What is the standard for trains going over a bridge? Are they ussually lower than the track speed for the no bridge section of track (e.g. Maximum track speed is 50 MPH, would the speed over a bridge usually at a reduced speed)?
The only reason a bridge would have a lower speed than the track around it would normally be because of a structural deficiency or a clearance problem. Those structurally deficient bridges may just be older bridges (E-55 or E-65 rating) , not designed to the current E-80 rating and seeing 100-135 ton axle loadings on a regular basis.
Wonder if your question somehow is tied to a heavy axle load (HAL) issue where slowing down trains extends the life of a bridge by reducing impact cycles?
There is no standard speed or rule for going over bridges. Each bridge, type of bridge, material bridge is made of, when it was built, why it was built, amount of traffic, type of traffic, train speed, train wieght, type of train, number of trains, grade up,grade down, type of track, conditon of track, condition of bridged relative to relatives, railroad owner, railroad operator, weight of locomotive, weight per axel; if there is there anything I missed or didn’t mention add that in, too. I am sure Acela’s are zipping across bridges at top speed while the local on a weed grown back track is walking.
A lot of questons here can be answerd the same way: there are so many variables, idiosyncracies, philosophies, contsturction charateristics, equipment differences, that each individual piece of equipment, stretch of track, and types of bridges, is uniique unto itself. Just have to read the books of rules, employee timetables, other instruction books and bulletins as issued by each railroad for each circumstance to be sure.
We have a couple of 10 MPH bridges. I’m sure both could handle the track speed on either side of them. The reason we slow down is so the passengers can enjoy the view… We are a “scenic railroad,” after all.
Unless the maintenance has been deferred on a bridge that would dictate a reduced speed the answer would be track speed as dictated by the timetable for that particular line segment.
Tim
NS Locomotive Engineer
Not usually, but sometimes yes. Typical examples would be an old spindly open-deck steel girder or truss bridge or a timber trestle in marginal condition; rarely is this seen with masonry, concrete, or ballast-deck bridges, regardless of age and even if their condition seems superficially poor. A bridge on a curve is also more likely than most to have a speed restriction, especially if it’s a high one. Finally, a bridge near the end of its service life on an economically marginal line may have speed restrictions applied rather than repairs and replacements. A current example is the old and deteriorated ex-Erie/ E-L/ CR/ now NS Portageville Viaduct at Letchworth, NY - I’m not sure of the details, but the current speed limit over the bridge is much less than for the adjoining tracks.
When I next get near my copy of Design of Modern Steel Railway Bridges (by John F. Unsworth, P.E., of CPR, 2010, CRC Press), I’ll see what it has to say on the relationship of speed vs. impact loadings on bridges.
- Paul North.
NS announced yesterday that they are going to build a replacement next to the Portageville Viaduct next year citing increased traffic due to natural gas finds in the area.[:D]
What about over a livt bridge? Would it have a reduced speed?
Portage Viaduct had a 10mph speed restriction in place as much as 20 years ago. There’s a 10-degree curve near its west end. Plus a 0.66 percent descending grade approaching this curve and the bridge. Back when I used to visit that place, the majority of heavy trains moved east: big BUOIs, BUMEs, coal, long Hanjin and SeaLand stacks. Stuff you’d want to bring down to a crawl before hitting that combination of tight curve and high bridge with half your weight still coming down off the hill. And if nothing else, there’s the summer and autumn influx of visitors to Letchworth State Park who flock out onto the bridge. I saw as many as two dozen leaf-lookers up there one fall day.
Movable bridges will usually have a speed restriction because they are inherently less stable than fixed bridges. Also, there are gaps at the miter rails where the movable portion of the bridge abuts the fixed approaches.
Not always, CSSHEGEWISCH, there are no hard and fast rules in railroading. Every inch of track, every owner of track, every operator of track, every type of equipment, every infrasturcure, every condition, every day, every train type, every locomotive, every operating officer, everthing is different in each given situation. I know of lift bridges with 10mph and 65+mph, straight track at 5mph and 100+ mph, curves a 2 mph and 100+mph, etc. You have to read every railroads operating rules, instructions, and timetables to answer any given situation, equipment. and location and then check bulletin orders in effect that hour.
All of ours are 49mph.