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We've had several meetings within Mn/DOT to discuss various options and criteria regarding traffic barriers on bridges and barrier/guardrail transitions and would like to have a conference call w/ either or both of you to get your opinions and insights on these issues (see specific details below). We're proposing a 2 hour telephone or video conference call the week of March 7^th or 14^th.

Could you please respond by indicating 2-3 times/dates that work for you? Do you have video conference capabilities?

Specific issues we'd like to discuss are outline below;

1). Our past/present policy is to place traffic barriers on bridges "plumb" or "level", regardless of the adjacent shoulder slope. (See Figure 1.jpg);

Any comment on this? Do you know if other states use a similar detail?

2). Our current policy on when to use a TL-5 barrier (42" high) on a bridge (in lieu of a TL-4, 32" high) includes the following criteria; Degree of curvature > 5 degrees (radius of 1145 ft) and speed > 40 mph. An incomplete survey of nearby states indicates they use the following TL-5 criteria;

Illinois

a). Structures with a future DHV (one way) x % trucks greater than 250

b). Structures located in areas with high incidences of truck rollover accidents.

c). Structures with a radius of 1000 ft. or less with truck traffic

Nebraska

All interstate structures, expressways, and over railroads.

They use a 34" (2" taller than Mn/DOT) TL-4 barrier on all other "on system" bridges.

Iowa

"Most interstate projects due to higher truck traffic"

Michigan/North Dakota/South Dakota

No set policy for use of TL-5 barrier.

Any guidance, criteria, or opinions on when to use TL-5 barriers on bridges?

3). At the end of a concrete barrier, where it transitions to a guardrail connection, Mn/DOT details a slight slope (5V:12H) to the top of the barrier (see top sketch below).
This guardrail connection/transition has been crash tested and approved for TL-3. What is the appropriate slope or taper length that should be used when transitioning from a 42" (or taller, glare screen barrier that is 4'6" tall, 6V:12H taper) barrier to a guardrail connection? (See Figure 2.jpg and Figure 3.jpg)

4). Based on recent test results regarding the New Jersey shape and the new MASH criteria do you have any recommendations or considerations for what shape and height of barrier should be used on new bridges going forward? We're considering single slope, vertical face, etc, and looking for advice. Which states (if any) do feel are headed in the right direction and may have standards that we can review and compare? FYI, our version of a vertical face bridge
barrier is shown in Figure 4.jpg.

MnDOT had a conference call with MwRSF to discuss various questions regarding barriers on superelevations and cross slopes. A summary of the discussion is attached.