Safety Evaluation of Cable Median Barriers in Combination With Rumble Strips on Divided Roads

APPENDIX B. ADDITIONAL INSTALLATION DETAILS FROM KENTUCKY

This appendix presents further details about the cable barrier installations from Kentucky based on a questionnaire that was sent to the participating States.

Cable Median Barriers and Shoulder Rumble Strip Combination Questions—Kentucky

1. What was the “before-period” condition for the treatment sites with respect to rumble strips and cable median barriers?
   • No cable median barriers and no rumble strips.
   • Cable median barriers present but no rumble strips.
   • No cable median barriers but rumble strips present.

     Answer: No cable median barriers but rumble strips present.

2. What type(s) of rumble strips were characteristic of the treatment sites evaluated by this study? (Check all that apply.)
   • Milled.
   • Rolled.
   • Formed.
   • Raised.
   • Other.

     Answer: Milled and rolled.

3. Can you provide specifications and/or standard drawings that address the following characteristics of the rumble strips evaluated by this study?
   • Width.
   • Length.
   • Depth.
   • Spacing.
   • Lateral placement (i.e., in relation to pavement marking).

     Answer:
     http://transportation.ky.gov/Construction/Standard%20amd%20Supplemental%20Specifications/400%20Asphalt%20Pavements%2012.pdf.

     Section 403.03.08

4. Can you provide specifications and/or standard drawings that address the following characteristics of the cable median barriers evaluated by this study?
   • Number of cables.
   • Post spacing.
   • Other important design considerations (i.e., cable pre-stretch, tensioning, slope placement, footing design).

     Answer:
     http://transportation.ky.gov/Construction-Procurement/Proposals/201-CHRISTIAN-MARSHALL-MCCRACKEN-141230.pdf.

5. What were the requirements (e.g., minimum paved shoulder width, minimum median width, number of lanes, etc.) for the installation of rumble strips and cable median barrier at the study sites?

   Answer: Cable installations are generally selected based on an annual evaluation process that considers crash experience, median width, median slope profile, traffic volume, traffic composition, and speed. From these variables, KYTC prioritizes a list of recommended cable barrier projects. Median width had to be narrower than 200 ft.

6. What was the lateral offset from the road to the cable median barriers and how was that distance selected?

   Answer: Approximately 8 ft lateral offset from travel lanes based on deflection on 10 ft post spacing.

7. Please describe any challenges related to the rumble strip and/or cable median barrier installation and how you overcame them.

   Answer: Monitor depth and alignment of rumbles. Ensure proper anchor placement for appropriate median coverage near bridges and coordinate minimum/maximum “gap” spacing for emergency vehicles.

8. Please describe any challenges related to the rumble strip and/or cable median barrier maintenance and how you overcame them.

   Answer: Cable barrier maintenance is handled through contract. No substantial issues with maintenance of rumbles.

9. What lessons learned or recommendations would you share with another state interested in the widespread application of cable median barriers and rumble strips?

   Answer: Have a defendable program to evaluate and select installations.