Highway Underpass

[Bob Collins]

I'd like to cut a highway underpass through my subterrian riser but don't know how high I should make it. My riser comes 3" off the benchwork to the roadbed. Can I get the underpass in without having to come clear up to the track requiring me to build a trestle or install a bridge?

Bob

 

[shamus]

Hi Bob,
You should get the underpass in without having to come up to the tracks, at 3" clearance there is plenty of room.
Shamus

 

[Bob Collins]

Thanks Shamus, but to keep it as close to "scale" as possible, how high should the underpass opening be and how wide for a two lane road?

Bob

 

[Gary Pfeil]

I suppose it would vary with era and location, but 13 to 14' clearance seems reasonable, that would be about 2"in HO.

Gary

 

[Bob Collins]

Thanks Gary.

So, using your dimensions, if I made it about 2 1/4 " high and about 6" across I would be in good shape. I figure if it looks "too wide" I'll put a sidewalk on one side

Like buying a building so I could get a feel for sizing, I guess I need to get my hands on an HO scale vehicle or two, so I have a better grasp on how they fit too. I think I have a picture in my mind of something larger that what HO scale vehicles really are.

Bob

 

[justind]

a suggestion

A suggestion,
I have noticed that what they call "HO" scale vehicles actually differ a lot in size. Especially in Autocarriers (the cars there look more like "N" when compared against a typical "HO" car). And semi trucks (deisels) tend to be oversize. If I were you I would plan to make the underpass a little oversize just in case.

 

[Bob Collins]

Hi justind;

Thanks for your input. As I look at the situation I think I am restrained to keep at least a 1/2" away from the bottom of the roadbed, but on the other hand, since the structures sit on a 1/2" sheet of blueboard I could also take the underpass down to the benchwork too. That might look pretty cool and provide another change in elevation

I also think I will use some method to plaster the inside of the underpass which will allow me to paint it some grimy concrete color

Bob

 

[Gary Pfeil]

Bob, I am in the process of building a road on my layout, and have already gone thru the work of determining proper widths. I determined 1-1/2" per lane. I have laid in a base 5" wide, 3' for the lanes, 1/2" each side for shoulders, remainder for sidewalk, one side only. Actual road construction can be approached many ways. The only road I built previously was poured using Durhams rock hard water putty. I was very happy with it. My current project is using styrene. On top of the 5" base mentioned, I will glue 60 thousanths strip down the center of the road to provide a crown. I will use 20 thousanths material for the road (scribed for expansion joints, this is a concrete road). The sidewalk will be 60 thousanths, also scribed. One question: If you run a road under your tracks, don't you need a bridge of some kind?

Gary

 

[Bob Collins]

Gary;

There are many places I have seen where it appears that the road access under the tracks has basically been bored and there is no evidence of a bridge at all. Now there may be some sort of reinforcement that is not visable, but otherwise there is no evidence that the railroad recognizes that the road is even there. I have a very clear picture in my mind of a situation like this in west Omaha where there is a two lane underpass that passes under multiple tracks of the UPRR mainline. In this case I would guess that the distance from the trackage to the top of the underpass is about equal to that from the top to the bottom of the underpass, maybe 16-17 feet. I want it to look like there is no break in the roadbed/ballast and to do that I need as much distance between the roadbed and the top of the underpass as scale will allow. That is why I thought to take the highway down to the benchwork would improve the realism of the scene. That would actually give me about an inch between the roadbed and the top of the underpass.

Bob

 

[Gary Pfeil]

Bob, O.K., I think I know what you speak of. Just a guess, no one can accuse me of having any knowledge of construction, but the type of crossing you are planning usually has a "box" of sorts built from concrete, the top of which supports the track and fill. The sides of course are the walls of the underpass, the bottom the road itself. The height from track down to top of underpass can probably be as small as you want.

Gary

 

[Bob Collins]

Gary;

You are correct in describing the underpass I am thinking about, basically a concrete box. I have also seen them where they appear to be nothing more that half of a metal, corrigated drainpipe, but those are usually one lane jobs out in the hinterland somewhere.

My plan is to make mine look "concrete" so your comment about fitting it as close to the roadbed as I need helps a great deal in vitualizing and construction. I had thought about giving it a rounded appearance, but I think it will be easier to construct if I basically square everything off. It also gives me a little more latitude in the materials I use.. I don't have to bend or shape anything. Many thanks

Bob

 

[gibbs]

I agree with Gary's dimensions for roads. Typical lane widths vary from about 10' to 12' wide depending on their use (ie rural vs. freeway). As for clearance, today's standards are about 15' to 16' feet for modern 'bridges'. To round it off in HO scale 1.5" per lane and 2" to 2.25" clearance.
Again, these dimensions would apply for modern road applications in North America. I understand that in Britain, they use 10' wide roads for 2 lanes! (Just kidding! But after driving on some of those old country roads it 's not far off!)