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) Slide 2 Why Guardrail? The main
purpose of guardrail is to reduce the potential for, and severity
of accidents involving vehicles that leave the road Slide 3 Slide 4
Guardrail Saves Lives Just ask this guy! Slide 5 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 Slide 6 Is Guardrail A
Hazard? A guardrail installation is a hazard when... Slide 7 Blunt
End - Flared Terminal Slide 8 Disastrous Results with BCT Slide 9
Modified Eccentric Loader Terminal (M.E.L.T) Slide 10 Turndown
Approach Terminal Slide 11 Blunt End - Bridge Transition Slide 12
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 Slide 13 AASHTO Roadside Design Guide Slide
14 Example of simple barrier installation guideline Slide 15
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 Slide
16 What is the NCHRP Report 350? Slide 17 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. Slide 18 What types of longitudinal
guardrail, guardrail end terminal and crash cushion installations
are NCHRP 350 approved?
http://safety.fhwa.dot.gov/programs/roadside_hardware.htm Slide 19
Longitudinal Barriers Slide 20 NCHRP Report 350 Test Levels For
Longitudinal Barriers Slide 21 NCHRP 350 Approved and Non-Approved
Guardrail (Concrete Barrier Rail not shown) Slide 22 Guardrail on
Steel Post with Steel Block Slide 23 Guardrail on Wood Post and
Wood Block Slide 24 Guardrail on Steel Post with Wood Block Slide
25 Guardrail on Steel Post with Plastic Block Slide 26 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.
606-11A and 606-11B) Slide 27 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 Slide
28 Guardrail End Terminals Slide 29 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 Nations 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 Slide 30 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. Slide 31 NCHRP 350 Guardrail Terminal
Test Matrix Slide 32 ET-Plus With Wood Posts Slide 33 Slide 34
Slide 35 ET-2000 with HBA Posts Slide 36 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) Slide 37 ET-Plus with HBA Posts Slide 38 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 Slide 39
Impact Attenuators Slide 40 Crash Cushion Attenuator Test Matrix
Slide 41 Slide 42 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 Slide 43 Newest Tracc Family Member - Widetracc TL-3 Slide
44 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 Slide
45 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 Slide 46 Transitions/ Bridge Approach
Sections Slide 47 Concrete Bridge Transition Test Slide 48 MDT
Detailed Drawings Guardrail W-Beam, Box Beam, Cable, and Concrete
Barrier Rail Terminal Sections Bridge Approach Sections Impact
Attenuators Guardrail Hardware Slide 49 Additional Information
Scott Keller, P.E. MDT/MSU Design PO Box 174252 Bozeman, MT
59717-4252 (406) 994-1843
