Well, not all railroad crossings.
But still, it seems like more often than not, when a road crosses a railroad track, the area around the rails that auto traffic will drive over is filled in with wood (I’d guess railroad ties).
Is there some reason for this?
I think to keep the area as flat as possible, while still giving the train the needed grooves to stay on the track. Train wheels only need grooves inside of the tracks, so wood anywhere else shouldn’t hurt them and make it smooth enough for a car to cross.
Unless you’re talking about why they use wood instead of just using metal? They do this too at some crossings.
This must be a US thing, because I don’t remember seeing crossings like that. Here, they are filled with bitumen (or whatever goop that particular road is using, might be concrete too) held back with a checkrail or metal bar to keep it in place and to provide a gap for the flanges (a checkrail is the third and fourth rail you often see on railroad bridges to contain derailments).
Perhaps the thinking is that the wood can be placed in there slightly loose to allow for expansion and contraction with temperature without moving the rails or impinging on the flange groove. Also, fixing a pothole in the bitumen wouldn’t be like fixing one elsewhere - they’d have to shut down the railroad for what is really a tiny job, so the wood might be more maintenance free, only coming at the tiny expense of a budububduabada under your wheels as you drive across; useless for regular roadbuilding, but good at crossings.
Also, the maintenance of the crossings is the responsibility of the railroad track gangs. They have lots of railroad ties on hand. They don’t usually keep paving materials handy.
Former railroader here; never worked in the maintenance-of-way department, but can, I think, infer most of the reasons for the (declining) use of wood on US railroad crossings. Firstly, the track structure ‘floats’ on a layer of ballast and flexes under the weight of a train, so on a heavily-used line, the asphalt (or sometimes concrete) fill on a crossing would frequently break down and need repair. It’s not so bad for a lightly-used branch or spur, but most of the worst crossings I’ve traversed were asphalt-filled: the paving tends to hump up on either side of rails, and potholes seem to develop quite easily.
So far as I know, the timbers used in wooden railroad crossings are not in fact railroad ties but are specially cut for the purpose, as a standard wooden tie laid on top of the crossties between the rails would stand higher than the railhead. The wood holds up better under road traffic and has some ‘give’ when the track structure flexes under the weight of a passing train, but variations in height among the parallel timbers, and the bolts or screws that hold them in place, cause a notably rough ride for cars and trucks. For that reason, wood is falling out of use for this purpose; most new or rebuilt crossings these days are covered with a set of rubber-like mats, that provide a much smoother ride for road vehicles. Most of these crossings can be taken at normal speeds with little more than a light bump as the tires cross the railheads.
Wood was “always” used because it was plentiful and cheap. Lately, though, the wood had oftern been replaced with more durable rubber or composite material. I drive across one an a US highway that has had its rubber fillers replaced with precast concret slabs because of the rubber needing continued maintenance/repair. BTW, a hundred-plus-year old agreement between the railroads and my state says that the r.r. is responsible for repairs within 12 inches of the rail. Further than that, it is up to the state or local road agency. Replacement cost of the entire xing is shared 50/50 usually. I used to write purchase orders for the local share of annual maintenance costs of the r.r. xing signals and gates/flashers in that city.
FWIW, according to my railroad expert at work, El_Kabong is pretty much 100% correct.