And affordable. Both are questionable when something like 135 ft. of vertical clearance at high tide are needed under the fixed bridge for ocean-going ships, and the maximum grade is limited to around 2% = 105 ft. per mile (somewhat less with curve compensation deducted). The grade limitation means that in flat coastal terrain, each approach is going to be around 1.5 - 2 miles (with vertical curves), for a total span length of 3 - 4 miles, a majority of which will be over 50 ft. above ground. (Obviously, high bluffs instead on the approaches make this all much simpler.) I can think of only a handful like that: Hell Gate Bridge in New York City, and the Huey P. Long Bridge in New Orleans - are there any others ? Even the ex-SP Carquinez Strait Bridge in California has a lift bridge section (see: http://bridgehunter.com/ca/contra-costa/bh38645/ ).
- Paul North.
And we’ve seen, all too often, that fixed-span bridges aren’t exempt from errant vessel strikes.
UP wants to replace its bridge over the Mississippi with a fixed span. I don’t think it’ll have to go into the hundred-foot-plus range for clearance, but the approaches will be pretty interesting, I suspect.
Brother North, better delete the Hell Gate Bridge from your list of bridges between high bluffs. On the Queens end it’s approached by a long, high viaduct. The Randall’s Island end is on a viaduct that doesn’t reach local ground level until it’s several hundred yards into the Bronx - and there’s a fixed truss bridge over Bronx Kill, the channel connecting the Harlem River to Long Island Sound. I seem to recall the total length of spans as something like 18,000 feet, including ALL of the part over Randall’s Island and Ward’s Island. I haven’t been there in years, but I seem to remember that the highest point on Randall’s Island is only about 25 feet above mean high water. The viaduct is a good bit taller than that.
The Wikipedia entry includes some very good photos taken during construction and since.
Chuck (former Noo Yawker)
An excellent side-by-side comparison of a movable bridge with a high-clearance fixed bridge is in Chicago on the Calumet River. The PRR/NYC vertical lift bridges are next to the Chicago Skyway Toll Bridge. 135-foot vertical clearances are required for lake boats and a handful of ocean freighters.
HUMPH
NYCT operates over two major fixed bridges (Manhattan and Williamsburg) and that is from subway tunnel to bridge and back to subway tunnel. OK, they are not as tall as the GWB or the VNB but they are fixed bridges nonetheless. Yes, all subway cars are powered and can climb grades closed to freight lines but it can be done.
ROAR
And, when you see the length of the approaches to the Skyway bridge, think of how much longer it would take a railroad to climb that high. I suspect that the approaches would run from roughly Englewood to Whiting.
Chuck/ TOMIKAWATT - my parenthetical was apparently more confusing than helpful, because I didn’t intend to infer that the Hell Gate Bridge was between bluffs. Nevertheless, all the details you provide corroborate very well with the main points that I did intend for my post, as do the subsequent posts above from the Chicago contingent (the other Paul, and Carl) - thanks to all ! [bow]
- Paul.
Although not as high as a ocean going ship bridge, the UP (MoPac, et al.) bridge across the Mississippi at Thebes, IL is high enough to clear river traffic. It takes advantage of high bluffs, where Crowley’s Ridge is cut by the river, to avoid long approach spans. There are also some high bridges across the Ohio.