KDOT Guardrail, Barriers & Safety Appurtenances 1 — Questions and Answers
Question 1: What is the standard height of W-beam guardrail from finished grade to the top of the rail?
- 24 inches
- 27¾ inches (Correct answer)
- 31 inches
- 36 inches
Correct answer: 27¾ inches
AASHTO and KDOT standards specify W-beam guardrail top height at 27¾ inches from finished grade for effective vehicle redirection.
Question 2: Which crash test manual currently governs acceptance of roadside safety hardware on KDOT projects?
- NCHRP Report 350
- AASHTO MASH (Correct answer)
- FHWA Circular No. 5040.8
- MUTCD Chapter 6
Correct answer: AASHTO MASH
The Manual for Assessing Safety Hardware (MASH) has replaced NCHRP 350 as the required crash test standard for roadside safety hardware on federal-aid projects including KDOT work.
Question 3: When inspecting guardrail post installation, what must be verified about posts driven into soil?
- Post depth must equal post height above ground
- Posts must be set plumb and at the correct embedment depth per plans (Correct answer)
- Posts must be filled with concrete grout
- Posts must be painted safety yellow for visibility
Correct answer: Posts must be set plumb and at the correct embedment depth per plans
Guardrail posts must be installed plumb and at the specified embedment depth per KDOT plans to ensure the system performs as designed during an impact event.
Question 4: What type of end treatment is required at the approach end of a guardrail run where traffic may directly impact the terminal?
- Blunt end with retroreflector
- Turned-down end anchored to the ground
- MASH-compliant flared terminal (Correct answer)
- Concrete anchor block only
Correct answer: MASH-compliant flared terminal
Approach ends of guardrail must be equipped with MASH-compliant flared terminals to safely redirect or absorb impacting vehicles rather than creating a spear-like hazard.
Question 5: What is the standard post spacing for W-beam strong-post guardrail systems?
- 3 feet 1½ inches
- 6 feet 3 inches (Correct answer)
- 10 feet
- 12 feet 6 inches
Correct answer: 6 feet 3 inches
The standard post spacing for strong-post W-beam guardrail is 6 feet 3 inches (75 inches) center to center as specified in AASHTO guidelines adopted by KDOT.
Question 6: During guardrail installation inspection, which splice orientation defect requires immediate correction?
- Rail sections showing minor surface rust at the splice
- Rail sections lapped in the wrong direction relative to traffic flow (Correct answer)
- Splice bolts that are slightly overtightened
- Rail stored on wooden pallets before installation
Correct answer: Rail sections lapped in the wrong direction relative to traffic flow
W-beam rail sections must be lapped with the downstream end overlapping the upstream end so that a vehicle impact cannot catch the splice edge and peel the rail away from the posts.
Question 7: What is the purpose of the offset block (blockout) used between the W-beam rail and the guardrail post?
- To increase the decorative appearance of the guardrail
- To move the rail face away from the post and allow the system to deflect properly during impact (Correct answer)
- To reduce the installed height of the rail to AASHTO standards
- To provide electrical insulation between the post and rail
Correct answer: To move the rail face away from the post and allow the system to deflect properly during impact
Offset blocks (blockouts) hold the W-beam rail away from the post face, creating space needed for the system to deflect and absorb energy during a vehicle impact.
KDOT Guardrail, Barriers & Safety Appurtenances 1
What is the standard height of W-beam guardrail from finished grade to the top of the rail?