traffic.

There is a need for additional design, testing, evaluation, and acceptance of barrier attachment combinations that cover a wide range of barrier and hardware configurations that will be crashworthy when attached on top of concrete barriers in medians and on the roadside including bridges and tunnels. Sign placement on median barriers is becoming more prevalent, especially on multi-lane divided highways adjacent to HOV and HOT lanes, and for evacuation routes where traffic is reversed during hurricanes. Hardware being attached to barriers include small sign supports, large cantilever and overhead sign supports, pedestrian railings, bicycle railings, glare screens, security chain link fence, conventional and high mast luminaire poles, and noise barriers. There is currently minimal design guidance available for selection and attachment of hardware on top of barriers in medians and on the roadside that will ensure continued crashworthiness of the barrier.

There is also a need for performance evaluations to determine the extent of any safety problems associated with existing installations and to evaluate the relative risks and/or benefit/cost analysis of providing crashworthy barrier attachments versus other options (e.g., no barrier attachments or non-crashworthy barrier attachments).

Objective:

The objective of this research is to:

a) Identify the extent of any safety problems associated with existing barrier attachment combinations;

b) Identify existing crashworthy barrier attachments (MASH) and recommend new or modified barrier attachments to Panel for crash testing;

c) Develop risk-based design guidance for selection of crashworthy barrier attachments and non-crashworthy barrier attachments on existing or modified concrete barriers;

d) Crashworthiness of barrier attachments will be evaluated based on MASH Test Level 3 impact which is controlled by the pickup truck test due to its height. However, Test Level 4 should also be evaluated to determine post-impact trajectory hazard of such attachments on median barriers.

The research should identify from a survey of user agencies existing design guidelines and common types of barrier attachments currently being used including any observed operational problems. Assess the performance of the most common barrier attachment combinations that have not been crash tested through nonlinear finite element simulation, and recommend existing or modified attachment/barrier combinations for further evaluation and crash testing.

Benefits:

Currently there are few known barrier attachments that have been successfully crash tested.

More and more user agencies are installing hardware on barriers to communicate with drivers including traffic and emergency information. Hence, providing crashworthy barrier attachment combinations is becoming more important to reduce risk to the travelling public. There is also increased use of hardware on barriers on median barriers for HOV and HOT lanes, and for evacuation routes on divided highways where traffic is reversed in advance of hurricanes or other emergencies.

User agencies need risk-based design guidelines with one or more cost effective crashworthy barrier attachments designs available from this research instead of using designs with unknown performance and risk.

Related Research:

Past and current research and guidance related to barrier attachments has focused primarily on the following areas:

a) State of practice and extent of DOT usage of barrier attachments. NCHRP Synthesis 465 (2014) “Permanent Signs Mounted on Median Barriers” included a comprehensive survey of state DOTs summarizing types of signs and supports being attached to the top of rigid median barriers and level of consideration some practices give to potential safety concerns. The Synthesis was limited to only include permanent signs mounted on concrete median barriers.

b) Establishing Zone of Intrusion (ZOI) envelopes for common barrier types subjected to standardized crash tests. Several studies established ZOI envelopes for a limited number of barrier designs using NCHRP Report 350 impact Test Levels 2 through 4. These ZOI envelopes are summarized in Chapter 5 of the RDG-2011. NCHRP Project 22-34 project is anticipated to establish updated ZOI envelopes using MASH Test Levels (expected completion in 2021).

c) Crash testing of specific barrier/attachment combinations. Though limited, some crash tests have been performed to evaluate the performance and acceptability of specific attachments mounted on concrete barriers, such as fixed small sign supports and luminaire poles.

Past and current research efforts directly related to evaluating crashworthiness of common barrier attachment combinations is limited.

Implementation:

The plan to get information sufficient enough to implement in the field such as but not limited to:

a) Detailed construction drawings and specifications of crashworthy barrier attachments;

b) Design guidance for risk-based selection of crashworthy and non-crashworthy barrier attachment types and combinations for median and roadside installations for a wide range of design speeds and traffic volumes for future inclusion in the RDG.

Sponsoring Committee:AFB20, Roadside Safety Design
Research Period:24 - 36 months
Research Priority:Medium
RNS Developer:Mark Ayton, Eric Lohrey, Akram Abu-Odeh
Source Info:2018 AFB20 Midyear Meeting, Austin, TX
Date Posted:01/15/2019
Date Modified:01/24/2019
Index Terms:Highway safety, Barriers (Roads), Crashworthiness, Benefit cost analysis,
Cosponsoring Committees: 
Subjects    
Highways
Design
Safety and Human Factors

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