How common are these? The only one I know of is in Blum, Texas, on an old railroad bridge. The rail line was rerouted so as to lose less elevation and go over a higher bridge before Whitney Lake was built. This bridge became a road crossing over the Nolan River. This seems like it might be fairly common when a rail bridge becomes a back road, but I don't know of many of those.
http://goo.gl/maps/CXhpc (http://goo.gl/maps/CXhpc) You can't see the road all that well, but it's a gravel road with some moderate sized holes (pits, not all the way through), so you have to go slow. You can't cross with someone going the other way.
Probably pretty rare because the sides and bottom of the bridge need to be solid to hold the gravel. Rail bridges especially don't usually have a solid bottom, since only the rails support trains.
I can't think of any offhand. most bridges on otherwise gravel roads have the driving surface made of concrete. I've occasionally seen steel bridges with a steel grate to drive on, but those usually are concrete surface as well.
I've seen a few, but they typically aren't by design, it is simply the gravel working its way onto the bridge with the traffic. Of those I've seen, most were in Indiana on the county roads, and many of the bridges were made of wood. There was one or two where it was a concrete bridge that used to be a main road (usually a State Road) but has since been downgraded due to a new alignment.
Am I correct in assuming that the OP is asking about bridges where the running surface on the structure itself is gravel, and not about bridges where the road on either side is gravel but the deck has a surface of some bound material like concrete or asphalt? Bridges of the latter kind are very common as Interstate overpasses in farming country in Kansas.
Quote from: J N Winkler on January 06, 2014, 11:46:42 AM
Am I correct in assuming that the OP is asking about bridges where the running surface on the structure itself is gravel, and not about bridges where the road on either side is gravel but the deck has a surface of some bound material like concrete or asphalt? Bridges of the latter kind are very common as Interstate overpasses in farming country in Kansas.
bridges of the latter kind are very common, period. it makes sense to have this be general practice when building a dirt road on which bridges are required.
QuoteHow common are these? The only one I know of is in Blum, Texas, on an old railroad bridge. The rail line was rerouted so as to lose less elevation and go over a higher bridge before Whitney Lake was built. This bridge became a road crossing over the Nolan River. This seems like it might be fairly common when a rail bridge becomes a back road, but I don't know of many of those.
http://goo.gl/maps/CXhpc You can't see the road all that well, but it's a gravel road with some moderate sized holes (pits, not all the way through), so you have to go slow. You can't cross with someone going the other way.
wxfree, thanks for sharing this! Neat find, and very strange.
Here's a gravel surface bridge on OLD ROUTE 66 in New Mexico:https://maps.google.com/maps?ll=35.123594,-103.145442&spn=0.000035,0.024912&t=h&layer=c&cbll=35.123594,-103.145442&cbp=12,0,,0,0&z=16&photoid=po-22525060 (https://maps.google.com/maps?ll=35.123594,-103.145442&spn=0.000035,0.024912&t=h&layer=c&cbll=35.123594,-103.145442&cbp=12,0,,0,0&z=16&photoid=po-22525060)
Quote from: agentsteel53 on January 06, 2014, 12:03:04 PM
Quote from: J N Winkler on January 06, 2014, 11:46:42 AM
Am I correct in assuming that the OP is asking about bridges where the running surface on the structure itself is gravel, and not about bridges where the road on either side is gravel but the deck has a surface of some bound material like concrete or asphalt? Bridges of the latter kind are very common as Interstate overpasses in farming country in Kansas.
bridges of the latter kind are very common, period. it makes sense to have this be general practice when building a dirt road on which bridges are required.
While "very common", it seems to not be "general practice" even if it should be (and I'm not sure of that, covering a deck with dirt or gravel just for a uniform road surface seems not worth the effort). For some mostly unpaved highways, bridge decks are the
only respite from potholed dirt/gravel surfaces on the rest of the road.
https://maps.google.com/maps?q=Mililani+Town,+HI&hl=en&ll=21.45188,-157.990335&spn=0.001545,0.002642&sll=34.153007,-118.465544&sspn=0.003886,0.005284&oq=millilan&t=h&hnear=Mililani,+Honolulu+County,+Hawaii&z=19
Here's a dirt road bridge in Hawaii crossing the H2 between Mililani and Ka Uka Blvd.
Quote from: PColumbus73 on January 06, 2014, 12:24:07 PM
https://maps.google.com/maps?q=Mililani+Town,+HI&hl=en&ll=21.45188,-157.990335&spn=0.001545,0.002642&sll=34.153007,-118.465544&sspn=0.003886,0.005284&oq=millilan&t=h&hnear=Mililani,+Honolulu+County,+Hawaii&z=19
Here's a dirt road bridge in Hawaii crossing the H2 between Mililani and Ka Uka Blvd.
Have you driven on the bridge? I haven't, but from the aerial shot it's not entirely clear that the bridge has a dirt/gravel surface, rather than a concrete surface partially covered by a thin dirt/gravel coating picked up and deposited by vehicles crossing the bridge. Alas, Street View doesn't cover the road crossing over the freeway.
EDIT: The bridge in question is called the "Pineapple Road Separation" in HDOT's straight-line diagrams, and a local street atlas calls the road "Plantation Road". Sounds like the road is/was a private farm road, with HDOT maintaining only the bridge structure but not any road surface that may have been added to it.
Quote from: oscar on January 06, 2014, 12:36:20 PM
Quote from: PColumbus73 on January 06, 2014, 12:24:07 PM
https://maps.google.com/maps?q=Mililani+Town,+HI&hl=en&ll=21.45188,-157.990335&spn=0.001545,0.002642&sll=34.153007,-118.465544&sspn=0.003886,0.005284&oq=millilan&t=h&hnear=Mililani,+Honolulu+County,+Hawaii&z=19
Here's a dirt road bridge in Hawaii crossing the H2 between Mililani and Ka Uka Blvd.
Have you driven on the bridge? I haven't, but from the aerial shot it's not entirely clear that the bridge has a dirt/gravel surface, rather than a concrete surface partially covered by a thin dirt/gravel coating picked up and deposited by vehicles crossing the bridge. Alas, Street View doesn't cover the road crossing over the freeway.
I've never driven across it. I do agree that it's hard to tell if it's really dirt or concrete stained by Hawaii's infamous red dirt.
Very interesting; it seems it's somewhat rare. I've been under that bridge - to see the river, not so much the bridge itself. I didn't think to get a look at its construction. I'll have a look at it sometime.
The bridge wasn't urgently needed, as all it does it give a few people who live along the road a way into town that's a few minutes shorter. I suppose that since the abandoned bridge was there it just made sense to use it.
I'll have a look at the bridge sometime, but if I were to guess as to why it's a gravel road, I suspect that they pulled up the railroad cross ties and put down plates on the beams to make a solid bottom, and then piled up road material to level it out. Or perhaps the bridge had an unusual design and already had a solid bottom and they buried the cross ties in gravel to make a driving surface. Blum's the kind of place with a lot of old-timers, so someone might know.
Quote from: wxfree on January 06, 2014, 02:58:07 PMthe bridge had an unusual design and already had a solid bottom and they buried the cross ties in gravel to make a driving surface.
what would be the design impetus for such a thing? the solid bottom would just add weight without being efficient in bearing a load, no?
Quote from: agentsteel53 on January 06, 2014, 03:22:51 PM
Quote from: wxfree on January 06, 2014, 02:58:07 PMthe bridge had an unusual design and already had a solid bottom and they buried the cross ties in gravel to make a driving surface.
what would be the design impetus for such a thing? the solid bottom would just add weight without being efficient in bearing a load, no?
I don't know if it would have been built like that; I'm just guessing as to how it ended up this way. I've been on and studied wooden rail bridges, but not ones like this, with a steel beams and concrete columns. I'm surprised I didn't take a stronger interest in the bridge and study it when I went under it. I don't remember if it has multiple steel beams that run the length that cross ties would have been put on, or if the edges of the bridge are the beams with short ones running between to hold up the tracks. This isn't far from places I go regularly, I'll definitely want to climb under again and have a look.
Bridges with a cement driving surface are slowly replacing the older bridges that have a wooden plank driving surface that are (or used to be) typical for gravel roads in Central and North Central Texas. The bridges with a cement driving surface tend to have guard rails where the older wooden ones usually did not.
Hey! We have those (old wooden bridges) here too!
I went and had a good look at this bridge. The weight is held by the two beams along the sides, the tops of which now serve as guardrails. On the underside there's a cross member between the beams about every 10 feet, and these hold smaller beams that run length-wise. The 10-foot beams are steel, except the one on each edge; those are wooden. I'd guess that the cross ties were set on those beams, and nailed to the wooden ones. There's now a deck of wood planks, approximately 4 by 10, and the gravel is on top of that. The gravel is held in by a 4 by 10 on each side with the 10 inch side vertical, so the gravel's about 10 inches deep. This leaves a gap on the edges to allow drainage. The pile of gravel on the west edge is covering a pipe, probably to keep vehicles from damaging it, and maybe to insulate if it's carrying water.
This is an interesting redesign. I'm going to have to look for more old railroad bridges now used for roads.
QuoteI'm going to have to look for more old railroad bridges now used for roads.
Carpenter's Bluff- spans Red River between TX and OK. Not gravel surface, though.
Quote from: Brian556 on January 11, 2014, 12:29:51 AM
QuoteI'm going to have to look for more old railroad bridges now used for roads.
Carpenter's Bluff- spans Red River between TX and OK. Not gravel surface, though.
Thanks for the tip. There's one near Clairette, too. I've been over it once. I saw the rickety old road bridge to the west and realized it was a re-purposed rail bridge. The Panoramio picture makes it look like it has a concrete surface. I'm sure I'll have occasion to see it again. I don't go Denison-way too often, but the Panoramio pictures of the Carpenter's Bluff bridge suggest that when I do, I'll have to make a small side trip.
Another former railroad bridge: http://bridgehunter.com/il/lawrence/st-francisville/
If gravel roads on bridges than there should be appropriate signs that will help the people about danger ahead. I also need to decide speed limit on these types of bridges so that it help help to control risk.