Could a subway train system be built without tearing up the entire road above (just digging underground)?

Question

Hypothetically, could this be done? Or would the road above need to be demolished?

Answer 1

In London there are two kinds of 'subway' trains. There are those, like the NY subways, which use cars the same size as main line trains. These lines were built on the 'cut and cover' method, already described in a previous answer which did require the road above to be torn up. The other type are the small 'tube' lines which were built without (much) disruption to the ground above by tunnelling using 'shields'. As a matter of interest all underground railways in London tend to follow the line of the street as this did not require the builders to pay out wayleave fees  which would have been the case if they had gone under private land (as ownership of land in English law - notionally - goes to the centre of the earth)

Answer 2

What you describe is the "tube" method of tunnel construction.

You dig a large hole near the start of the line and lower down all the parts and build the tunnel boring machine underground. You then bore the tunnel, casing it as you go. When you get to the end of the line, you bore an additional length of tunnel and bury the the boring machine, etc. in it (cheaper than dismantaling it and taking back to the surface.

The only above-ground disruptions are the construction of the stations.

The technology is about 150 years old.

Answer 3

currently thats how the Gold Line East side exestition is getting

built  in Los Angeles

(the contractor even gave names to the two tunnel drilling machines)

Answer 4

There are tunnelling machines doing exactly what you are suggesting beneath cities all the time.

Answer 5

In NYC, part of a new subway is being built just as you say.  All digging is done underground.  NYC don't often add new route because of the disruption to road traffic.  And that is exactly the reason for this method.

Good Luck.

Answer 6

Yes, it is called tunneling.  The ripping up of the road is called "cut and cover".  Two different concepts. You can read more about this if you look up the history of the construction of the New York City subway system.

Answer 7

Yes, it's been done with TBMs (tunnel boring machines). But TBMs are very expensive, and can only be used once. When they're finished, they tunnel out of the way and are left buried. Too big to come up again.