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Half-height Overpass

Build in conjunction with half-depth underpass
  (+4, -1)
(+4, -1)
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This Idea seems so simply obvious that somebody somewhere should have implemented it -- but I've never encountered one, nor has some Googling turned up an example. So, be aware that this posting may have a short lifespan, until someone links to an existing baked version.

When constructing a highway intersection overpass, the engineers usually build two ramps of piled-up dirt (often with concrete erosion protection). Then they build the short bridge that connects the two ramps, so that one road goes over the other. Note that the piles of dirt had to come from somewhere.

When building a highway or street underpass -- usually under railroad tracks -- engineers scoop out a lot of dirt, and shore up the sides of the trench with concrete, so that autos can drive under the railroad tracks. Note that the dirt from the trench has to go somewhere.

OK, in the future, why not do both? At some highway intersection (this Idea is not for railroad crossings), dig a shallow trench for one road, and use the dirt to build lesser ramps for the other road's bridge. About the same amount of concrete will be needed, as in either of the two standard scenarios, but costs are reduced because there is significantly less total dirt (50%?) to move around (for no significant distance). The total vertical distance separating the two roads will be perfectly normal, yet autos will have an easier time driving through this intersection (climbing lesser ramp or climbing out of shallower trench).

Vernon, Jun 02 2004

King William Street underpass, Bayswater. http://www.watoday....0150619-ghs4jg.html
Sometimes called a bridge, sometimes an underpass. [AusCan531, Jul 21 2015]

King William St Aerial http://i.imgur.com/Gf3H60F.jpg
Shows tracks at ground level. [AusCan531, Jul 21 2015]

King William St Road Level http://i.imgur.com/343u4MR.jpg
Shows road going down. [AusCan531, Jul 21 2015]

[link]






       As you said .. sounds too obvious not to have been baked .. but until I read about it elsewhere .. have a bread-bite!
britboy, Jun 02 2004
  

       [vernon], this is the first of your ideas i have read from start to finish, and it makes a lot of sense.
Maybe i'll try reading another one (when i have some time off work!)
MikeOliver, Jun 02 2004
  

       Very smart +
phundug, Jun 02 2004
  

       The drainage for the lower road will have to be very good as it'll be prone to flooding in heavy rain.
oneoffdave, Jun 02 2004
  

       “That so many could have drowned after only a two-inch rain is unprecedented. Federal investigators say that they will get to the bottom of it, but preliminary reports indicate the design was by a young civil engineer, who, when questioned, would only admit that he was inspired by ‘Vernon’.”
ldischler, Jun 02 2004
  

       [oneoffdave] and [ldischler], yes, I am aware that drainage problems prevent many underpasses from being built. There should be more options here, since I'm specifying merely half-depth trenches. That is, I tend to think that wherever the water table will let a 3-meter-deep trench stay dry, then one of these intersections would be feasible.
Vernon, Jun 02 2004
  

       I say good on you! +
DesertFox, Jun 02 2004
  

       Day-old croissants and muffins could be used to absorb the excess rain water.
phundug, Jun 02 2004
  

       Getting the water out of the half-underpass would be a problem. So would getting a good view along the road ahead. The half-overpass would end up being low enough that it would partially obstruct your view into the distance until you began the dip to move under it. Also, there is a lot of dirt that needs to be dug up just to put in a road, I doubt they'd build that way if it were really in shortage.
PghArch, Jun 02 2004
  

       This was done recently when it was decided that traffic at a local railroad crossing was getting too heavy and backing up too much when the really long (and I mean really long - it takes about 20 minutes to pass) trains would go by. The road was closed for about a year while the underpass was dug out underneath and the tracks were shored up. Fortunately, it's right next to a river, so drainage is not a problem. Visibility, however, is a problem. It's a low-speed road, so it's not too bad, but it would be a serious issue on a freeway.   

       Also, if this were to be attempted on any major roads (i.e. freeways) it would cause huge traffic problems during construction. It's easier and cheaper to just build a pair of long ramps and a bridge over the existing road than it is to try to re-build the entire intersection.   

       Interesting idea, but baked where practical and avoided where not. So: no vote from me.
Freefall, Jun 02 2004
  

       Actually, I'm fishboning you here. It's true that, on the surface, you'd have less earth to move.   

       But the minuses are that you'd have to shut down the existing highway to reduce the level of the underpassing roadbed, AND you'd have to move more than just 50% of the normal amount of dirt in the end - high-speed roadways have much stricter grade requirements than slower, overpassing roads do: the angles of elevation can't be nearly as sharp as the ones on the slower road.   

       So you'd have to make the grade decrease and increase approaches much, much longer than the ones on the overpassing road - leaving you with excess dirt that you then have to dispose of somewhere.   

       Drainage is not that much of an issue - it'd be hard, but not too hard (just need a long pipe with gravel in it, and holes every so often).   

       It's not necessarily an original idea, as I'm sure it's been thought out before, but you're probably among the first to publish it on a grand scale. Definitely not baked for the masses.
shapu, Jun 02 2004
  

       //leaving you with excess dirt that you then have to dispose of somewhere// You're assuming you'd have to dig down as far as you would build up, which is not necessarily the case. There is a balanced solution, no matter what grade is required.
Worldgineer, Jun 02 2004
  

       See Vernon you came up with one idea that could work, or you could hold a dirt mound lottery. I'm sure someone wants to be a millionare in dirt. +
sartep, Jun 02 2004
  

       Nice idea, even if at occasion some engineer already stumbled over it. If this becomes standard it could worthwhile to contruct a robotic vehicle that does the dirt moving. All movements would be in the confined area of the construction site, so there would be little risk of hurting innocent bystanders. Perhaps NASA could set it as a challenge to test prototypes of Mars robots.
kbecker, Jun 02 2004
  

       I'm sure in limited applications this idea would be practical. I think in general though going over is just plain cheaper than digging a tunnel. No drainage tile to worry about, if one roadbed already exists you may not have to close it to build a bridge over it for very long, Lighting in tunnles can be a problem, and Moronic teenagers tend to hang out in them. Most overpasses around my town avoid much dirt moving at all, The overpass is just proped up on concrete pylons. Pigeons nesting underneat the roadbed is the bigger problem for cars underneath.
tedhaubrich, Jun 02 2004
  

       [PghArch], the need for a long view ahead depends on the type of road and the type of underpass. A simple two-lane street would probably be marked to forbid passing in the underpass. Wider multilane roads usually don't have that problem with respect to oncoming traffic, and so you can confidently travel the underpass at full rated speed.   

       [Freefall], Regarding construction, I wasn't really implying that this kind of intersection suddenly needed to pop up everywhere in existing traffic patterns. However, where an overpass is needed, as you noted, building any sort of variation on the theme involves traffic congestion. But consider the notion that moving less dirt for this kind of intersection means it can be constructed faster. Then consider that logistically, the thing to do first is build a temporary steel ramp and overpass -- something that can later be disassembled and moved between sites. Then work on two narrow side-trenches begins, so that the future concrete retaining walls can be poured even before the main trench is dug. If done one at a time, then only one lane of traffic need be closed at a time. Next, the dirt from this and from the main trench can begin to be piled up underneath the steel ramps. Each time the earth-scraping machines make a pass through the intersection, then traffic can flow until congestion is relieved enough for the scrapers to make another pass. Toward the end there will be dirt in a pile nearby, waiting for final "packing" into the ramps. Meanwhile, forms for concrete, for the sides of the overpass ramps, can be prepared without affecting traffic. When the underpass is all done, the lowest-level portions of the steel ramps can be removed, packing of dirt can take place, and paving can be done. The construction crews work their way up the ramps, until the actoal overpass can be replaced with prefabricated sections that are helicoptered in. Done! Finally, regarding "baked", can you specify an example?   

       [shapu], [Worldgineer] is right, that no matter what grade, or even PAIR of grades (if different for overpass than underpass) there is an optimum solution, a particular depth-of-trench, in which the dug-up dirt is just the amount needed for the ramps. FINDING that solution probably involves nothing more complicated than a combination of trigonometry and algebra (volumes of appropriately scaled wedges).   

       [lurch], your description doesn't really indicate that the dirt dug from the no-doubt-FULL-ordinary-depth underpass was completely used as ramp material for that highway. I tend to think that there was probably some excess dirt when they were done. Also, I got the impression that "they had to do it that way", yet didn't see any advantages in deliberately doing something similar at another location. It's like they didn't realize the full scope or possibilities of what they had done.   

       [tedhaubrich], a low bridge is still a bridge, and the underpass beneath it does not qualify as a tunnel.
Vernon, Jun 03 2004
  

       I live in Derby, UK and this is baked in our city centre.
david_scothern, Jun 03 2004
  

       [Zanzibar], this Idea is NOT for railroad crossings. Rail tracks have to be rather level because trains can't climb steep grades. So full-depth underpasses are built (and will continue to be built, along with the occasional full-height overpass) when they don't want traffic and trains to meet. Regarding drainage, I did state in my first annotation that this Idea is not for every location, due to water-table considerations. Where it IS feasible, all that the underpass needs are drains and culverts leading to a standard drainage ditch.   

       Folks, please keep in mind that because the underpass here will be much shallower than usual, serious floodings and drownings will automatically be less likely. And remember that in spite of all the drownings that have occurred in the past at full-depth underpasses, they continue to be built!   

       [BrauBeaton], yes, this Idea is mostly for flat areas, where overpasses-only are the norm. I do know that in hilly areas it is normal to "balance" the terrain when road-building.   

       [david scothern], can you provide more information (a link perhaps)? If really baked, I don't mind leaving this up for a week or two, then deleting it. Thanks!
Vernon, Jun 03 2004
  

       Having worked in the road construction industry for a while, I'd estimate about 60-75% of our over passes are constructed this way. Drainage at on the under-pass isn't usually a problem because the sewer system is still lower than the dip of the under-pass.
SystemAdmin, Jun 03 2004
  

       [SystemAdmin], thanks, but WHERE are these things being built, that so few here have seen them?
Vernon, Jun 03 2004
  

       Since nobody deigned to link an existing example in all the years since this Idea was posted, I shall assume that it was neither widely-implemented nor widely known, and no longer see any need to think about deleting this post.
Vernon, Jul 16 2015
  

       And so saying, he left in a half.
MaxwellBuchanan, Jul 16 2015
  

       Somewhere in the vicinity of Chamonix, France, there is a partial road-cycle path under-overpass. You can ride under the road easily. You can even go quite fast. Not very fast however, there's still a bit of my scalp on the bridge.
bs0u0155, Jul 16 2015
  

       + They are using the tons of dug out limestone from the railway, waterworks and car tunnels to Jerusalem, as landfill for the elevated overpasses, on the new road construction to Jerusalem and Bet Shemesh.
pashute, Jul 18 2015
  

       This generally done in the UK, or at least it's done at a fair proportion of overpasses.   

       In general, it's less often done when a minor road has to pass over (or under) a motorway. In these cases, the major road is kept on the level, to better deal with fast traffic; also, the smaller road generally requires less work to raise (or lower) than the big road does to lower (or raise).
MaxwellBuchanan, Jul 18 2015
  

       //In these cases, the major road is kept on the level, to better deal with fast traffic; also, the smaller road generally requires less work to raise (or lower)//   

       If you replace "major" with "canal" or "river" it's always true... must be something to do with the speed of canal boats, no one wants to hit a hump back bridge while screaming along at 3.7 mph in a 70 footer.
bs0u0155, Jul 21 2015
  

       The main problem with hump-backed canals is getting the horses to pull the boat uphill. Then, on the other side, there's the risk of the boat running away with them.
MaxwellBuchanan, Jul 21 2015
  

       //The main problem with hump-backed canals is getting the horses to pull the boat uphill//   

       The answer's obvious. When the canal goes up, make the towpath go down. The horses will find it easier handling the weight with the help of a down slope. Then simply reverse the whole process for the other side, the horses will appreciate the boat helping them up the hill. The net height change is the same for both, so it all works out OK.   

       A less obvious solution might be the development of a hybrid horse with regenerative braking. On downhill sections, the horse vomits up a combination of hay, sugar lumps and oats into a nosebag. The process is reversed for uphill sections. I would not be at all surprised to discover a Toyota-Barbour collaboration project trying to get this one off the ground for the horsey crowd.
bs0u0155, Jul 21 2015
  

       //hump-backed canals//. SP: hump-backed camels.   

       There is a bridge/underpass built like this in Perth [link]. At least 3 times per year a truck gets stuck under it blocking traffic for the day. During heavy rains it floods to over a metre deep. It is not a favourite design for the locals.
AusCan531, Jul 21 2015
  

       //During heavy rains it floods to over a metre deep//   

       This is where the canal comes into its own. The remarkable absence of times when it is not raining heavily led the North West of England to build a whole transportation network based upon the principal.
bs0u0155, Jul 21 2015
  

       Regarding that linked King William Street underpass, a rail bridge over a roadway is never any significant degree of climb for the train. This Idea is specifically about a 1/2 height overpass and a 1/2 depth underpass, both relative to ground-level, although only the first part of that made it into the title. Approaching the intersection at ground level, traffic in one direction goes up a little ways, at the intersection, and traffic in the other direction goes down a little ways, at the intersection. Why is that simple thing getting misinterpreted?
Vernon, Jul 21 2015
  

       Hey there [Vernon]. The 2 new linked photos might make it clearer. King William St has a 1/2 height overpass and a 1/2 depth underpass, both relative to ground-level although naturally the rail has a gentler incline than the road.
AusCan531, Jul 21 2015
  

       [AusCan531], if the ground is not level, trains often have raised rail-beds (or a trench is cut) to keep the tracks level. It looks more to me like your intersection goes deeper into a natural dip in the terrain, than the train is made to do any climbing as it approaches the intersection.
Vernon, Jul 22 2015
  
      
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