Can anyone tell me the pros, cons and other important factors that influence any given railroads decision to use treated-wood, concrete or composite technology rail ties in the roads?
cost.
Like the man said, cost is right up there as a consideration.
Wooden ties tend to be resilient - a rolling derailment (one that doesn’t physically tear up the track) usually just leaves marks on the ties, whereas concrete ties may crack and have to be replaced.
I haven’t seen much on composite ties - I suspect they’re still in the experimental stage.
Wood ties tend to deteriorate over time, which is why you’ll see them being replaced (often wholesale) fairly often on busy lines (although we may be talking tens of years here). On little used lines the mud (ballast often being just a suggestion) is sometimes doing more to hold the track in guage than the ties.
I’m not sure that I’ve heard the life expectancy of a concrete tie in normal use.
I’m sure MC, RWM, and others will give us the lowdown soon enough.
The Simmons Boardman Track Cyclopedia deals with these and many other issues. Published by the same folks who put out the better known (and more often seen at swap meets) Car & Locomotive Cyclopedia. I think the most recent edition is 1985. I bought the 1970 edition at a swap meet. I also have a much older Railway Engineering and Maintenance Cyclopedia. I paid a pretty penny for both but the info is worth it.
Dave Nelson
For new construction on a busy main line, concrete ties are very common. They do provide a more stable track structure. In general, though, the railroads do not mix concrete and wood ties, so for normal replacement of tired wood ties they are replaced in kind. Some high-traffic lines have been upgraded with all concrete ties, but the cost is high. As well as the higher cost of the concrete ties, a lot of life of the wood ties taken out is lost. Some will be reused elsewhere but others, which might still have a few years of life remaining, are just not good enough to be worth the trouble and expense of handling.
Concrete ties are very heavy and need mechanical equipment to handle, unlike wood ties which can be replaced by manpower and simple tools. If trhe choice is to switch to concrete ties, the necessary equipment must also be provided to the local track gang.
This is a long-winded way of saying “cost”. In certain cases, mostly the very heavy tonnage lines, the cost is justified.
Under heavy tonnage, wood ties, especially softwood, will deteriorate much faster than on a branch. Concrete ties are not necessarily trouble-free either. There have been some issues with rail seat abrasion, where dirt gets under the rail and starts wearing down the concrete underneath. This has resulted in at least one derailment. Early designs of concrete ties derived from European practice and did not withstand the higher axle loads over here very well. Redesign of the reinforcing around the rail seat has mostly solved that problem.
Composite technology is still largely experimental. Nobody wants to make a huge commitment to a new product without some certainty that the working life will be competitive with the known 30-50 year life of current ties. The labor cost to replace ties prematurely is not cheap (there’s that word cost again).
John
The CTA in Chicago is making heavy use of compositie ties on its rapid transit lines.
In addition to the above -
Weight, and stability against buckling, esp. for CWR in hot weather conditions. Track = rails, ties, and fastenings [‘OTM’ for ‘Other Track Materials’] will weigh around 200 lbs. per track-foot for 130 lb./yd. rails and 7’’ x 9’’ wood ties [not including the ballast]; for concrete tie track, with 800 lb. ties at 30’’ spacing, the weight will be about 400 lbs. per track-foot, or about double. However - where there’s an old structure - such as a bridge or ‘elevated’ in a passenger or transit system, where the ‘live’ carloads are not as high as on a freight railroad, and the ‘dead’ load of the track is more significant, such as on open-deck structures’ - then that additional tie weight may add too much to the dead load, and so preclude the use of concrete ties. That may be why or favor CTA’s use of composites.
As a result - plus the fact that the concrete ties tend to sit deeper down in the ballast and have more like 4 times more weight bearing on the ballast under each one of them than for wood ties - concrete tie track is far more resistent to heat-induced buckling. Concrete tie track is also usually ‘tighter’ in the rail fastenings than wood ties, so there is less ‘slop’ to allow the rail to move even small amounts, or to start to buckle.
Concrete tie track is also slightly stiffer in the vertical plane, and so spreads the train loads over a slightly larger area, reducing pressures on the soil underneath. But concrete tie track is not as forgiving of soft or otherwise poor soil conditions - esp. not ‘center-binding’ - so it is not as good there.
Rail-to-rail insulation in electrified operations - such as transit agencies - or for signal circuits may favor wood and composite ties over concrete, esp. in moist, wet, or occasionally inundated locations.
Track that is often covered in mud or vegetation, or water -
I bought a Kindle book on my iPod Touch about military railway maintenance. It was rather sloppily digitized. I am unsure of its printing date, but they talk about the Penn Central, so it is circa 1968-70 or so. It asserts that the use of creosote preserved ties gives up to fifty years of service. The use of concrete ties, in the time of the early 1970s, was cost prohibitive, but was asserted to be up to 100 years service. The fifty years of service for creosoted ties caught my attention, but keep in mind this was a field manual about military railroad maintenance.