On the Trinity Railway Express (TRE), which is a commuter railroad between Dallas and Fort Worth, TX, most of the line is now laid with concrete ties. However, there are several sections that have new wood ties.
The concrete viaducts just east of CentrePoint DFW have balast laid on the floor with wood ties. Why would they not use concrete ties on the viaduct?
Weight.
Thanks! Makes perfect sense.
If I remember corectly from an story on one of the railroads rebuilding projects, they used wood ties on a concrete deck bridge, because the concrete ties as they moved under use, could wear into the deck and damage the deck’s surface, wood ties would just wear the tie and not damage the concrete deck
Wood ties also provide more vibration damping than concrete ties which makes trains a little quieter.
I suspect concrete ties being significantly thicker (vertical dimension) has something to do with it as well. Would require more ballast depth (and that’s way more extra weight than the ties themselves.)
I watched, and photographed, a concrete bridge installation. After all the pre-stressed concrete sections were in place some type of fabric was laid then covered with ballast. Track panels with wood ties were then put in place and bolted together, and then tamped. Welders later came and made it CWR.
If there are insulated joints in the track structure, then wood is likely as well … but I suspect the main reason is shock absorbsion so the cycle stresses are not directly transmitted through the tie and into the structure without being disapated (then again, tie changeout on a bridge, any bridge, is a giant pain in the patoottie)
Almost all of the above reasons are valid for some circumstances.
Someone I met at an AREMA seminar a couple years ago asked a question about one instance in the Denver area where the overhead clearance for the light rail line was so tight - and there was something else underneath (maybe another rail line) - that to use concrete ties would have meant almost no room for ballast stone under them, thereby greatly increasing the ‘impact factor’ for the bridge loading, and hence its cost and complexity. They were struggling to shave inches off anyplace they could !
Another possibility may depend on how the bridge bearings/ supports were set up to deal with the CWR heat stress and forces. If the design concept/ intent / theory was to let the track ‘float’ a little bit - particularly for short spans - then the added weight and depth of the concrete ties to restrain the track from moving much at all would not be of any benefit.
My name is Ed Burns and am a retired NP-BN-BNSF clerk from Minneapolis, Minnesota. I was BN’s Twin Cities Terminal Roadmaster’s Clerk at Northtown from 1987 to 1990. Our office was at the Northtown Hump Tower. About 1989, the Roadmaster purchased about 20 or so steel ties for the engine rest track at the Hump Tower. He said that those steel ties would hold the gauge better then the wood ties they replaced. I don’t know how many steel ties there are in the Twin Cities on the former BN.
I am not a track expert by any means, but as I have learned during my times befriending track crews, contractors and operations personnel here is what I learned.
Wood had been very plentiful and cost effective, thus it was used. Wood would be used in places where environmental rot or bug damage is at a minimum. I have seen on tight curves in and around the KC area (BNSF “S” curve crossing the river into the yard steel ties). Best guess, steel was used along with the wood ties to keep the gage.
As technologies improved, costs came down, concrete ties replaced steel for the same properties and uses. Concrete can be used in the “wettest” climates as they do not rot. Yet, wood ties are still used where some give & take is needed for sections of track, where tie replacement might be difficult (limited clearances). I’ll see if I can email one of my UPRR or KCS friends and ask why wood vs. steel vs. concrete is chosen.
Diesel fuel will degrade timber ties faster than anything else except fire. Diesel soaked ties sitting in ballast fouled by engine sand won’t hold spikes or screws for long…and then there’s the Azobe tie.