Quote:
Originally Posted by ardecila
It's not like it'll be a tunnel. There's a pinch point of the railyard at Central, so an "underpass" would be more like a trench with a few rail bridges over it. The cost will reflect whether that trench needs retaining walls or can use sloped sides.
Viva, your comparison to the Orange Line seems appropriate. Likely, much of the cost comes from complex construction staging needed to preserve an active railyard.
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Indeed there is a pinch point and it lines up with Central Avenue - but it turns out even the widest point of the yard isn't all that wide anyway (maybe a quarter mile rather than a whole mile). And the pinch point isn't absolute, because there are still several tracks, and roadways, going east-west far north of and south of the pinch point, as well as curved north-south rails leading into the pinch point. So a quick underpass would not work. But you're nevertheless most likely right that a trench would be chosen over a tunnel, assuming the RR wasn't feeling too protective about retaining every square foot of its yard. (And if it isn't too protective, then they might not object to occasional column footings either, so that an overpass ends up as the mutually preferred solution.)
But looking at the aerial photos drives one new point home: Between 65th and 79th (excluding the yard), it looks like there is a fair amount of land to be acquired in order to convert it to a 6-lane or 8-lane right of way from a sleepy industrial park-like access road -- the stretch continually has buildings, driveways and/or parking lots of businesses, schools/parks, and residences abutting right up to it. It also intersects another RR line at 75th. All of the intersections would need to be completely redone as main artery intersections, including signaling, turn lanes, maybe modifications to the crossing streets, etc. So that's probably where much of the half-$billion cost comes from.
Initially it's confusing because "Central Avenue Bypass" kind of suggests it's just an "overpass" or "underpass" over an obstacle, namely the everpresent railyard -- but once you notice "bypass" refers to an entire new route through a part of the city, the price maybe starts to make sense.