how is the underwater tunnel ventilated?
It contains a system of vents that run transverse, or perpendicular, to the tubes
Holland Tunnel
The Holland Tunnel was the first mechanically ventilated underwater vehicular tunnel in the world. It contains a system of vents that run transverse, or perpendicular, to the tubes. Each side of the Hudson River has two ventilation shaft buildings: one on land, and one in the river approximately from the respective shoreline. 
what does the holland tunnel look like underwater UNANSWERABLE what is this tunnel? It is a vehicular tunnel under the Hudson River is this tunnel built to connect cities? Yes, Lower Manhattan with Jersey City does the river flow through these aforementioned cities? Yes are there any other tunnels build under this river? Yes, Lincoln Tunnel who are the operating authority for the tunnel mentioned at the beginning? Port Authority of New York and New Jersey (PANYNJ) when was the aforementioned authority established? 1921 does the tunnel (mentioned at the beginning) consists of tubes? Yes, a pair of tubes who is the chief engineer on the project? Clifford Milburn Holland
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Holland Tunnel [SEP] Ventilation
The Holland Tunnel was the first mechanically ventilated underwater vehicular tunnel in the world. It contains a system of vents that run transverse, or perpendicular, to the tubes. Each side of the Hudson River has two ventilation shaft buildings: one on land, and one in the river approximately from the respective shoreline. All of the ventilation buildings have buff brick facades with steel and reinforced-concrete frames. The shafts within the river rise above mean high water; their supporting piers descend , of which are underwater and are embedded in the riverbed. The river shafts double as emergency exits by way of shipping piers that connected each ventilation shaft to the shoreline.