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MASH TBR guidance

Question
State	IA
Description Text	With the publishing of recent TBR-related report TRP-03-337-17, I’m trying to combine available MASH TBR guidance into one place and would appreciate a review by MwRSF to confirm this is the current guidance. I’ve attached schematics that incorporate my understanding discussed below and have included applicable pages numbers. Full impact condition where TBR is adjacent to severe drop-off or missing bridge rail (pages 1, 2, 3, and 4) Minimum of five segments of TBR on the approach, which may include flaring from tangent to 6:1 (62.5’) Design-specific number of segments protecting the work area, where work/equipment storage/etc. may begin 80” from back of TBR Minimum of seven segments of TBR on the trailing end, which may include flaring from tangent to 6:1 (87.5’) For two-way protection, both the approach and trailing will be a minimum of seven segments (87.5’) Notes: Iowa has decided that a severe drop-off is any longitudinal opening greater than 36” that is at least 3” deep. The 36” value attempts to mimic cross-drain pipe guidance under Section 3.4.2.1 Traversable Designs of the 2011 Roadside Design Guide. Iowa has decided that the deflection noted for Region A and Region C (132”) will be treated as “unlimited” deflection, thus extending the approach (originally three) and trailing (originally five) sections by two sections. The 132” value comes from TRP-03-337-17, top of page 148 and Figure 113 on page 154. The 80” value comes from TRP-03-337-17, top of page 154 and Figure 113 on page 154. Iowa currently has the 80” value as 45” based on NCHRP 350 testing from TRP-03-113-03, top of page 14 and originally from TRP-03-64-96 bottom of page 45. Five segments on approach end from TRP-03-337-17, Figure 113 on page 154 and Figure 114 on page 155. Seven segments on trailing end from TRP-03-337-17, Figure 113 on page 154 and Figure 114 on page 155. Five and seven segments were previously eight segments (100’) from TRP-03-209-09, middle of page 6. 85^th percentile impact condition for all other conditions (pages 1, 2, 3, and 4) Minimum of five segments of TBR on the approach, which may include flaring from tangent to 6:1 (62.5’) Design-specific number of segments protecting the work area, where work/equipment storage/etc. may begin 68” from back of TBR Minimum of seven segments of TBR on the railing end, which may include flaring from tangent to 6:1 (87.5’) For two-way protection, both the approach and trailing will be a minimum of seven segments (87.5’) Notes: Iowa has decided that the deflection noted for Region A and Region C (97”) of TRP-03-337-17 will be treated as “unlimited” deflection, thus extending the approach (originally three) and trailing (originally five) sections by two sections. The 97” value comes from TRP-03-337-17, bottom of page 150 and Figure 114 on page 155. The 68” value comes from TRP-03-337-17, top of page 154 and Figure 114 on page 155 Iowa currently has the 68” value as 24” based on NCHRP 350 testing from TRP-03-113-03, top of page 14. Five segments on approach end from TRP-03-337-17, Figure 113 on page 154 and Figure 114 on page 155. Seven segments on trailing end from TRP-03-337-17, Figure 113 on page 154 and Figure 114 on page 155. Five and seven segments were previously eight segments (100’) from TRP-03-209-09, middle of page 6. Active testing to reduce deflection Through additional testing and redesign, there appears to be a chance for the full impact and 85^th percentile deflections to be brought down from 80” and 68” to 41“ and 24” using steel tubes, but that design is still under refinement and an end transition has yet to be developed. Notes: The 41” value comes from TRP-03-295-14, bottom of page 247. The 24” value comes from TRP-03-295-14, bottom of page 248. Anchoring (pages 3, 4, 5, 6, and 8) In cases where the combined lateral space requirement for barrier deflection and needed work area cannot be met, the barrier will need to be anchored. Anchoring the barrier will reduce the deflection down to 6” for both impact conditions. Notes: The 6” value comes from TRP-03-180-06, middle of page 89. Anchor Transitions (pages 3 and 4) In cases where only parts of an installation need to be anchored, an anchor transition can be incorporated. This transition takes places over four segments with 1, 2, 3, and 3 anchors on the traffic side, both sides if used as a traffic separator, approaching fully anchored TBR, permanent barrier, or bridge rail. This anchor transition will also apply to certain crash cushions depending on their anchoring mechanism. Notes: Four anchor transition sections from TRP-03-208-10, Figure 4 on page 15. Deflections between anchored sections (pages 3, 4, and 7 but specifically page 9) One point of discussion that has risen from this is the expected deflection of unanchored TBR between two sections of anchored TBR. This might occur on bridge maintenance projects where the area of concern is only a couple feet longitudinally (replacing a joint for example), but there may be multiple areas of concern along the bridge. In an attempt to avoid anchoring the entire run of barrier, what deflections should be used within the unanchored portions? Your assistance in the matter is greatly appreciated. Since this is a lot to digest, if you feel discussion would be better served with a review followed by a conference call, we’d be more than welcoming.

Question

State

Description Text

With the
publishing of recent TBR-related report TRP-03-337-17, I’m trying to combine
available MASH TBR guidance into one place and would appreciate a review by
MwRSF to confirm this is the current guidance. I’ve attached schematics that
incorporate my understanding discussed below and have included applicable pages
numbers.

Full impact
condition where TBR is adjacent to severe drop-off or missing bridge rail
(pages 1, 2, 3, and 4)

Minimum of five segments of TBR on the approach, which may
include flaring from tangent to 6:1 (62.5’)

Design-specific number of segments protecting the work area,
where work/equipment storage/etc. may begin 80” from back of TBR

Minimum of seven segments of TBR on the trailing end, which may
include flaring from tangent to 6:1 (87.5’)

For two-way protection, both the approach and trailing will be a
minimum of seven segments (87.5’)

Notes:

Iowa has decided that a
severe drop-off is any longitudinal opening greater than 36” that is at
least 3” deep. The 36” value attempts to mimic cross-drain pipe guidance
under Section 3.4.2.1 Traversable Designs of the 2011 Roadside Design
Guide.

Iowa has decided that the
deflection noted for Region A and Region C (132”) will be treated as
“unlimited” deflection, thus extending the approach (originally three) and
trailing (originally five) sections by two sections. The 132” value comes
from TRP-03-337-17, top of page 148 and Figure 113 on page 154.

The 80” value comes from TRP-03-337-17, top of page 154 and Figure 113 on page 154.

Iowa currently has the 80”
value as 45” based on NCHRP 350 testing from TRP-03-113-03, top of page 14 and originally from TRP-03-64-96 bottom of page 45.

Five segments on approach
end from TRP-03-337-17, Figure 113 on page 154 and Figure 114 on page
155.

Seven segments on trailing
end from TRP-03-337-17, Figure 113 on page 154 and Figure 114 on page
155.

Five and seven segments
were previously eight segments (100’) from TRP-03-209-09, middle of page 6.

85^th
percentile impact condition for all other conditions (pages 1, 2, 3, and 4)

Minimum of five segments of TBR on the approach, which may
include flaring from tangent to 6:1 (62.5’)

Design-specific number of segments protecting the work area,
where work/equipment storage/etc. may begin 68” from back of TBR

Minimum of seven segments of TBR on the railing end, which may
include flaring from tangent to 6:1 (87.5’)

For two-way protection, both the approach and trailing will be a
minimum of seven segments (87.5’)

Notes:

Iowa has decided that the
deflection noted for Region A and Region C (97”) of TRP-03-337-17 will be treated as “unlimited” deflection, thus
extending the approach (originally three) and trailing (originally five)
sections by two sections. The 97” value comes from TRP-03-337-17, bottom of page 150 and Figure 114 on page 155.

The 68” value comes from TRP-03-337-17, top of page 154 and Figure 114 on page 155

Iowa currently has the 68”
value as 24” based on NCHRP 350 testing from TRP-03-113-03, top of page 14.

Five segments on approach
end from TRP-03-337-17, Figure 113 on page 154 and Figure 114 on page
155.

Seven segments on trailing
end from TRP-03-337-17, Figure 113 on page 154 and Figure 114 on page
155.

Five and seven segments
were previously eight segments (100’) from TRP-03-209-09, middle of page 6.

Active
testing to reduce deflection

Through additional testing and redesign, there appears to be a
chance for the full impact and 85^th percentile deflections to be
brought down from 80” and 68” to 41“ and 24” using steel tubes, but that design
is still under refinement and an end transition has yet to be developed.

Notes:

The 41” value comes from TRP-03-295-14, bottom of page 247.

The 24” value comes from TRP-03-295-14, bottom of page 248.

Anchoring
(pages 3, 4, 5, 6, and 8)

In cases where the combined lateral space requirement for
barrier deflection and needed work area cannot be met, the barrier will need to
be anchored. Anchoring the barrier will reduce the deflection down to 6” for
both impact conditions.

Notes:

The 6” value comes from TRP-03-180-06, middle of page 89.

Anchor
Transitions (pages 3 and 4)

In cases where only parts of an installation need to be
anchored, an anchor transition can be incorporated. This transition takes
places over four segments with 1, 2, 3, and 3 anchors on the traffic side, both
sides if used as a traffic separator, approaching fully anchored TBR, permanent
barrier, or bridge rail. This anchor transition will also apply to certain
crash cushions depending on their anchoring mechanism.

Notes:

Four anchor transition
sections from TRP-03-208-10,
Figure 4 on page 15.

Deflections
between anchored sections (pages 3, 4, and 7 but specifically page 9)

One point of
discussion that has risen from this is the expected deflection of unanchored TBR
between two sections of anchored TBR. This might occur on bridge maintenance
projects where the area of concern is only a couple feet longitudinally
(replacing a joint for example), but there may be multiple areas of concern
along the bridge. In an attempt to avoid anchoring the entire run of barrier,
what deflections should be used within the unanchored portions?

Your assistance
in the matter is greatly appreciated. Since this is a lot to digest, if you
feel discussion would be better served with a review followed by a conference
call, we’d be more than welcoming.

System Performance Evaluation

System Types
Portable Barriers

Applications

System Features

Date August 11, 2017
Previous Views (168) Favorites (0)

Attachment TBR layouts.pdf

Response
Response (active)	I have reviewed the information you sent and have some comments. In general, the details look good. I have commented below in red in the appropriate sections and have some separate comments as well regarding the layout diagrams that accompanied the email. On the diagram for ROADSIDE APPLICATION – ANCHOR TRANSITION – OPPOSING TRAFFIC NOT WITHIN CLEAR ZONE, there may be potential to reduce or taper the deflection area in the transition region. We know from previous testing that the deflection in the region of pinned barriers is significantly less than a free-standing PCB. On the diagram for ROADSIDE APPLICATION – ANCHORED– OPPOSING TRAFFIC NOT WITHIN CLEAR ZONE, I should note that we have never analyzed or tested the use of the pinned transition for anchorage of the end of the PCBs. While there is potential for this to work, there may be further study warranted. Unfortunately, the has not been much in terms of other solutions that have been proposed. The development and evaluation of guidance for this area was noted as a research need in the PCB LON study recommendations. We did develop a MASH TL-3 upstream anchorage that you may wish to consider. http://mwrsf.unl.edu/researchhub/files/Report63/TRP-03-209-09.pdf A similar comment would apply to the use of the transition as a downstream anchor on several of the layouts. However, as I noted, there may not be a better alternative at this time… On the diagram for MEDIAN APPLICATION – ANCHORED–TRAFFIC SEPARATOR, the use of barriers pinned on both sides for deflection reduction has not been tested to NCHRP 350 or MASH. There have been concerns in the past that doing so may increase the potential for tipping of the barrier which leads to increased vehicle climb and instability. CALTRANS testes their K-rail segment in this configuration under NCHRP 350 and the results were not encouraging in terms of vehicle stability. This type of installation may potential work and there may not be a better alternative. However, further research is likely warranted. I believe we have noted this in previous Pooled Fund position papers and some states have shown interest. It was never funded. You had also replied with the following: However, I’m beginning to wonder if this should be discussed as a conference call amongst the pooled fund instead. I think a lot of states will have TBR-related questions and there isn’t a reason for you to answer it sixteen different times. I know Kansas has already asked and I doubt we’ll be the last ones. This would buy you a little more time and would (selfishly) help us know what the other DOT’s intentions are. Is everyone adopting the larger deflections? Is everyone moving to the tubed rail? Any interest in in-service evaluations of current deflections? I think this would be a great group discussion such that we all proceed as a complete group rather than sixteen different entities. While I do see the value of getting all of the states on the same page, I am a little reluctant to turn this into a group wide discussion due to the fact that each state tends to have different concerns or preferences on these items. In addition, MwRSF does not typically wish to dictate hardware policies to states, and in many cases, states don’t want us to. That is generally better served by the RDG. As such, the discussion you are proposing would need to be more of a discussion of your proposed guidance and MwRSF could provide input and recommendations. I will be putting this on the consulting web site to help distribute it unless that is an issue for you. If you really feel the desire to have that discussion with the group, I can try to set something up. I don’t know how many states are implementing the reduced deflection system we did for WisDOT. Currently, the transition between that system and the free-standing PCB needs to be completed, so I don’t believe it has been widely adapted. I do believe that several states are working towards implementing the larger barrier deflections as part of the MASH implementation efforts. I also believe this has caused some stress, and this has led to the development of an NCHRP problem statement to develop a MASH TL-3 PCB. We have proposed something similar in the Pooled Fund for several years, but it has not moved to the forefront. In-service evaluation of work zone devices has been limited, but it would be interesting. I know that a study of work zone encroachments has been proposed several times but has not received funding. Let me know what you think. Thanks _____________________________________ Good morning! With the publishing of recent TBR-related report TRP-03-337-17, I’m trying to combine available MASH TBR guidance into one place and would appreciate a review by MwRSF to confirm this is the current guidance. I’ve attached schematics that incorporate my understanding discussed below and have included applicable pages numbers. Full impact condition where TBR is adjacent to severe drop-off or missing bridge rail (pages 1, 2, 3, and 4) Minimum of five segments of TBR on the approach, which may include flaring from tangent to 6:1 (62.5’) Just a reminder that 6:1 flares were never crash tested or evaluated. This was a recommendation from NCHRP 358. Additionally, flaring of the barriers outside of the LON may reduce their effectiveness in providing barrier tension in the LON, which would result in potentially larger barrier deflections. However, the research in TRP-03-337-17 required only 3 barrier segments in that region. As you have included an additional two barrier segments, this concern is much less. Design-specific number of segments protecting the work area, where work/equipment storage/etc. may begin 80” from back of TBR Minimum of seven segments of TBR on the trailing end, which may include flaring from tangent to 6:1 (87.5’) For two-way protection, both the approach and trailing will be a minimum of seven segments (87.5’) Notes: Iowa has decided that a severe drop-off is any longitudinal opening greater than 36” that is at least 3” deep. The 36” value attempts to mimic cross-drain pipe guidance under Section 3.4.2.1 Traversable Designs of the 2011 Roadside Design Guide. There is no hard data on vertical drop severity in terms of full-scale testing. Several studies have looked at cost benefit ratios of vertical drops based on ADT. I have attached two studies done at TTI. They may provide additional guidance on what level of vertical drop would be acceptable. Additionally, I should note that the 36” lateral opening you note above was based on research and testing of culvert pipes at TTI. Those evaluations were based on a vehicle traversing 36” pipes. If a vehicle attempts to traverse a similar lateral gap at an angle, the actual distance it must traverse becomes greater. Thus, there may be a need to lower 36” gap size. Iowa has decided that the deflection noted for Region A and Region C (132”) will be treated as “unlimited” deflection, thus extending the approach (originally three) and trailing (originally five) sections by two sections. The 132” value comes from TRP-03-337-17, top of page 148 and Figure 113 on page 154. The 80” value comes from TRP-03-337-17, top of page 154 and Figure 113 on page 154. The deflection for barrier segments AS1 and AS2 in your “ROADSIDE APPLICATION – UNANCHORED – OPPOSING TRAFFIC NOT WITHIN CLEAR ZONE” detail may be slightly higher than the 80” value listed due to their proximity to the upstream end of the PCB system. Because these barriers are within 7 barriers of the end of the system, the deflection may be closer to the 91” deflection shown for a 14 barrier system in Figure 110 and 113. Iowa currently has the 80” value as 45” based on NCHRP 350 testing from TRP-03-113-03, top of page 14 and originally from TRP-03-64-96 bottom of page 45. Five segments on approach end from TRP-03-337-17, Figure 113 on page 154 and Figure 114 on page 155. Seven segments on trailing end from TRP-03-337-17, Figure 113 on page 154 and Figure 114 on page 155. Five and seven segments were previously eight segments (100’) from TRP-03-209-09, middle of page 6. 85^th percentile impact condition for all other conditions (pages 1, 2, 3, and 4) Minimum of five segments of TBR on the approach, which may include flaring from tangent to 6:1 (62.5’) Design-specific number of segments protecting the work area, where work/equipment storage/etc. may begin 68” from back of TBR Minimum of seven segments of TBR on the railing end, which may include flaring from tangent to 6:1 (87.5’) For two-way protection, both the approach and trailing will be a minimum of seven segments (87.5’) Notes: Iowa has decided that the deflection noted for Region A and Region C (97”) of TRP-03-337-17 will be treated as “unlimited” deflection, thus extending the approach (originally three) and trailing (originally five) sections by two sections. The 97” value comes from TRP-03-337-17, bottom of page 150 and Figure 114 on page 155. The 68” value comes from TRP-03-337-17, top of page 154 and Figure 114 on page 155 Iowa currently has the 68” value as 24” based on NCHRP 350 testing from TRP-03-113-03, top of page 14. Five segments on approach end from TRP-03-337-17, Figure 113 on page 154 and Figure 114 on page 155. Seven segments on trailing end from TRP-03-337-17, Figure 113 on page 154 and Figure 114 on page 155. Five and seven segments were previously eight segments (100’) from TRP-03-209-09, middle of page 6. Active testing to reduce deflection Through additional testing and redesign, there appears to be a chance for the full impact and 85^th percentile deflections to be brought down from 80” and 68” to 41“ and 24” using steel tubes, but that design is still under refinement and an end transition has yet to be developed. Notes: The 41” value comes from TRP-03-295-14, bottom of page 247. The 24” value comes from TRP-03-295-14, bottom of page 248. Anchoring (pages 3, 4, 5, 6, and 8) In cases where the combined lateral space requirement for barrier deflection and needed work area cannot be met, the barrier will need to be anchored. Anchoring the barrier will reduce the deflection down to 6” for both impact conditions. Anchoring the barrier will not bring the barrier deflection down to 6”. The 6” number refers to the edge distance from the back of the barrier to the drop-off that was tested. From page 89, “The asphalt tie-down system for use with F-shape temporary concrete barriers was tested with a clear gap of 152 mm (6 in.) between the back side of the barriers and the edge of the vertical drop-off. Therefore, this distance is recommended as the minimum safe distance that the barrier system should be installed from the edge of the asphalt roadway. This 152-mm (6-in.) distance from the back side of the barrier does not reflect the distance for safe installation of the tie-down system adjacent to a rigid hazard. For this type of installation, designers must consider the working width of the system obtained during the full-scale testing.” The 6” number also refers to the asphalt pin tie down. The concrete bolted tie-down uses an edge offset of 1”. This system was recently tested to MASH and was successful (Working width = 36.75”, dynamic deflection = 14.25”, static deflection = 8.25”). The asphalt pin testing to MASH is in que. Notes: The 6” value comes from TRP-03-180-06, middle of page 89. Anchor Transitions (pages 3 and 4) In cases where only parts of an installation need to be anchored, an anchor transition can be incorporated. This transition takes places over four segments with 1, 2, 3, and 3 anchors on the traffic side, both sides if used as a traffic separator, approaching fully anchored TBR, permanent barrier, or bridge rail. This anchor transition will also apply to certain crash cushions depending on their anchoring mechanism. I should note here that the transitions we have developed were never evaluated with crash cushion systems. There may be potential for them to work with the crash cushions, but snag and load transfer to the crash cushion have not been evaluated. As you note, some designs may have better performance than others. Notes: Four anchor transition sections from TRP-03-208-10, Figure 4 on page 15. Deflections between anchored sections (pages 3, 4, and 7 but specifically page 9) One point of discussion that has risen from this is the expected deflection of unanchored TBR between two sections of anchored TBR. This might occur on bridge maintenance projects where the area of concern is only a couple feet longitudinally (replacing a joint for example), but there may be multiple areas of concern along the bridge. In an attempt to avoid anchoring the entire run of barrier, what deflections should be used within the unanchored portions? The value of the deflection between anchored sections has never been defined, it would depend on the length and proximity of the unanchored PCBs to the anchored segments. In TRP-03-208-10, we impacted the upstream end of the transition from free-standing PCB’s to concrete median barrier at a location approximately 1 m upstream of the downstream end of the first unanchored barrier segment (barrier no. 5 in that test). The dynamic deflections in that MASH TL-3 test was 44.3 in. at the upstream end of barrier no. 5. Thus, this would be a conservative starting point. As an impact was moved farther from the anchored sections we would expect the deflections to increase to the free-standing PCB deflection of 80”. I think it would be reasonable to assume that that increase in deflection occurs over 3-4 barrier segments. This has not been formally analyzed, but it is likely the best answer I have without further analysis. Your assistance in the matter is greatly appreciated. Since this is a lot to digest, if you feel discussion would be better served with a review followed by a conference call, we’d be more than welcoming.

Response

Response
(active)

I have reviewed the information you sent and have some comments. In general, the details look good.

I have commented below in red in the appropriate sections and have some separate comments as well regarding the layout diagrams that accompanied the email.

On the diagram for ROADSIDE APPLICATION – ANCHOR TRANSITION – OPPOSING TRAFFIC NOT WITHIN CLEAR ZONE, there may be potential to reduce or taper the deflection area in the transition region. We know from previous testing that the deflection in the region of pinned barriers is significantly less than a free-standing PCB.
On the diagram for ROADSIDE APPLICATION – ANCHORED– OPPOSING TRAFFIC NOT WITHIN CLEAR ZONE, I should note that we have never analyzed or tested the use of the pinned transition for anchorage of the end of the PCBs. While there is potential for this to work, there may be further study warranted. Unfortunately, the has not been much in terms of other solutions that have been proposed. The development and evaluation of guidance for this area was noted as a research need in the PCB LON study recommendations.

We did develop a MASH TL-3 upstream anchorage that you may wish to consider. http://mwrsf.unl.edu/researchhub/files/Report63/TRP-03-209-09.pdf

A similar comment would apply to the use of the transition as a downstream anchor on several of the layouts. However, as I noted, there may not be a better alternative at this time…

On the diagram for MEDIAN APPLICATION – ANCHORED–TRAFFIC SEPARATOR, the use of barriers pinned on both sides for deflection reduction has not been tested to NCHRP 350 or MASH. There have been concerns in the past that doing so may increase the potential for tipping of the barrier which leads to increased vehicle climb and instability. CALTRANS testes their K-rail segment in this configuration under NCHRP 350 and the results were not encouraging in terms of vehicle stability. This type of installation may potential work and there may not be a better alternative. However, further research is likely warranted. I believe we have noted this in previous Pooled Fund position papers and some states have shown interest. It was never funded.

You had also replied with the following:

However, I’m beginning to wonder if this should be discussed as a conference call amongst the pooled fund instead. I think a lot of states will have TBR-related questions and there isn’t a reason for you to answer it sixteen different times. I know Kansas has already asked and I doubt we’ll be the last ones. This would buy you a little more time and would (selfishly) help us know what the other DOT’s intentions are. Is everyone adopting the larger deflections? Is everyone moving to the tubed rail? Any interest in in-service evaluations of current deflections? I think this would be a great group discussion such that we all proceed as a complete group rather than sixteen different entities.

While I do see the value of getting all of the states on the same page, I am a little reluctant to turn this into a group wide discussion due to the fact that each state tends to have different concerns or preferences on these items. In addition, MwRSF does not typically wish to dictate hardware policies to states, and in many cases, states don’t want us to. That is generally better served by the RDG. As such, the discussion you are proposing would need to be more of a discussion of your proposed guidance and MwRSF could provide input and recommendations.

I will be putting this on the consulting web site to help distribute it unless that is an issue for you. If you really feel the desire to have that discussion with the group, I can try to set something up.

I don’t know how many states are implementing the reduced deflection system we did for WisDOT. Currently, the transition between that system and the free-standing PCB needs to be completed, so I don’t believe it has been widely adapted.

I do believe that several states are working towards implementing the larger barrier deflections as part of the MASH implementation efforts. I also believe this has caused some stress, and this has led to the development of an NCHRP problem statement to develop a MASH TL-3 PCB. We have proposed something similar in the Pooled Fund for several years, but it has not moved to the forefront.

In-service evaluation of work zone devices has been limited, but it would be interesting. I know that a study of work zone encroachments has been proposed several times but has not received funding.

Let me know what you think.

Thanks

_____________________________________

Good morning!

With the publishing of recent TBR-related report TRP-03-337-17, I’m trying to combine available MASH TBR guidance into one place and would appreciate a review by MwRSF to confirm this is the current guidance. I’ve attached schematics that incorporate my understanding discussed below and have included applicable pages numbers.

Full impact condition where TBR is adjacent to severe drop-off or missing bridge rail (pages 1, 2, 3, and 4)

Minimum of five segments of TBR on the approach, which may include flaring from tangent to 6:1 (62.5’)

Just a reminder that 6:1 flares were never crash tested or evaluated. This was a recommendation from NCHRP 358.

Additionally, flaring of the barriers outside of the LON may reduce their effectiveness in providing barrier tension in the LON, which would result in potentially larger barrier deflections. However, the research in TRP-03-337-17 required only 3 barrier segments in that region. As you have included an additional two barrier segments, this concern is much less.

Design-specific number of segments protecting the work area, where work/equipment storage/etc. may begin 80” from back of TBR

Minimum of seven segments of TBR on the trailing end, which may include flaring from tangent to 6:1 (87.5’)

For two-way protection, both the approach and trailing will be a minimum of seven segments (87.5’)

Notes:

Iowa has decided that a severe drop-off is any longitudinal opening greater than 36” that is at least 3” deep. The 36” value attempts to mimic cross-drain pipe guidance under Section 3.4.2.1 Traversable Designs of the 2011 Roadside Design Guide.

There is no hard data on vertical drop severity in terms of full-scale testing. Several studies have looked at cost benefit ratios of vertical drops based on ADT. I have attached two studies done at TTI. They may provide additional guidance on what level of vertical drop would be acceptable.

Additionally, I should note that the 36” lateral opening you note above was based on research and testing of culvert pipes at TTI. Those evaluations were based on a vehicle traversing 36” pipes. If a vehicle attempts to traverse a similar lateral gap at an angle, the actual distance it must traverse becomes greater. Thus, there may be a need to lower 36” gap size.

Iowa has decided that the deflection noted for Region A and Region C (132”) will be treated as “unlimited” deflection, thus extending the approach (originally three) and trailing (originally five) sections by two sections. The 132” value comes from TRP-03-337-17, top of page 148 and Figure 113 on page 154.
The 80” value comes from TRP-03-337-17, top of page 154 and Figure 113 on page 154.

The deflection for barrier segments AS1 and AS2 in your “ROADSIDE APPLICATION – UNANCHORED – OPPOSING TRAFFIC NOT WITHIN CLEAR ZONE” detail may be slightly higher than the 80” value listed due to their proximity to the upstream end of the PCB system. Because these barriers are within 7 barriers of the end of the system, the deflection may be closer to the 91” deflection shown for a 14 barrier system in Figure 110 and 113.

Iowa currently has the 80” value as 45” based on NCHRP 350 testing from TRP-03-113-03, top of page 14 and originally from TRP-03-64-96 bottom of page 45.
Five segments on approach end from TRP-03-337-17, Figure 113 on page 154 and Figure 114 on page 155.
Seven segments on trailing end from TRP-03-337-17, Figure 113 on page 154 and Figure 114 on page 155.
Five and seven segments were previously eight segments (100’) from TRP-03-209-09, middle of page 6.

85^th percentile impact condition for all other conditions (pages 1, 2, 3, and 4)

Minimum of five segments of TBR on the approach, which may include flaring from tangent to 6:1 (62.5’)

Design-specific number of segments protecting the work area, where work/equipment storage/etc. may begin 68” from back of TBR

Minimum of seven segments of TBR on the railing end, which may include flaring from tangent to 6:1 (87.5’)

For two-way protection, both the approach and trailing will be a minimum of seven segments (87.5’)

Notes:

Iowa has decided that the deflection noted for Region A and Region C (97”) of TRP-03-337-17 will be treated as “unlimited” deflection, thus extending the approach (originally three) and trailing (originally five) sections by two sections. The 97” value comes from TRP-03-337-17, bottom of page 150 and Figure 114 on page 155.
The 68” value comes from TRP-03-337-17, top of page 154 and Figure 114 on page 155
Iowa currently has the 68” value as 24” based on NCHRP 350 testing from TRP-03-113-03, top of page 14.
Five segments on approach end from TRP-03-337-17, Figure 113 on page 154 and Figure 114 on page 155.
Seven segments on trailing end from TRP-03-337-17, Figure 113 on page 154 and Figure 114 on page 155.
Five and seven segments were previously eight segments (100’) from TRP-03-209-09, middle of page 6.

Active testing to reduce deflection

Through additional testing and redesign, there appears to be a chance for the full impact and 85^th percentile deflections to be brought down from 80” and 68” to 41“ and 24” using steel tubes, but that design is still under refinement and an end transition has yet to be developed.

Notes:

The 41” value comes from TRP-03-295-14, bottom of page 247.
The 24” value comes from TRP-03-295-14, bottom of page 248.

Anchoring (pages 3, 4, 5, 6, and 8)

In cases where the combined lateral space requirement for barrier deflection and needed work area cannot be met, the barrier will need to be anchored. Anchoring the barrier will reduce the deflection down to 6” for both impact conditions.

Anchoring the barrier will not bring the barrier deflection down to 6”. The 6” number refers to the edge distance from the back of the barrier to the drop-off that was tested. From page 89, “The asphalt tie-down system for use with F-shape temporary concrete barriers was tested with a clear gap of 152 mm (6 in.) between the back side of the barriers and the edge of the vertical drop-off. Therefore, this distance is recommended as the minimum safe distance that the barrier system should be installed from the edge of the asphalt roadway. This 152-mm (6-in.) distance from the back side of the barrier does not reflect the distance for safe installation of the tie-down system adjacent to a rigid hazard. For this type of installation, designers must consider the working width of the system obtained during the full-scale testing.”

The 6” number also refers to the asphalt pin tie down. The concrete bolted tie-down uses an edge offset of 1”. This system was recently tested to MASH and was successful (Working width = 36.75”, dynamic deflection = 14.25”, static deflection = 8.25”). The asphalt pin testing to MASH is in que.

Notes:

The 6” value comes from TRP-03-180-06, middle of page 89.

Anchor Transitions (pages 3 and 4)

In cases where only parts of an installation need to be anchored, an anchor transition can be incorporated. This transition takes places over four segments with 1, 2, 3, and 3 anchors on the traffic side, both sides if used as a traffic separator, approaching fully anchored TBR, permanent barrier, or bridge rail. This anchor transition will also apply to certain crash cushions depending on their anchoring mechanism.

I should note here that the transitions we have developed were never evaluated with crash cushion systems. There may be potential for them to work with the crash cushions, but snag and load transfer to the crash cushion have not been evaluated. As you note, some designs may have better performance than others.

Notes:

Four anchor transition sections from TRP-03-208-10, Figure 4 on page 15.

Deflections between anchored sections (pages 3, 4, and 7 but specifically page 9)

One point of discussion that has risen from this is the expected deflection of unanchored TBR between two sections of anchored TBR. This might occur on bridge maintenance projects where the area of concern is only a couple feet longitudinally (replacing a joint for example), but there may be multiple areas of concern along the bridge. In an attempt to avoid anchoring the entire run of barrier, what deflections should be used within the unanchored portions?

The value of the deflection between anchored sections has never been defined, it would depend on the length and proximity of the unanchored PCBs to the anchored segments. In TRP-03-208-10, we impacted the upstream end of the transition from free-standing PCB’s to concrete median barrier at a location approximately 1 m upstream of the downstream end of the first unanchored barrier segment (barrier no. 5 in that test). The dynamic deflections in that MASH TL-3 test was 44.3 in. at the upstream end of barrier no. 5. Thus, this would be a conservative starting point. As an impact was moved farther from the anchored sections we would expect the deflections to increase to the free-standing PCB deflection of 80”. I think it would be reasonable to assume that that increase in deflection occurs over 3-4 barrier segments. This has not been formally analyzed, but it is likely the best answer I have without further analysis.

Your assistance in the matter is greatly appreciated. Since this is a lot to digest, if you feel discussion would be better served with a review followed by a conference call, we’d be more than welcoming.

Date September 11, 2017
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