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

APPENDIX A. ADDITIONAL INSTALLATION DETAILS FROM ILLINOIS

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

Cable Median Barriers and Shoulder Rumble Strip Combination Questions—Illinois

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:

     Standard 642001-02 → Shoulder rumble strip 16 inches, and

     Standard 642006 → Shoulder rumble strip 8 inches.

     http://www.idot.illinois.gov/Assets/uploads/files/Doing-Business/Standards/Highway-Standards/HighwaysStandardsRevision215.pdf.

     Specifications → Section 642 Shoulder Rumble Strip (p. 554–555).

     http://www.idot.illinois.gov/Assets/uploads/files/Doing-Business/Manuals-Guides-&-Handbooks/Highways/Construction/Standard-Specifications/12SpecBook.pdf.

     Bureau of Design and Environment Manual → CH 34 Section 34-2.02(e) Rumble strip (p. 15–16).

     http://www.idot.illinois.gov/Assets/uploads/files/Doing-Business/Manuals-Split/Design-And-Environment/BDE-Manual/Chapter%2034%20Cross%20Section%20Elements.pdf

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

     Answer:

     Bureau of Design and Environment Manual → CH 38-7, Median barriers

     http://www.idot.illinois.gov/Assets/uploads/files/Doing-Business/Manuals-Split/Design-And-Environment/BDE-Manual/Chapter%2038%20Roadside%20Safety.pdf

     Supplemental Specification for Section 644 High Tension Cable Median Barriers (p. 58–59)

     http://www.idot.illinois.gov/Assets/uploads/files/Doing-Business/Manuals-Guides-&-Handbooks/Highways/Construction/Supplemental-Standards-Specifications/2015Supp.pdf

     Approved list of High Tension Cable Median Barriers

     http://idot.illinois.gov/Assets/uploads/files/Doing-Business/Specialty-Lists/Highways/Materials/Materials-&-Physical-Research/Metals/htcmedianbarrier.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 barriers at the study sites?

   Answer: Cable median barrier was installed at these locations to reduce cross-median crashes. This was based on an examination of 5 years of crash data. Illinois used FARS crashes on interstates and looked at head on and opposite-direction sideswipe. They used this information to develop a warrant chart [and] a subsequent list of sites for cable median barrier installation. For cable median barrier, the median width had to be no more than 100 ft.

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

   Answer: Variable.

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

   Answer: Supervision required for both rumble strip and cable median barrier contractor was pretty extensive. Constant checking for uniformity was required to meet required specification.

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

   Answer: Ongoing maintenance is maybe more than originally projected in some Districts due to the number of cable barrier hits. Since cable barrier is doing its job, monthly repairs are not uncommon and should be expected/budgeted.

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

   Answer: Both low cost safety improvements appear to be a good investment in saving lives on roads.