KDOT Guardrail, Barriers & Safety Appurtenances 2 — Questions and Answers
Question 1: What is the primary purpose of a crash cushion (attenuator) placed at the nose of a concrete barrier or rigid fixed hazard?
- To increase the visual profile of the hazard for drivers
- To redirect vehicles parallel to the hazard
- To absorb impact energy and decelerate a vehicle safely (Correct answer)
- To provide a rumble-strip warning for approaching traffic
Correct answer: To absorb impact energy and decelerate a vehicle safely
Crash cushions (attenuators) absorb the kinetic energy of an impacting vehicle to decelerate it safely, protecting both vehicle occupants and the fixed hazard behind the device.
Question 2: What is the standard length of a single W-beam guardrail panel?
- 6 feet 3 inches
- 12 feet 6 inches (Correct answer)
- 25 feet
- 50 feet
Correct answer: 12 feet 6 inches
Standard W-beam guardrail panels are 12 feet 6 inches (150 inches) in length, allowing them to span two standard post spacings with appropriate splice overlap at each post.
Question 3: When temporary concrete barrier (TCB) is used as a work zone divider on a KDOT project, what connection requirement applies at every joint?
- Joints are left open to allow water drainage
- Every joint must be pinned to prevent barrier separation during an impact (Correct answer)
- Only the end barriers at each run require pinning
- Pinning is required only during nighttime work hours
Correct answer: Every joint must be pinned to prevent barrier separation during an impact
KDOT requires all temporary concrete barrier joints to be pinned to prevent individual segments from separating during an impact, which could allow an errant vehicle to penetrate the work zone.
Question 4: What corrosion protection standard typically applies to guardrail hardware (bolts, nuts, and washers) on KDOT projects?
- ASTM A325 high-strength bolts without coating
- Hot-dip galvanizing per ASTM A153 or equivalent (Correct answer)
- Two coats of rust-inhibiting primer paint
- Stainless steel is the only acceptable material
Correct answer: Hot-dip galvanizing per ASTM A153 or equivalent
Guardrail hardware must be hot-dip galvanized per ASTM A153 or the applicable KDOT specification to provide corrosion resistance for the full service life of the installation.
Question 5: What is the purpose of a guardrail flare at a terminal location?
- To increase retroreflectivity of the guardrail end section
- To gradually transition the rail away from the traveled way to reduce the probability of an end-on impact (Correct answer)
- To connect the terminal directly to a bridge deck parapet
- To mark the end of a construction zone for approaching drivers
Correct answer: To gradually transition the rail away from the traveled way to reduce the probability of an end-on impact
A guardrail flare gradually moves the terminal away from the traveled way, reducing the likelihood that a vehicle will strike the end head-on and improving overall safety performance.
Question 6: Who must approve any substitution of a non-standard or alternate guardrail end terminal on a KDOT project?
- The prime contractor's foreman
- The KDOT project engineer (Correct answer)
- The guardrail subcontractor's project manager
- The county engineer for projects on county roads
Correct answer: The KDOT project engineer
Any substitution of non-standard guardrail hardware requires approval from the KDOT project engineer, who holds authority over construction acceptance and must verify the substitute meets safety requirements.
Question 7: What characteristic of the New Jersey (NJ) profile concrete barrier makes it effective in work zone and median applications?
- Its ability to be repositioned by a single worker
- Its sloped lower face that redirects vehicle tires upward to reduce snagging and vaulting (Correct answer)
- Its built-in compatibility with thrie-beam rail transitions
- Its lower cost compared to W-beam guardrail installations
Correct answer: Its sloped lower face that redirects vehicle tires upward to reduce snagging and vaulting
The NJ profile features a sloped lower face designed to redirect vehicle tires upward during impact, reducing undercarriage snagging and preventing vehicles from vaulting over the barrier.
KDOT Guardrail, Barriers & Safety Appurtenances 2
What is the primary purpose of a crash cushion (attenuator) placed at the nose of a concrete barrier or rigid fixed hazard?