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|Description Text||IDOT is currently reviewing our Traffic Barrier Terminal (TBT/AGT) standards to make sure they meet MASH requirements. We had a couple questions we wanted to run by you guys as guidance on a few items which will be described below.
I’ve attached the following documents for your review:
• Our current TBT Type 6 (NCHRP 350)
• Drafted changes to our TBT Type 6
• Permanent Concrete Barrier Design that TBT Type 6 will be attached
Questions we have:
1. Is the curb required or can it be an option?
2. Is the wedge plate required? If so, is our design okay to use?
3. Is the vertical face taper under the connection of the AGT required when there is NOT curb present? (See page 2)
4. Is the vertical face taper under the connection of the AGT required when there is a curb present? (See page 2)
5. Can we use 3’- 1 ½” spacing for the first 10 post instead of the 1’-6 ¾” spacing?
6. Block out widths for post 1 – 11 can be either 12”, 8” or either?
7. Block out material can be wood or composite for entire run?
8. Would the height have to be at 34” tall to match the proposed AGT design for the steel railing you guys are developing for us if we want to be consistent?
Please let me know if you have any questions or need any additional information from us. We look forward to discussion these changes and any recommendations you guys may have for us. Thank you!
|Date||August 31, 2018|
|Attachment||Detail_conc barrier dblface 44in (replaces Std 637006).pdf|
|Attachment||Traffic Barrier Terminal Type 6 Current Standard_NCHRP 350.pdf|
|Attachment||Traffic Barrier Terminal Type 6_MASH_updates_8_31_2018.pdf|
I have responses to your questions below in in the same order as numbered in your email. However, before we get too far into the AGT design, I want to remind you of the standardized transition buttress that was recently designed here at MwRSF. This buttress has been evaluated to MASH and is compatible with a variety of transitions, curbs, and adjacent concrete barrier configurations. We highly recommend utilizing the standardized buttress in your approach transitions in the future. I have attached a TRR Journal paper to this email that explains the design and some implementation issues.
Questions (and answers):
Please review these comments, attached paper, and the MGS stiffness transition report and let me know if you have further questions.
|Date||August 31, 2018|
130 Whittier Research Center
2200 Vine Street
Lincoln, NE 68583-0853
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