How are train crews warned a drawbridge is open? Do they rely on a special block signal or being told by a dispatcher at the bridge; or is it now GPS? If a signal is used, how far away should it be from the bridge so to prevent the train from plunging into the water since there are no gates and other warning devices used by automobiles?
There is normally a signal, block or otherwise at a drawbridge to indicate whether its open or closed.
The signal at the bridge may be 20-200 feet from the bridge. There is probably an approach signal 1-2 miles before that. If there are no signals or approach signs then there is a sign 1-2 miles away and all trains have to approach the bridge prepared to stop.
The dispatcher may be the bridge operator.
Virtually nothing on railroads is “controlled” by GPS. Certainly not a drawbridge. GPS measures where something is. A drawbridge, whether open or closed is always in the same place.
You’d probably have an interlocking signal rather than a block signal. Some single-head block signals are “absolute” (red means stop) and some are “permissive” (red means slow way down, prepared to stop if necessary). By adding a “dummy” second head that is always red, it prevents any tragic misunderstanding of confusing an absolute signal for a permissive one by showing red-over-red which always means stop. I agree there would be an approach signal, it’s distance would in part be determined by the speeds of the trains involved among other things. The south end of the old CGW lift bridge in downtown St.Paul has an approach signal (which appears to always be yellow) maybe a few hundred yards from the bridge over the Mississippi, but speeds on that track is usually pretty slow.
BTW I interviewed to be a bridge operator a few years ago, one interesting thing I learned was that river traffic has the ‘right of way’ since a train can stop on it’s tracks pretty easily…a barge and tugboat can’t stop on a flowing river very well. [swg]
“Stix” is right. Signals protecting drawbridges are interlocking signals with absolute stop indications, meaning “stop and stay” rather than “stop and proceed” like the typical block signal. To the railroad, a drawbridge is pretty much the same as crossing another railroad at grade.
So long,
Andy
The drawbridge over the Sandusky Bay has a operator and he controls the approach signals to the bridge…Oddly this is a low bridge that needs raised for private vessels as small as 21’ cuddy cabins.
I got a ‘cabin tour’ of the ex-New Haven Scherzer rolling lift bridge just south (railroad west) of the old Pelham Manor station, and got to see the interlocking in action. It was an old-style ‘armstrong’ frame, with levers for the signals, for the bridge itself and locking levers (to assure that nothing was moved out of sequence.)
First the approach signals were unlocked, set to ‘approach prepared to stop’ and locked. Then the positive stop signals, located at the shoreline just short of the approach spans (a hundred yards or so from the lifting section,) were unlocked, set to ‘stop’ and locked Finally, the bridge locking lever could be unlocked, and the bridge rolled up and back. The whole procedure took several minutes, and almost as long again when the bridge was lowered.
The parallel road bridge, a double-rollback span, operated more quickly, but had normally-green traffic lights that had to cycle through yellow to red, with an additional delay as the railroad-style gates came down, before the bridge could be opened. That gave pedestrians time to clear the moveable spans.
Chuck (Modeling Central Japan in September, 1964)
On lightly used lines, often the approach signal was left permanently at yellow (approach prepared to stop). This also might occur at diamonds. A semaphore with the blade anchored at yellow might provide the indication, since it has the advantage that no power is needed to illuminate a bulb.
The one hazard is that the train crew becomes accustomed to the signal always showing the “approach” indication, and assumes that everything will be set up for them at the drawbridge. I wonder if that was the case in the event a month or two back in the east which left the lead locomotive hanging over the end at an open span.
John
Don’t forget the smashboard:
http://www.railpictures.net/images/d1/3/5/8/5358.1211652059.jpg
These systems weren’t perfect as evidenced by the engine crew missing a red signal resulting in three Southern Pacific Baldwin roadswitchers attempting to pass over an open drawbridge on the Napa River. All three units were scrapped after being pulled from the river. (See page 87 of Strapac’s Southern Pacific Historical Diesels Volume 11.)
Mark
Back in the late 1970s Conrail’s former PRSL swing bridge in Paulsboro NJ was manually operated. The home signals were mechanically interlocked smashboards and the distant signals were simply yard limit signs in advance of the smashboards. The bridge is over Mantua Creek ( Mantua - There’s a name that ought to ring a bell with model railroaders)
Here in Nova Scotia the Canso causeway between the mainland and Cape Breton has a swing bridge as part of it (to allow for boat passage) which is crossed by both the highway and the Cape Breton and Central Nova Scotia Railway line. This bridge originally had interlocking signals protecting it, but as traffic is slow on the line these days, they have now been blacked out. To replace them, a red sign (the octagonal all red, letterless stop-type sign) has been attached to the signal, as a permanent indication that all trains must stop and then proceed across the bridge with caution. Speeds are very slow on this part of the line anyway, and the bridge is (in most weather) clearly visible from the signal point.
Smashboard signals were common at interlocked drawbridges. They were rare at other kinds of interlockings but not unheard of. The blade would extend over the track so that if a train overran the signal, the blade would be broken (hence the reaon for the word “smashboard”). Hopefully that would be noticed by the engine crew if not too late to stop before fouling the bridsge. Also, the broken blade would leave evidence that the signal had been overrun if the train had overun the signal but in time to avoid the open drawbridge. (Sometimes, especially in the old days, railroaders would have a code amongst themselves and not tell managment if there was a screw up and no evidence of the error. There were no hours of servic e laws way back when and fatigue was an even bigger factor back then as was alchohol on the job.)
Some of the worst train wreck disasters in history were as a result of a train running into an open drawbridge with passnegers. A commuter train, for example, in the drink could result in great loss of life.Not all drawbridges were large or made from steel. I have one incident recorded in a history project I am working on that occured in 1873 on a timber drawbridge over a feeder canal to the Wabash & Erie canal at Fort Wayne, Indiana. A Fort Wayne, Jackson & Saginaw American type (4-4-0) and two cars ended up in the feeder canal at night when they rounded the curve and found out the hard way that the bridge was open. Reportedly the bridge watchman was mysteriously not on duty that night!