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[Beltway]

What exactly are they doing, just restriping the existing roadways?  In the unbuilt I-83 interchange area, there is almost 2,000 feet of I-95 twin bridges with 3 lanes and 2 full shoulders on each, I just checked on Google Maps aerial view, and they don't look wide enough to restripe for 4 lanes and have even one full shoulder (presumably on the right).
http://www.mdta.maryland.gov/News/MDTA_News_Releases/i-95-improvement-project-to-add-capacity-north-of-the-tunnel

As best as I can tell, the work is mostly on the left (median) side.  Does not appear to be any (permanent) re-striping going on. Interestingly, the Google car was by there recently (October 2017) and here is a good image of what Concrete General is doing.

Looks like they are decking in between the two bridges, which looks like on aerial view could give 4 more feet of bridge deck each way, which should allow for a full 10 foot shoulder on the right as well as four 12 foot lanes and maybe a 4-foot shoulder on the left.

[Alps]

They had extended HTT tube closures soon after the Fort McHenry Tunnel opened in 1985, for major tunnel rehabs.  After all these years certainly it is time for another major rehab and modernization to tunnel systems. 

Wonder what they are going to do with ventilation, replace the plenum fans, or go the jet fan route like on the Norfolk-Portsmouth tunnel rehabs?

The $189 million is a lot of money, but it covers a lot more than just the 0.9 mile Canton Viaduct.

Here in NJ we have the Holland Tunnel, and I know that goes a lot more than 30 years between rehabs. In fact I think it's had exactly one. In no small part the issue is that you can't establish contraflow there, so you can only shut down one lane at a time or MAYBE get an overnight closure and force everyone up to the Lincoln Tunnel. Maybe. I would think you could go at least 50 years.

[Beltway]

They had extended HTT tube closures soon after the Fort McHenry Tunnel opened in 1985, for major tunnel rehabs.  After all these years certainly it is time for another major rehab and modernization to tunnel systems. 
Wonder what they are going to do with ventilation, replace the plenum fans, or go the jet fan route like on the Norfolk-Portsmouth tunnel rehabs?
The $189 million is a lot of money, but it covers a lot more than just the 0.9 mile Canton Viaduct.

Here in NJ we have the Holland Tunnel, and I know that goes a lot more than 30 years between rehabs. In fact I think it's had exactly one. In no small part the issue is that you can't establish contraflow there, so you can only shut down one lane at a time or MAYBE get an overnight closure and force everyone up to the Lincoln Tunnel. Maybe. I would think you could go at least 50 years.

What I don't know is the degree of rehab in each HTT project, I would need to see the details.  It may be that the first rehab was a light rehab.  On a quick look inside the tunnel I see what looks like strip florescent lighting fixtures, I don't think that is the original but that is old technology.

[mrsman]

They had extended HTT tube closures soon after the Fort McHenry Tunnel opened in 1985, for major tunnel rehabs.  After all these years certainly it is time for another major rehab and modernization to tunnel systems. 

Wonder what they are going to do with ventilation, replace the plenum fans, or go the jet fan route like on the Norfolk-Portsmouth tunnel rehabs?

The $189 million is a lot of money, but it covers a lot more than just the 0.9 mile Canton Viaduct.

Here in NJ we have the Holland Tunnel, and I know that goes a lot more than 30 years between rehabs. In fact I think it's had exactly one. In no small part the issue is that you can't establish contraflow there, so you can only shut down one lane at a time or MAYBE get an overnight closure and force everyone up to the Lincoln Tunnel. Maybe. I would think you could go at least 50 years.

Why can't contraflow be established in the Holland Tunnel?

[ixnay]

They had extended HTT tube closures soon after the Fort McHenry Tunnel opened in 1985, for major tunnel rehabs.  After all these years certainly it is time for another major rehab and modernization to tunnel systems. 

Wonder what they are going to do with ventilation, replace the plenum fans, or go the jet fan route like on the Norfolk-Portsmouth tunnel rehabs?

The $189 million is a lot of money, but it covers a lot more than just the 0.9 mile Canton Viaduct.

Here in NJ we have the Holland Tunnel, and I know that goes a lot more than 30 years between rehabs. In fact I think it's had exactly one. In no small part the issue is that you can't establish contraflow there, so you can only shut down one lane at a time or MAYBE get an overnight closure and force everyone up to the Lincoln Tunnel. Maybe. I would think you could go at least 50 years.

Why can't contraflow be established in the Holland Tunnel?

Is that even possible given that the Holland consists of two 2-lane tubes?

ixnay

[Alps]

They had extended HTT tube closures soon after the Fort McHenry Tunnel opened in 1985, for major tunnel rehabs.  After all these years certainly it is time for another major rehab and modernization to tunnel systems. 

Wonder what they are going to do with ventilation, replace the plenum fans, or go the jet fan route like on the Norfolk-Portsmouth tunnel rehabs?

The $189 million is a lot of money, but it covers a lot more than just the 0.9 mile Canton Viaduct.

Here in NJ we have the Holland Tunnel, and I know that goes a lot more than 30 years between rehabs. In fact I think it's had exactly one. In no small part the issue is that you can't establish contraflow there, so you can only shut down one lane at a time or MAYBE get an overnight closure and force everyone up to the Lincoln Tunnel. Maybe. I would think you could go at least 50 years.

Why can't contraflow be established in the Holland Tunnel?

I'll start by counterexample - the Lincoln Tunnel is set up that way. Thanks to the configuration of incoming roadways, you could literally go contraflow in any one of the Lincoln's three tubes, although the center tube is normally the only one that does that (and normally only one tube is out of service at any time). All the Port Authority needs to do is set up cone lines and signs.
Now, the Holland Tunnel. The toll plaza is beyond the last street on the NJ side, so there is no way to switch traffic over. If you put two-way traffic in the north tube, everyone would get to enter for free, and I can tell you right now that will never happen in a non-emergency. If you put them in the south tube, not as big a deal, but you would have to take a toll lane out of commission, and then use cones to get everyone back up to 12th Street. Now let's look at the NY side. For the north tube, you would have to have police in the road to direct traffic into the right side of Canal Street, and maybe Hudson (sharp right), because there's no traffic signal facing the (normally WB) tunnel approach. The south tube is again easier to deal with, but it would require everyone to enter the tunnel from Varick Street and stay in the right lane.
Can it be done? Anything can be done. But it won't.

[cpzilliacus]

What I don't know is the degree of rehab in each HTT project, I would need to see the details.  It may be that the first rehab was a light rehab.  On a quick look inside the tunnel I see what looks like strip florescent lighting fixtures, I don't think that is the original but that is old technology.

The post-1985 BHT project included a total replacement of the tunnel deck; a replacement of the tunnel lighting system; removal and replacement of the tiles on the walls; and  removal of the booths for the police officers (they were replaced by video monitoring)

What MDTA has planned now for the tubes is as follows (note - from memory, not from reading the IFB as amended):

• Removal of the wearing surface (only) of the concrete tunnel decks with some sort of hydraulic demolition process, and then installation of a new surface using latex-modified concrete (MDTA likes to do this for some reason - MDOT/SHA almost never does, having a revealed preference for "complete" deck replacement).  Note that a similar process was used on the westbound span of the WPL (Bay) Bridge in the early 2000's, and that did not end well, because the new surface did not adhere properly and started to crack and delaminate pretty quickly, and then a decision was made to do a total deck replacement with prefabricated sections so the bridge could be opened each morning to traffic (but on the flipside, the BHT, because of overhead clearance restrictions, does not carry as much truck traffic as the WPL).  It was thought that the delamination might have been due in part to the presence of salt on the remaining "bare" bridge deck and perhaps because of truck traffic.
• Replacement of the tiles where the tiling system has failed (and there's quite a lot of that, especially in the northbound tube for some reason).
• Replacement or repair of the pipes that supply water for firefighting use.
• Replacement of the lane control signals in both tubes.
• Replacement of the lighting systems in both tubes.

I know there were some other items as well, but I think the above were the  major ones.

[cpzilliacus]

Here in NJ we have the Holland Tunnel, and I know that goes a lot more than 30 years between rehabs. In fact I think it's had exactly one. In no small part the issue is that you can't establish contraflow there, so you can only shut down one lane at a time or MAYBE get an overnight closure and force everyone up to the Lincoln Tunnel. Maybe. I would think you could go at least 50 years.

The BHT tubes went from 1957 to about 1985 with very little maintenance having been done on them. 

Getting back to the Holland Tunnel, perhaps this might motivate the Port Authority to switch to all-electronic toll collection?

[Beltway]

What I don't know is the degree of rehab in each HTT project, I would need to see the details.  It may be that the first rehab was a light rehab.  On a quick look inside the tunnel I see what looks like strip florescent lighting fixtures, I don't think that is the original but that is old technology.

The post-1985 BHT project included a total replacement of the tunnel deck; a replacement of the tunnel lighting system; removal and replacement of the tiles on the walls; and  removal of the booths for the police officers (they were replaced by video monitoring)

What MDTA has planned now for the tubes is as follows (note - from memory, not from reading the IFB as amended):

• Removal of the wearing surface (only) of the concrete tunnel decks with some sort of hydraulic demolition process, and then installation of a new surface using latex-modified concrete (MDTA likes to do this for some reason - MDOT/SHA almost never does, having a revealed preference for "complete" deck replacement).  Note that a similar process was used on the westbound span of the WPL (Bay) Bridge in the early 2000's, and that did not end well, because the new surface did not ahere properly and started to crack and delaminate pretty quickly, and then a decision was made to do a total deck replacement with prefabricated sections so the bridge could be opened each morning to traffic (but on the flipside, the BHT, because of overhead clearance restrictions, does not carry as much truck traffic as the WPL).  It was thought that the delamination might have been due in part to the presence of salt on the remaining "bare" bridge deck and perhaps because of truck traffic.
• Replacement of the tiles where the tiling system has failed (and there's quite a lot of that, especially in the northbound tube for some reason).
• Replacement or repair of the pipes that supply water for firefighting use.
• Replacement of the lane control signals in both tubes.
• Replacement of the lighting systems in both tubes.

I know there were some other items as well, but I think the above were the  major ones.

Good summaries, thanks!  Thirty years is a long enough time that I am OK with the above rehab schemes, which could be categorized at major rehabs.  Do you know what is the plan with regard to ventilation systems?
....

The original Downtown Tunnel in Norfolk was opened in 1952.  When the second tube opened in 1987 the original tube was closed for almost a year for a major rehab, I don't have the exact details but it included new roadway, new lighting, and major upgrades to electrical, mechanical, drainage, fire, ventilation and surveillance systems

The 2013-14 rehab to both tubes --

Rehabilitation consists of structural, fire, life and safety improvements including:
§ Tunnel fireproofing for structural protection
§ A new jet fan ventilation system [plus removal of roadway tunnel ceiling which was also the floor of the plenum ventilation exhaust tunnel]
§ LED tunnel lighting which provides brighter lighting and uses less energy [LED is so much brighter that the new Midtown Tunnel tube doesn't need tiles, the walls are the fireproofing panels alone]
§ Tile and concrete repair
§ Exit and safety signage
https://www.driveert.com/wp-content/uploads/2013/08/ERT_factsheets_WestDowntownTunnel_Current.pdf

Well worth the money spent, IMO, bring the tunnels into 21st century standards.

The original Midtown Tunnel tube was opened in 1962 and got the same rehab treatment, and its first, completed in 2017.  I was down there a couple days ago and rode thru it for the first time since the rehab was completed and it looks very fine.

[Alps]

What I don't know is the degree of rehab in each HTT project, I would need to see the details.  It may be that the first rehab was a light rehab.  On a quick look inside the tunnel I see what looks like strip florescent lighting fixtures, I don't think that is the original but that is old technology.

The post-1985 BHT project included a total replacement of the tunnel deck; a replacement of the tunnel lighting system; removal and replacement of the tiles on the walls; and  removal of the booths for the police officers (they were replaced by video monitoring)

What MDTA has planned now for the tubes is as follows (note - from memory, not from reading the IFB as amended):

• Removal of the wearing surface (only) of the concrete tunnel decks with some sort of hydraulic demolition process, and then installation of a new surface using latex-modified concrete (MDTA likes to do this for some reason - MDOT/SHA almost never does, having a revealed preference for "complete" deck replacement).  Note that a similar process was used on the westbound span of the WPL (Bay) Bridge in the early 2000's, and that did not end well, because the new surface did not ahere properly and started to crack and delaminate pretty quickly, and then a decision was made to do a total deck replacement with prefabricated sections so the bridge could be opened each morning to traffic (but on the flipside, the BHT, because of overhead clearance restrictions, does not carry as much truck traffic as the WPL).  It was thought that the delamination might have been due in part to the presence of salt on the remaining "bare" bridge deck and perhaps because of truck traffic.
• Replacement of the tiles where the tiling system has failed (and there's quite a lot of that, especially in the northbound tube for some reason).
• Replacement or repair of the pipes that supply water for firefighting use.
• Replacement of the lane control signals in both tubes.
• Replacement of the lighting systems in both tubes.

I know there were some other items as well, but I think the above were the  major ones.

Good summaries, thanks!  Thirty years is a long enough time that I am OK with the above rehab schemes, which could be categorized at major rehabs.

I guess I would classify them as repair and resurfacing, not a major rehab. Major rehab in a tunnel should not happen every 30 years. Retiling, resurfacing, upgrade lighting, sure.

[Beltway]

Good summaries, thanks!  Thirty years is a long enough time that I am OK with the above rehab schemes, which could be categorized at major rehabs.

I guess I would classify them as repair and resurfacing, not a major rehab. Major rehab in a tunnel should not happen every 30 years. Retiling, resurfacing, upgrade lighting, sure.

What would you consider major rehab tasks ... complete replacement of roadway slab?  Complete replacement of ventilation fans?  Complete replacement of electrical conduits and wiring?  Complete replacement of fire mains and hydrants?

[jeffandnicole]

Good summaries, thanks!  Thirty years is a long enough time that I am OK with the above rehab schemes, which could be categorized at major rehabs.

I guess I would classify them as repair and resurfacing, not a major rehab. Major rehab in a tunnel should not happen every 30 years. Retiling, resurfacing, upgrade lighting, sure.

What would you consider major rehab tasks ... complete replacement of roadway slab?  Complete replacement of ventilation fans?  Complete replacement of electrical conduits and wiring?  Complete replacement of fire mains and hydrants?

Non-surface replacement, and/or structural replacement (meaning they have to go further deep into the roadbed or walls to get to what they need to work on).

Note: All of this could be done with just overnight/weekend shutdowns, but it would take the project a lot longer to complete. 

Whenever transportation agencies have these types of projects, they look to see if they should shut down the entire system completely, or shut down just one side leaving the other side open as is, or with 2 way traffic, or with 1 way traffic inbound in the morning/outbound in the afternoon. They could also build a temporary structure (not likely with a tunnel).  And they can just do construction outside of rush-hour periods, leaving the roadway fully open for rush hour.  There's benefits and disadvantages to every option, and no one option will please everyone. Depending on the situation, there's usually other options as well.

In this case, MD decided to go with 2-way traffic in one tunnel...at least for now.  Agencies know that some people will detour themselves to other routes, whether they be signed or unsigned detour routes.  Motorists tend to sort themselves out over time.

Of course, if there's a few high-profile or fatal accidents in the tunnel during rush hours, jamming up the area completely, MD could change their minds and go with another option.

[cpzilliacus]

Of course, if there's a few high-profile or fatal accidents in the tunnel during rush hours, jamming up the area completely, MD could change their minds and go with another option.

MDTA routinely  runs two-way traffic on two of its crossings - I-895 and the WPL (Bay) bridge. 

On I-895, almost only in  the overnights to service the lighting, and during the warm months, to wash the tunnel walls.  There have been more than a few crashes while running the BHT with all traffic in one tube.  For the extended two-way traffic operation, not clear to me if they are going to place a concrete barrier in the middle (and I have no idea if the tunnel deck is strong enough to support the added weight of a "portable" Jersey barrier), effectively creating a PennDOT-style cattle chute across the entire tunnel.

On the WPL (U.S. 50 and U.S. 301) they will run all traffic on one span in the overnights and sometimes on weekdays during the mid-day. 

[jeffandnicole]

Of course, if there's a few high-profile or fatal accidents in the tunnel during rush hours, jamming up the area completely, MD could change their minds and go with another option.

MDTA routinely  runs two-way traffic on two of its crossings - I-895 and the WPL (Bay) bridge. 

On I-895, almost only in  the overnights to service the lighting, and during the warm months, to wash the tunnel walls.  There have been more than a few crashes while running the BHT with all traffic in one tube.  For the extended two-way traffic operation, not clear to me if they are going to place a concrete barrier in the middle (and I have no idea if the tunnel deck is strong enough to support the added weight of a "portable" Jersey barrier), effectively creating a PennDOT-style cattle chute across the entire tunnel.

On the WPL (U.S. 50 and U.S. 301) they will run all traffic on one span in the overnights and sometimes on weekdays during the mid-day. 

In the evening/overnight hours, traffic tends to be a bit calmer...and when accidents occur they affect fewer people in the resulting backups.  A crash in contraflow mode during rush hours when people are already rushing and aggravated by traffic can lead to the entire region being affected by people trying to avoid the area and detour around it. 

A jersey barrier wall would certainly help, if there's enough room for it.

[MASTERNC]

PennDOT closed one tunnel completely when it rehabilitated the Fort Pitt Bridge & Tunnels in Pittsburgh.  They kept the detour for outbound traffic during both phases, because it ran better than in reverse.  When doing the inbound tunnel, they created crossovers on both sides, including on 376 in the "bathtub" area and all the exits on the other side of the bridge.  Not sure if it makes sense to detour one direction (maybe northbound since there are no exits between the I-95 south junction and the tunnel in that direction).

[Beltway]

PennDOT closed one tunnel completely when it rehabilitated the Fort Pitt Bridge & Tunnels in Pittsburgh.  They kept the detour for outbound traffic during both phases, because it ran better than in reverse.  When doing the inbound tunnel, they created crossovers on both sides, including on 376 in the "bathtub" area and all the exits on the other side of the bridge.  Not sure if it makes sense to detour one direction (maybe northbound since there are no exits between the I-95 south junction and the tunnel in that direction).

VDOT's rehabs of the Downtown and Midtown tunnels likewise closed one tunnel completely and they did not run two-way traffic in the other.  The recent rehabs involved weekend closures.

The issue with using a temporary concrete median barrier is that it is 24 inches wide, so that takes 2 feet away from the usable roadway.  Also there is no flexibility for handling a disabled vehicle, no way to get around it, and the only way a wrecker can get to it is by backing up for a very long distance.

[Alps]

PennDOT closed one tunnel completely when it rehabilitated the Fort Pitt Bridge & Tunnels in Pittsburgh.  They kept the detour for outbound traffic during both phases, because it ran better than in reverse.  When doing the inbound tunnel, they created crossovers on both sides, including on 376 in the "bathtub" area and all the exits on the other side of the bridge.  Not sure if it makes sense to detour one direction (maybe northbound since there are no exits between the I-95 south junction and the tunnel in that direction).

VDOT's rehabs of the Downtown and Midtown tunnels likewise closed one tunnel completely and they did not run two-way traffic in the other.  The recent rehabs involved weekend closures.

The issue with using a temporary concrete median barrier is that it is 24 inches wide, so that takes 2 feet away from the usable roadway.  Also there is no flexibility for handling a disabled vehicle, no way to get around it, and the only way a wrecker can get to it is by backing up for a very long distance.

That's why the Lincoln Tunnel uses pylons to separate traffic, even on the NJ 495 approach during bus lane operation. Since that was I-495 with pylons, I-895 can be done with pylons as well.
Re: major rehab (upthread) - yes, anything that is replacing entire systems or major components of the overall tunnel system, as opposed to spot upgrades or resurfacing.

[Beltway]

VDOT's rehabs of the Downtown and Midtown tunnels likewise closed one tunnel completely and they did not run two-way traffic in the other.  The recent rehabs involved weekend closures.
The issue with using a temporary concrete median barrier is that it is 24 inches wide, so that takes 2 feet away from the usable roadway.  Also there is no flexibility for handling a disabled vehicle, no way to get around it, and the only way a wrecker can get to it is by backing up for a very long distance.

That's why the Lincoln Tunnel uses pylons to separate traffic, even on the NJ 495 approach during bus lane operation. Since that was I-495 with pylons, I-895 can be done with pylons as well.

It was suggested that a hard barrier be used to separate traffic, that prompted my reply above.

Pylons (bollards) do provide visual separation but would not physically prevent a vehicle from entering the opposing lane.

Re: major rehab (upthread) - yes, anything that is replacing entire systems or major components of the overall tunnel system, as opposed to spot upgrades or resurfacing.

Such as replacing the plenum ventilation system with jet fans (axial flow fans)?  Which in the case of ERT also involved the removal of the ceiling of the roadway tunnel which was also the floor of the exhaust tunnel.

[Alps]

VDOT's rehabs of the Downtown and Midtown tunnels likewise closed one tunnel completely and they did not run two-way traffic in the other.  The recent rehabs involved weekend closures.
The issue with using a temporary concrete median barrier is that it is 24 inches wide, so that takes 2 feet away from the usable roadway.  Also there is no flexibility for handling a disabled vehicle, no way to get around it, and the only way a wrecker can get to it is by backing up for a very long distance.

That's why the Lincoln Tunnel uses pylons to separate traffic, even on the NJ 495 approach during bus lane operation. Since that was I-495 with pylons, I-895 can be done with pylons as well.

It was suggested that a hard barrier be used to separate traffic, that prompted my reply above.

Pylons (bollards) do provide visual separation but would not physically prevent a vehicle from entering the opposing lane.

Re: major rehab (upthread) - yes, anything that is replacing entire systems or major components of the overall tunnel system, as opposed to spot upgrades or resurfacing.

Such as replacing the plenum ventilation system with jet fans (axial flow fans)?  Which in the case of ERT also involved the removal of the ceiling of the roadway tunnel which was also the floor of the exhaust tunnel.

Well again, my distinction was work that shouldn't need to be performed every 30 years. A system upgrade may be disruptive, but as long as it lasts more than 30 years I'm okay with doing it. (It may have been overlooked the last time.)

[jeffandnicole]

Pylons (bollards) do provide visual separation but would not physically prevent a vehicle from entering the opposing lane.

Using the I-495 example, it's extremely rare to hear of another vehicle crossing thru the pylons, even though when traffic is moving, it's well above the speed limit with about a 100% tailgating rate. The visual effect seems to be substantial in keeping traffic in their proper lane.  The most common accident is usually a bus bumping into another bus in the XBL.  Considering how close they run behind each other, it's probably amazing it doesn't happen more often.

[Beltway]

Re: major rehab (upthread) - yes, anything that is replacing entire systems or major components of the overall tunnel system, as opposed to spot upgrades or resurfacing.

Such as replacing the plenum ventilation system with jet fans (axial flow fans)?  Which in the case of ERT also involved the removal of the ceiling of the roadway tunnel which was also the floor of the exhaust tunnel.

Well again, my distinction was work that shouldn't need to be performed every 30 years. A system upgrade may be disruptive, but as long as it lasts more than 30 years I'm okay with doing it. (It may have been overlooked the last time.)

They didn't have jet fans back then, not sure when the first was installed, but part of what made them feasible was vast reductions in motor vehicle pollutants enabled by advancing technology.

[Beltway]

Pylons (bollards) do provide visual separation but would not physically prevent a vehicle from entering the opposing lane.

Using the I-495 example, it's extremely rare to hear of another vehicle crossing thru the pylons, even though when traffic is moving, it's well above the speed limit with about a 100% tailgating rate. The visual effect seems to be substantial in keeping traffic in their proper lane.  The most common accident is usually a bus bumping into another bus in the XBL.  Considering how close they run behind each other, it's probably amazing it doesn't happen more often.

That is true and if there is an emergency they can be driven through without damaging the vehicles.

[froggie]

VDOT's rehabs of the Downtown and Midtown tunnels likewise closed one tunnel completely and they did not run two-way traffic in the other.

As I understand it, the Midtown Tunnel rehab was done by closing 1 lane and not closing the tunnel completely.

[Beltway]

VDOT's rehabs of the Downtown and Midtown tunnels likewise closed one tunnel completely and they did not run two-way traffic in the other.

As I understand it, the Midtown Tunnel rehab was done by closing 1 lane and not closing the tunnel completely.

Removing the tunnel ceiling in segments and installing jet fans?  That is a major job and even with the tube closed to traffic there is limited room to work.   And then it would have been only on weekends.

[cpzilliacus]

They didn't have jet fans back then, not sure when the first was installed, but part of what made them feasible was vast reductions in motor vehicle pollutants enabled by advancing technology.

I think the first "jet" fan I  saw in the  U.S. was on the PTC's "new" Lehigh Tunnel (the tube that normally carries southbound traffic (though I think PTC can run two-way traffic in most or all of its tunnels if needed, as the crossover ramps are there).

Getting back to the BHT, I do not think MDTA is going away from its "traditional" approach to tunnel ventilation using plenums and fan buildings.

Anyone looked at the plans for the CBBTD's new Thimble Shoal Tunnel?