4 ms·

Part of the expected cost reduction is in reduced cross sectional area, so a train won't fit into the 12 ft tunnels they're planning to make.

by tbabb 9y ago

astrodust 9y ago
You might not be able to fit a full-sized train in there, but don't forget the original New York City Subway had to fit in some relatively tiny tunnels: http://www.nycsubway.org/wiki/The_Construction_of_the_Harlem_River_Tubes_(1915) http://www.nycsubway.org/wiki/The_Construction_of_the_Harlem... Subway trains are often engineered to specification, so if you have a tunnel of a particular size the manufacturer can make a train for it. The precursor to the modern subway was a strange pneumatic system that would fit in that tunnel as well: http://www.nycsubway.org/wiki/Beach_Pneumatic_Transit http://www.nycsubway.org/wiki/Beach_Pneumatic_Transit
spditner 9y ago
There are a few reasons that I'm aware of that new projects typically bore larger tunnels versus a 12ft bore that would reduce construction and operational costs: - Logistically, it is difficult to get a cement truck into a small tunnel, as each truck would need to back out of the tunnel. You end up offloading into smaller cement trucks that can turn around, which is the headache that the Eglinton LRT tunnels is dealing with now - Need space for a level floor, conduits/tunnel infrastructure and evacuation walkways - Air flow. The rail car is an effective cork. Small tunnels require more ventilation and draw more power to push that air being compressed around -- unless the underlying truck is going to be propelling itself via the air Barcelona's system is apparently the new gold standard for how it should be done [1] They were able to build it out at ~$39 million/km[2] [1] http://www.skyscrapercity.com/showthread.php?t=1866842 http://www.skyscrapercity.com/showthread.php?t=1866842 [2] https://pedestrianobservations.wordpress.com/2013/06/03/comparative-subway-construction-costs-revised/ https://pedestrianobservations.wordpress.com/2013/06/03/comp...
- tomarr 9y ago
  You're missing the biggest one - evacuation. The reason many tunnels are oversized is to allow walkways for people to evacuate using in an emergency. This drives the size up a fair bit.
  - ebalit 9y ago
    "- Need space for a level floor, conduits/tunnel infrastructure and evacuation walkways" Seems like you missed this part.
ianburrell 9y ago
The London Underground deep-tube lines run in 11.5 to 12 ft diameter tunnels. The Glasgow subway uses 11 ft diameter tunnels.

Part of the expected cost reduction is in reduced cross sectional area, so a train won't fit into the 12 ft tunnels they're planning to make.

by tbabb 9y ago

Part of the expected cost reduction is in reduced cross sectional area, so a train won't fit into the 12 ft tunnels they're planning to make.

astrodust 9y ago

You might not be able to fit a full-sized train in there, but don't forget the original New York City Subway had to fit in some relatively tiny tunnels: http://www.nycsubway.org/wiki/The_Construction_of_the_Harlem_River_Tubes_(1915) http://www.nycsubway.org/wiki/The_Construction_of_the_Harlem... Subway trains are often engineered to specification, so if you have a tunnel of a particular size the manufacturer can make a train for it. The precursor to the modern subway was a strange pneumatic system that would fit in that tunnel as well: http://www.nycsubway.org/wiki/Beach_Pneumatic_Transit http://www.nycsubway.org/wiki/Beach_Pneumatic_Transit

spditner 9y ago

There are a few reasons that I'm aware of that new projects typically bore larger tunnels versus a 12ft bore that would reduce construction and operational costs: - Logistically, it is difficult to get a cement truck into a small tunnel, as each truck would need to back out of the tunnel. You end up offloading into smaller cement trucks that can turn around, which is the headache that the Eglinton LRT tunnels is dealing with now - Need space for a level floor, conduits/tunnel infrastructure and evacuation walkways - Air flow. The rail car is an effective cork. Small tunnels require more ventilation and draw more power to push that air being compressed around -- unless the underlying truck is going to be propelling itself via the air Barcelona's system is apparently the new gold standard for how it should be done [1] They were able to build it out at ~$39 million/km[2] [1] http://www.skyscrapercity.com/showthread.php?t=1866842 http://www.skyscrapercity.com/showthread.php?t=1866842 [2] https://pedestrianobservations.wordpress.com/2013/06/03/comparative-subway-construction-costs-revised/ https://pedestrianobservations.wordpress.com/2013/06/03/comp...

tomarr 9y ago
You're missing the biggest one - evacuation. The reason many tunnels are oversized is to allow walkways for people to evacuate using in an emergency. This drives the size up a fair bit.
- ebalit 9y ago
  "- Need space for a level floor, conduits/tunnel infrastructure and evacuation walkways" Seems like you missed this part.

ianburrell 9y ago

The London Underground deep-tube lines run in 11.5 to 12 ft diameter tunnels. The Glasgow subway uses 11 ft diameter tunnels.