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Session 9

Session 9. Course Summary. Course Outcomes. Explain the “Roadside Safety” Problem, the Clear Zone Concept, and Warrants for Guardrail Explain How Standard Guardrail Systems Function Describe the Installation Principles Necessary for Proper Guardrail Operation

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Session 9

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  1. Session 9 CourseSummary

  2. Course Outcomes • Explain the “Roadside Safety” Problem, the Clear Zone Concept, and Warrants for Guardrail • Explain How Standard Guardrail Systems Function • Describe the Installation Principles Necessary for Proper Guardrail Operation • Apply Special Guardrail Applications to Unique Situations • Describe How End Treatments Function and Proper Installation • Be Able to Inspect Guardrail Systems for Proper Installation

  3. Summary • THERE IS A ROADSIDE SAFETY PROBLEM • OUT OF OVER 40,000 HIGHWAY FATALITIES A YEAR, 30+% ARE RUN-OFF-ROAD CRASHES • THE MOST COMMONLY STRUCK OBJECTS ARE TREES

  4. Clear Zone • THE AREA AVAILABLE FOR SAFE TRAVERSAL GET AS MUCH AS PRACTICAL

  5. Roadside Guardrails NCHRP 350 – TESTING AND EVALUATION 4500# PICK-UP BIG CHANGE • GUARDRAIL SYSTEMS • FLEXIBLE (>5’) – CABLE, WEAK POST W-BEAM • SEMI-FLEXIBLE (2-5’) – BOX BEAM, STRONG POST W- AND THRIE-BEAM

  6. Median Guardrails • MEDIAN GUARDRAIL SYSTEMS • LOW TENSION CABLE • HIGH TENSION CABLE (MOSTLY PROPRIETARY) • METAL BEAM (BOX, W-, THRIE-)

  7. Roadside Guardrails • WARRANTS • GUARDRAIL MUST BE LESS OF A HAZARD THAN WHAT IT’S SHIELDING METAL GUARDRAILS MUST DEVELOP TENSION CONTINUITY AND HAVE PROPER HEIGHT

  8. Roadside Guardrail Location • AS FAR AWAY AS POSSIBLE as long as • DEFLECTION – STIFFEN IF NEEDED • SLOPE IN FRONT OF BARRIER • ANY BARRIER ANY PLACE ON 10:1 OR FLATTER SLOPE • CABLE GUARDRAIL ANY PLACE ON 6:1 OR FLATTER (SPECIAL 4:1 FOR PROPRIETARY) • BEAM GUARDRAIL – 6:1 OR FLATTER IF OUTSIDE NO-NO AREA

  9. Roadside Guardrail Location (cont.) • SOIL SUPPORT BEHIND POSTS • USE LONGER POST IF ≤ 1’ OF RELATIVELY FLAT • FLARE RATE

  10. Median Guardrail Location • SAME AS ROADSIDE GUARDRAIL EXCEPT: • CABLE GUARDRAIL IN SWALE – 1’- 8’ NO-NO

  11. Special Considerations • POST DRIVING INTERFERENCE • LEAVE OUT POSTS (NEST RAIL) • EXTRA BLOCKOUTS (ANY POSTS TWO, ONE THREE) • RE-ARRANGE POST SPACING (3’-1 ½ TO 6’-3) • CURVED GUARDRAIL FOR INTERRUPTED LON

  12. Special Considerations (cont.) • CURB EFFECT ON STRONG POST W-BEAM • CURB ≤ 4” = NO SUBSTANTIAL EFFECT • STIFFEN SYSTEM: RUB RAIL, BACK RAIL • NOT REALLY APPLICABLE TO LOW SPEED • GUARDRAIL POSTS IN ROCK • GAPS IN GUARDRAIL – MUST DEVELOP TENSION; TYPICALLY 200’ MIN

  13. Length of Need (LON) LENGTH OF NEED – THE LENGTH OF BARRIER NEEDED IN ADVANCE OF THE HAZARD BASED ON THE STOPPING DISTANCE ONCE A VEHICLE LEAVES THE TRAVELWAY NOT ON ANGLE OF DEPARTURE FIELD CHECK – WALK 15 TIMES THE DISTANCE FROM EOTW TO BACK OF HAZARD AND THEN SIGHT

  14. Transitions • USED WHEN MOVING FROM A SOFTER BARRIER TO A HARDER BARRIER - GRADUALLY • MOST TYPICAL – W-BEAM TO CONCRETE • USE CRASH-TESTED AS CONDITIONS ALLOW • MUST HAVE STRUCTURAL CONNECTION (TENSION) • EXTRA AND/OR LARGER POSTS • NESTED RAIL ELEMENT • SNAGGING PREVENTION – RUB RAIL OR CURB

  15. End Treatments PURPOSE: SHIELD THE END OF THE BARRIER AND DEVELOP TENSION FOR METAL GUARDRAIL SYSTEMS FUNCTION: EITHER CAPTURE OR ALLOW A VEHICLE TO PASS THROUGH FOR END-ON HITS AND REDIRECT ON SIDE HITS – MOST GATE (USE CABLE TO DEVELOP TENSION) HISTORICAL: BLUNT END; TURNDOWN; BCT NOT GENERALLY ALLOWED MUST BE CRASH TESTED – UP TO 7 TESTS AVAILABLE FOR CABLE AND BOX BEAM

  16. End Treatments (cont.) • BURIED-IN-BACKSLOPE –THE BEST SOLUTION • TESTED ON FRONT SLOPE OF 4:1 (NEED RUBRAIL) • FLARE RATE • ANCHORED 1’ UNDER GROUND – STEEL OR CONCRETE • LAST POINT OF EFFECTIVE GUARDRAIL AT TOE OF BACKSLOPE • FOR DOUBLE RAIL, TOP OF RAIL STAYS LEVEL WITH ROADWAY

  17. End Treatments (cont.) • FLARED TERMINALS - NON-ENERGY ABSORBING • SRT - SLOTS TO BUCKLE RAIL ON END-ON HITS • FLARED TERMINALS - ENERGY ABSORBING • FLEAT - FLARE MUST BE ON STRAIGHT LINE • TERMINALS ARE 371/2’ LONG (TL-3) • GENERALLY A 4’ FLARE • REDIRECTION BEGINS AT THIRD POST ONLY USE IF RUNOUT AVAILABLE AND FULL GRADING

  18. End Treatments (cont.) • PARALLEL TERMINALS (SINGLE SIDED) ENERGY ABSORBING; PROPRIETARY • ET (PLUS) – 2000 (EXTRUDER TERMINAL) • SKT (SEQUENTIALLY KINKING TERMINAL) • ENERGY ABSORBING HEADS WORK ON RAIL ELEMENT • TERMINALS ARE 50’ LONG (TL-3) • RECOMMEND OFFSET FIRST POST 1-2’ • MUST BE CONSTRUCTED ON STRAIGHT LINE • REDIRECTION BEGINS AT THIRD POST

  19. End Treatments (cont.) • PARALLEL TERMINALS (DOUBLE SIDED) ENERGY ABSORBING • CAT – CUT METAL BETWEEN HOLES IN RAIL • BRAKEMASTER – BRAKE GRABS ON FIXED CABLE • TERMINALS ARE 30 – 37 1/2’ LONG • BRAKEMASTER SOMEWHAT “HARDIER” • CONSTRUCTED ON STRAIGHT LINE • REDIRECTION BEGINS AT FOURTH POST FOR • CAT AND MIDPOINT FOR BRAKEMASTER

  20. End Treatments (cont.) SITE GRADING REQUIREMENTS • ADVANCE GRADING: 10:1 OR FLATTER ON GRADUAL (15:1) TAPER • ADJACENT GRADING: FLAT 5 FEET BEHIND POST AND 4:1 BEYOND (REDUCED ALTERNATIVE FOR PARALLEL TERMINALS) • LONGITUDINAL RUNOUT DISTANCE GRADING: CLEAR ZONE REPEAT - FLARED TERMINALS NOT APPROPRIATE WITHOUT FULL GRADING

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