Quote:
Originally Posted by hereinaustin
Better yet, just tunnel under the river and keep the space above open.
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Congress and Riverside per elevation charts is around 425 feet above sea level. The Colorado River is around 400 feet above sea level. The base of a rail tunnel under the Colorado River would have to be at least 25 feet lower than the river, accounting for track bed, tracks, and catenary wires above the trains. That's assuming a square shaper tunnel, an arch shaper tunnel might need to be deeper. So the tunnel will have to have at least a 50 feet vertical drop (or rise) from a southern portal near Riverside. The northern portal is in this case unimportant because the trains will be running supposedly in a subway north of the river. Google Earth tools suggests Riverside is 950 feet away from the rivers southern bank opposite Trinity north of the river (just about everyone's choice for the rail line route.
Some math follows
Best case scenario using every foot for the grade placing the portal at Riverside's northern curb
50/950 x 100 = 5.25% grade.
That is very steep, even for light rail trains. But doable because almost all light rail trains are allowed 6% grades. It is not the propulsion machinery capability to climb uphill that limits the grades, it is the braking capability of the brakes on the downhill that is more limiting. There are just so many brakes you can put on an axle.
If they were to build a bridge over the river at the same location, then where the northern portal is place would be more important. But CapMetro would have the advantage of reducing the vertical elevation change to 25 feet or so, since they wouldn't have to go lower than the river anymore. It should be easy for them to do that. So not only should the bridge over the river be cheaper to build, it should be easier to operate trains on as well.
A great example where construction photos are still present of light rail going underground to a station at Google Earth is the Rideau Station just east of the Rideau Canal in Ottawa to the southeast portal to its' south. 2000 feet to drop around 87 feet.
Per
https://en.wikipedia.org/wiki/Rideau_station
It is 26.5 meters deep or 87 feet deep.
2000 feet in a direct line between portal and eastern edge of station construction visible using Google Earth tools.
Math = 87/2000 x 100 = 3.95% grade. Far less than the 6% grade discussed earlier.