Development of a Crashworthy Tangent End Treatment for Low Speed Curbed Roadways
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
· Height – reduce impacts on
sight distance and allows for use with low profile barriers, guardrail, and
typical concrete barriers/bridge traffic railings shapes.
the above elements will also allow for retrofitting existing barriers with a
crashworthy end treatment.
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
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.
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.
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.
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
· Develop Design Concepts
· Present Concepts to Panel
· Perform Component/Material Testing
· Perform Computer Device Simulations of
· 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
· Develop design drawings of concepts for commonly
· Submit drawings for inclusion in the Task
Force 13 Hardware Guide
· Presentation of final design to AASHTO TCRS
and TRB Roadside Design (AKD20) Committee.
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.
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|
|Index Terms:||Crashworthiness, Barriers (Roads), Roadside structures, Highway safety, |
Safety and Human Factors