Presentation on theme: "Guardrail Basics for Design and Construction Scott Keller MDT Conference January 2007 “You Could Learn a Lot About Guardrail From a Dummy….. (and his crash."— Presentation transcript:
Guardrail Basics for Design and Construction Scott Keller MDT Conference January 2007 “You Could Learn a Lot About Guardrail From a Dummy….. (and his crash tests)”
Why Guardrail? ‘The main purpose of guardrail is to reduce the potential for, and severity of accidents involving vehicles that leave the road’
Guardrail Saves Lives Just ask this guy!
Statistics u Approximately 42,000 fatalities on U.S. highways annually u Nearly 12,000 of these occur as a result of run-off-the-road (R.O.R.) accidents u Approximately 1,200 of the R.O.R. fatalities are caused by guardrail as the first harmful event
Is Guardrail A Hazard? A guardrail installation is a hazard when...
Blunt End - Flared Terminal
Disastrous Results with BCT
Modified Eccentric Loader Terminal (M.E.L.T)
Turndown Approach Terminal
Blunt End - Bridge Transition
Guardrail Is Often A Hazard Since Guardrail itself is a hazard, it should be used only as a last option. Before using guardrail: u Remove the hazard completely (Trees, Large Rocks, etc.) u Eliminate the hazard (fill depressions, holes, etc.) Then, and only then: u Protect the hazard with barrier u Use the minimum amount of barrier required to protect hazard u Protect the barrier end with an approved end terminal
AASHTO Roadside Design Guide
Example of simple barrier installation guideline
Federal Highway Administration (FHWA) Policy requires the following roadside safety features used on the National Highway System to meet the performance criteria of NCHRP Report 350 u Traffic Barriers u Barrier Terminals u Crash Cushions u Bridge Railings u Light Pole Supports u Sign Post Supports u Work Zone Hardware
What is the NCHRP Report 350?
NCHRP Report 350 is the research report adopted by FHWA as the standard for determining safe and acceptable performance of roadside features for use on the National Highway System.
What types of longitudinal guardrail, guardrail end terminal and crash cushion installations are NCHRP 350 approved?
NCHRP Report 350 Test Levels For Longitudinal Barriers
NCHRP 350 Approved and Non-Approved Guardrail (Concrete Barrier Rail not shown)
Guardrail on Steel Post with Steel Block
Guardrail on Wood Post and Wood Block
Guardrail on Steel Post with Wood Block
Guardrail on Steel Post with Plastic Block
W-Beam Grading Requirements: §Provide 10:1 or flatter slopes in front of rail and terminal sections. §Provide two feet (600 mm) of soil behind the posts to develop adequate soil resistance. §Use new 7 foot (2.1 M) posts with half-post spacing design in areas that you cannot provide two feet (600 mm) of widening. (See Dtl. Drwg. No A and B)
Plant Mix Overlays and W-Beam Guardrail §Three inch (75 mm) tolerance on height of rail §Replace rail when the overlay exceeds 0.25 feet or 75 mm in thickness
Guardrail End Terminals
1994 FHWA Memorandum Dean Carlson, Executive Director “…some obsolete roadside hardware or poor practices thought to have been upgraded or eliminated …still remain on the Nation’s main roadway systems” “...FHWA has a responsibility to identify hardware designs and practices that are no longer acceptable for specific conditions” “…the following nationwide traffic barrier upgrading issues, most of which involve terminals, are identified as needing attention: u Replacement of Blunt End Terminal u Use of Turn-Down Terminals u Breakaway Cable Terminal (BCT) u Terminal Replacement
1994 FHWA Memorandum Dean Carlson, Executive Director Breakaway Cable Terminal (BCT) u The BCT does not pass 100 km/hour testing with the 820 kg car. u Use of BCT no longer accepted for installation after 1 year of referenced memorandum on the approach end of high speed, high volume roads on the NHS. u Existing BCT units should be replaced with crashworthy terminals when units are damaged, or when significant roadway work is done in the same area.
NCHRP 350 Guardrail Terminal Test Matrix
ET-Plus With Wood Posts
ET-2000 with HBA Posts
ET-PLUS and SKT 350 Advantages: u Softer Ridedown for smaller vehicles u Address Future Side-Impact Testing Criteria u Successfully Tested to NCHRP Report 350 Test Level 3 Criteria u Easier to install (New Heads are Lighter)
ET-Plus with HBA Posts
ET-Plus and SKT 350 Advantages: u NCHRP Report 350 Test Level 3 Approved u Wood Post or Steel Post Options u Tangent terminal reduces installation costs u Majority of parts are reusable after end on impact
Crash Cushion Attenuator Test Matrix
TRACC Advantages: u NCHRP Report 350 Approved: 6.4 Meter Length Test Level 3 (100 km/hour) u Majority of parts are reusable after end-on impact u All-steel construction extends product life and minimizes maintenance u Installed on Concrete or Asphalt
Newest Tracc Family Member - Widetracc TL-3
Quadguard Advantages: u NCHRP Report 350 Approved: 6 Bay Design Meets Test Level 3 (100 km/hour) u Majority of parts are reusable after end-on impact u Collapsible cartridges extend product life and minimizes maintenance u Installed on Concrete or Asphalt
QUEST is the newest MDT approved Impact Attenuator §Very similar to TRACC in design and appearance § Majority of parts are reusable after end-on impact § All-steel construction extends product life and minimizes maintenance