Presentation on theme: "“You Could Learn a Lot About Guardrail From a Dummy…"— Presentation transcript:
1“You Could Learn a Lot About Guardrail From a Dummy… “You Could Learn a Lot About Guardrail From a Dummy…..(and his crash tests)”Guardrail Basics for Design and Construction Scott Keller MDT Conference January 2007
2Why Guardrail?‘The main purpose of guardrail is to reduce the potential for, and severity of accidents involving vehicles that leave the road’
5Statistics Approximately 42,000 fatalities on U.S. highways annually Nearly 12,000 of these occur as a result of run-off-the-road(R.O.R.) accidentsApproximately 1,200 of the R.O.R. fatalities are caused byguardrail as the first harmful event
6A guardrail installation is a hazard when... Is Guardrail A Hazard?A guardrail installation is a hazard when...
12Guardrail Is Often A Hazard Since Guardrail itself is a hazard, it should be used only as a last option. Before using guardrail:Remove the hazard completely (Trees, Large Rocks, etc.)Eliminate the hazard (fill depressions, holes, etc.)Then, and only then:Protect the hazard with barrierUse the minimum amount of barrier required to protect hazardProtect the barrier end with an approved end terminal
14< Length of Need (LON) > Example of simple barrier installation guideline
15Federal Highway Administration (FHWA) Policy requires the following roadside safety features used on the National Highway System to meet the performance criteria of NCHRP Report 350Traffic BarriersBarrier TerminalsCrash CushionsBridge RailingsLight Pole SupportsSign Post SupportsWork Zone Hardware
17What 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.
18What types of longitudinal guardrail, guardrail end terminal and crash cushion installations are NCHRP 350 approved?
26W-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)
27Plant Mix Overlays and W-Beam Guardrail Three inch (75 mm) tolerance on height of railReplace rail when the overlay exceeds 0.25 feet or 75 mm in thickness
291994 FHWA Memorandum Dean Carlson, Executive Director “…some obsolete roadside hardware or poor practices thought to havebeen upgraded or eliminated …still remain on the Nation’s mainroadway systems”“...FHWA has a responsibility to identify hardware designs andpractices that are no longer acceptable for specific conditions”“…the following nationwide traffic barrier upgrading issues, most ofwhich involve terminals, are identified as needing attention:Replacement of Blunt End TerminalUse of Turn-Down TerminalsBreakaway Cable Terminal (BCT)Terminal Replacement
301994 FHWA Memorandum Dean Carlson, Executive Director Breakaway Cable Terminal (BCT)The BCT does not pass 100 km/hour testing with the 820 kg car.Use of BCT no longer accepted for installation after 1 year ofreferenced memorandum on the approach end of high speed, highvolume roads on the NHS.Existing BCT units should be replaced with crashworthyterminals when units are damaged, or when significant roadwaywork is done in the same area.
36ET-PLUS and SKT 350 Advantages: Softer Ridedown for smaller vehiclesAddress Future Side-Impact Testing CriteriaSuccessfully Tested to NCHRP Report 350Test Level 3 CriteriaEasier to install (New Heads are Lighter)
42TRACC Advantages: NCHRP Report 350 Approved: 6.4 Meter Length Test Level 3 (100 km/hour)Majority of parts are reusable after end-on impactAll-steel construction extends product life andminimizes maintenanceInstalled on Concrete or Asphalt
44Quadguard Advantages: NCHRP Report 350 Approved:6 Bay Design Meets Test Level 3 (100 km/hour)Majority of parts are reusable after end-on impactCollapsible cartridges extend product life andminimizes maintenanceInstalled on Concrete or Asphalt
45QUEST is the newest MDT approved Impact Attenuator Very similar to TRACC in design and appearanceMajority of parts are reusable after end-on impactAll-steel construction extends product life and minimizes maintenance