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Development of a Crashworthy Tangent End Treatment for Low Speed Curbed Roadways

Description:

Roadside barriers installed in low speed urban environments often have limited space available to include adequate length of need or apply currently available crashworthy end treatments. With the increasing interest in multimodal transportation, the demand for appropriate barrier solutions to address roadside safety issues in low speed urban and suburban conditions has increased. These environments often have closely spaced intersections/driveways, improvements intended to encourage bicycle and pedestrian travel, physical limitations to the available lateral offset, and commonly involve curbed roadways sections. Because of the physical space limitations, barriers are frequently installed without a crashworthy end treatment (e.g., sloped end treatments on concrete barrier), or employ systems that have not been evaluated for use in combination with curbs (e.g., crash cushions), and/or involve compromises with respect to length of need (i.e., use of gating hardware). Because barriers in these locations are normally installed in combination with curbing, terminals commonly cannot be flared to avoid conflicts with adjacent pedestrian or bicycle accommodations.

As a result of these constraints, it’s anticipated that a viable end treatment for barriers in these environments needs to minimize:

· Length – allow for installations along roadways with longitudinal constraints (i.e. discontinuities for intersections, driveways, predestination crossings, etc.),

· Width – have a narrow cross-section to reduce impacts on infrastructure and adjacent pedestrian pathways.

· Height – reduce impacts on sight distance and allows for use with low profile barriers, guardrail, and typical concrete barriers/bridge traffic railings shapes.

Minimizing the above elements will also allow for retrofitting existing barriers with a crashworthy end treatment.

Objective:

The objective of the research is to develop a MASH TL-2 Tangent End Treatment that minimizes the required length, width, and height of the system, and can be used in common conditions found in urban areas, specifically in combination with 6” vertical curb (minimum height), and that can be transitioned into either; TL-2 low profile, TL-3 F-shape concrete, and semi-rigid w-beam barrier systems. The final product will be non-proprietary system drawings and specifications that will allow for component manufacturing and installation.

Benefits:

Much emphasis has been made recently by AASHTO, FHWA, and state DOT’s themselves in promoting the importance of multimodal solutions to address congestion, environmental, and livability concerns. These solutions often involve development of accommodations and improvements that change the roadside environment, involve the need to provide barriers to mitigate issues associated with a more livable street environments (e.g., trees, poles, landscaping, etc.). Low profile barriers designed to address risks at lower speed conditions (TL-2) are often preferred, because they are more consistent with public expectations associated with these context sensitive designs. While MASH compliant versions of these low profile barriers are in the process of development, there remains the need for crashworthy terminals for these barriers that are also designed to be consistent with the urban landscape.

In the absence of progress on context appropriate, low speed, low profile barrier terminals, application of these barriers as a part of an overall multimodal solution will be limited. However, with the introduction of a flexible, low speed tangent terminal, highway and urban designers will have confidence to provide the trees, poles, and other features associated with these urban, multimodal improvements, confident that they can employ both barriers and terminals that address both these popular livability design objectives and roadside safety concerns. Without this research, it is expected that livability designs will still be developed but will include potentially hazardous features without being appropriately shielded by barrier and crashworthy end treatments.

Related Research:

While there is a significant amount of existing literature that will help guide the decision-making process and concept development (e.g., effects of curb on vehicle trajectory, crash testing simulations of roadside hardware, evaluations of transitions, etc.) there is no known existing research that specifically addresses the Development of a Crashworthy Tangent End Treatment for Low Speed Curbed Roadways.

Tasks:

The research contractor will likely have to perform these major tasks:

· Comprehensive Literature review to determine critical design elements, evaluate potential components, and establish baseline for system design concepts

· Determine appropriate curb heights (Minimum 6” Vertical)

· Develop Design Concepts

· Present Concepts to Panel

· Perform Component/Material Testing

· Perform Computer Device Simulations of Selected Concepts

· Present Simulations to Panel

· Proof of Concept Crash Testing

· Validation of Computer Simulations

· Full Scale Crash Testing to MASH TL-2 Terminal/Crash Cushion testing matrix

· Development of design drawings and construction specifications needed for the manufacturing and installation of the system

· Develop design drawings of concepts for commonly needed transitions

· Submit drawings for inclusion in the Task Force 13 Hardware Guide

· Presentation of final design to AASHTO TCRS and TRB Roadside Design (AKD20) Committee.

Implementation:

The results of this research will be used by state standards engineers to update the standard drawings, construction specifications, and design manuals to provide a MASH TL-2 crashworthy tangent end treatment for low speed curbed roadways. The Task Force 13 Hardware Guide could assist implementation through inclusion of design details and component standardization. Implementation would also be supported with presentations to AASHTO and TRB membership.

Relevance:

The results of this research will provide roadside safety design practitioners and roadway owner agencies a low speed tangent crashworthy end treatment (i.e., MASH TL-2) that minimizes the length, width, and height required to safely terminate rigid and semi-rigid barrier systems installed in combination with curb.

The AASHTO Strategic Highway Safety Plan and the FHWA Roadway Departure Strategic Plan both highlight the importance of reducing the incidence and severity of roadside crashes. The AASHTO Technical Committee on Roadside Safety has also prioritized the combined use of ISPEs, computer simulation, and full-scale crash testing in its strategic plan.

Sponsoring Committee:AKD20, Roadside Safety Design
Research Period:24 - 36 months
RNS Developer:Derwood Sheppard, John Donahue
Source Info:AKD20 Summer Meeting 2020
Date Posted:01/04/2021
Date Modified:02/10/2021
Index Terms:Crashworthiness, Barriers (Roads), Roadside structures, Highway safety,
Cosponsoring Committees: 
Subjects    
Highways
Design
Safety and Human Factors

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