A Blast From The Past, In The Past

My mental image of hand-drawn, colored engineering renderings is that they were a nineteenth-century phenomenon. These drawings prove me wrong: they’re a 1922 description of the lower-Manhattan tunnel under the Hudson River, then in the early stages of construction. The second page is signed by Clifford Holland, the chief engineer of the project, although that doesn’t mean that he drew it. Holland died of a possibly-stress-related heart attack in 1924, at the age of 41; the tunnel was named for him almost immediately afterwards.

The second page particularly looks very old-fashioned, with the hand-colored uniform on the tunnel guard, and on the cars. Despite the art – or maybe because of it – there’s a lot of information in the pictures in addition to the facts presented in the text at the bottom. Things not explicitly stated in the text:

• The line chosen minimized condemnation of buildings by passing through the train yards in Jersey City and streets in Manhattan.
• The use of piers over the ends of the river portion of the tunnel allowed the mid-river ventilations shafts to not be isolated structures in the river, exposed to ship traffic.
• Like the Pennsylvania Railroad tunnels some 15 years earlier, the tunnels had to “float” in the mud because of the depth to bedrock.
• The slow speeds of traffic back then meant that a Jersey City exit with two right-angle turns was considered possible.
• The geometric clearances in the tunnel were just fine for the size vehicles in use at that time.
• The assumption was that there would be an active tunnel-personnel presence along the path.

One item in the text caught my eye, although all of the text is worth reading if you’re interested in the tunnel. “Air will be discharged and removed continuously throughout the length of the tunnel – no longitudinal movement of air.” The cross-section clearly shows the airflow from the supply plenum below the roadway to the exhaust plenum – helpfully colored smokey gray – above the roadway. It’s the second half of the sentence that’s interesting. Long underwater rail tunnels had no ventilation. The obvious example – the Pennsylvania tunnels to the north – relied on (a) the absence of smoke because the trains were electric-powered and (b) piston action, where the air in the tunnel was changed by being forced through the tunnel ahead of each train. Vehicular tunnels had a problem in that they were being more actively polluted by engine exhaust and piston action wouldn’t work; this sentence is addressing that concern head on.