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2 hours ago, Triton said:

It's for drainage.

The one theory I have for why they split the tunnels into two is that federal regulation probably has some rules when it comes to tunnel length and the requirement to build a ventilation system to take out vehicle exhaust. The price tag probably would have risen substantially if they made one long tunnel with those requirements as opposed to two smaller tunnels. On top of that, you probably also would have been required to build emergency exits every-so-often. Again, that's just a theory I have.

I think you are correct on the ventilation aspect.  I recall reading about such ventilation requirements regarding the below-grade segments in NHHIP. If a "tunnel" is more than x' feet long mechanical ventilation is required.

Found this:  

NFPA [National Fire Protection Association] 502 does not mandate that mechanical ventilation be provided in tunnels less than 1000 m (3280 ft.) long, but does require an engineering analysis be performed. Historically, for short tunnels, common practice is that they are not mechanically ventilated. However, societal awareness about the serious nature of fires in road tunnels, coupled with the development of NFPA 502, has led to a need to demonstrate quantitatively whether mechanical ventilation is needed. NFPA 502 states that emergency ventilation shall not be required in tunnels less than 3280 feet in length, where it can be shown by an engineering analysis that the level of safety provided by a mechanical ventilation system is equaled or exceeded by enhancing the means of egress or the use of natural ventilation

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20 minutes ago, thatguysly said:

Are they building a bridge over the water feature between the tunnels or will it be a culvert system? The rendering make me think culvert but that doesn't seem as hospitable to the ecosystem.

We only support land animals, not water ones.

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18 minutes ago, samagon said:

what about amphibians that don't want to go all the way around the land bridge?

They can shop at the GFR and take their chances after...

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