06-29-2021, 03:27 PM
(06-29-2021, 10:22 AM)tomh009 Wrote: Is there a reason why we need 100m+ ramps at both ends? Could we not put in stairs and an elevator (and/or escalator)? It would take far less space, and the elevator likely costs much less than 100m of concrete ramp.
You say “and/or”; but if there isn’t a ramp, an elevator would be needed. An escalator is very convenient for many but just doesn’t do the job for everybody, in particular for people in wheelchairs.
As to length, maximum slope for a ramp is typically 1/12. So to get over the expressway, you need about 5m clearance under the bridge, plus a bit for the floor thickness; let’s just say 5m. That requires a 60m ramp to get down to the level of the expressway. But it sits on an embankment; I don’t know how high but 2m by the time you get way off the expressway right-of-way wouldn’t surprise me; might be more since I don’t really know the topography. So that’s another 24m for a total of 84m. But actually I don’t think 1/12 takes into account the flat spaces you need every so often in a long ramp, so longer than that.
This is where the tunnel idea might help: let’s assume a spacious 3m height tunnel, and assume a 1m thickness between the ceiling and the roadway surface. I’m guessing 1m is thinner than you would want for the easiest style of construction (tunnel far enough down that the actual roadway can be built exactly the same as where there is no tunnel), but this gives us a tunnel floor 4m below the roadway. But if we assume the surrounding land is already 2m below the roadway, we might only have to ramp down 2m more, which would take about 24m (plus more for flat spaces).
But of course to figure out feasibility for real, not just my quick estimate, one would have to check the real topography and the real, detailed, design standards for ramps.