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Notes/Instructions - road profile, bridge clearances

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    Notes/Instructions - road profile, bridge clearances

    This will be a long topic. I want to explain how I lay track from track charts, roads fairly accurately, set clearances for bridges over the track, and other items.

    Tools: You will need a calculator, writing instrument, Google Earth, Topomaps, kml-mkr converter and lots of scratch paper.

    Track: You can buy, mostly from Ebay, track charts of most railroads. Railfandepot was a good source but it has been moved to Ebay. Most track charts do not provide elevation above sealevel so you need to get that from Topo Maps. You can find these by doing a google search but I use the USGS source for mine. Once you find the map you want, if there is a .kmz file of it available grab that as well. I have found that existing track can usually be traced off of Google Earth easily and in doing so you create a path file in the column to the left. When you stop digitizing, save this file as a .kml file so that you can use the kml-mkr converter to create a marker file that will make points in the route file to track the track with. As I am doing this, I also note road crossings, bridges, turnouts, tunnels, etc. and write down the coordinates for those. Note that the gradients shown on a track chart are "Usually" compensated gradients, i.e. the grade is increased slightly if curves are present. Because of this, it is desirable (but not very accurate) to find the apex or low points in a grade as to get things really correct, you may have to reduce the published grade just a little. I find track to be rather easy to lay, but roads, that is another issue.

    Roads: We only have a limited number of curve values in roads so it is not likely that we can get a road precisely correct, but we can get close. In digitizing both track and roads, I make my elevation points, i.e. apex or low point, in meters. In making linear measurements with Google Earth, I use feet. Burn the constant 3.28 in your brain. I start at one end or the other of my digitized path and I lay a piece of road that is long enough to reach from the first point to the 2nd point which are hopefully in a tangent. If I hit the "R" key, I can use the mouse to roughly align this piece to the first two points. Then I will use the rotate about "Y" function in transform to rotate the piece tiny amounts until it is aligned. Then I will raise of lower the piece to the elevation found on the topo map, or Google earth. Since this will be in meters you should have converted the elevation, if in feet, to elevation in meters. Well, remember 3.28---. Lets say you have an elevation on the map of 328 feet, okay, divide by 3.28 and you have 100 meters. Next, slide the mouse along the digitized road and notice the changes in elevation in the lower right area of the screen. If it is increasing and then starts decreasing, you are close to an apex, or high point. Locate that, convert it to meters, and jot down this data & the coordinates. Also put a pushpin at the location with the elevation value on it. Like this, for that 328 foot point, I will have a value of 100 meters. (Marker (-84.5710 36.3677 E-100M 2 ) ) I make a simple line chart on the scratch paper and put the elevation points on it for several spots. Then, using Google Earth, I measure The distance between points in feet. I subtract the low point from the high point in meters, and multiply the result by 3.28. Thus having the difference in feet, I divide by this measured length to get a value very close to the actual gradient & I use that to lay the road between the points.

    After I finish doing this for a road section (this fictitious location would be near Oneida, TN) I use the Context editor to key in the values. With those values and with the result of the digitized path in the marker file, I will have a string of marker flags with elevation values mixed in. If we did not have to be concerned with roads intersecting tracks this would do, but alas, such is not the case.

    Crossings: I find it easier to start a road section at a crossing and use the alignment method above to position the piece accurately as to crossing angle. Although the track may have a gradient, the part of the road across the track usually does not, so if the road is on a grade, this piece needs to be as short as possible. Once it is in position, you can then follow the digitized route to lay the rest of the road.

    Clearances: This got to be a real issue with the advent of double stack trains. Double stacks require at least 27 feet (8.23 meters) between the rail head and the underside of whatever kind of bridge is involved, or the roof of a tunnel.. If double stacks are not involved, then 20 feet is sufficient (6.1 meters) As general rule, I use 10 meters as my minimal clearance just so the math is easier. If you have already shaped the roadbed of the track, then just put the mouse on the surface of the track below where the bridge is to go and read the pointer "Y" value on the navigation panel of TSRE which will be in meters. If the bridge is concrete, like a road bridge, then I would add 2 more meters to this clearance value. If it is some kind of truss structure or a plate girder span for another railroad, then you should add the vertical dimension value of the bridge. A bridge engineer in the long ago at CSX told me that a 1:10 ratioin length & height is the rule of thumb. Thus if it is a 80ft. deck plate girder span, you would need another 8 feet (2.44 meters)

    This is just meant to be a "getting started" help and you will probably find your own method. If it works for you, then use it.

    Jerry Sullivan (aka landnrailroader) (retired from CSX, SOU, and as a docent on the C&TSRR)

    #2
    Thanks Jerry, if you got more helpful tips on route building...keep-em coming

    Comment


      #3
      Originally posted by landnrailroader View Post
      Double stacks require at least 27 feet (8.23 meters) between the rail head and the underside of whatever kind of bridge is involved, or the roof of a tunnel.
      There's a setting in TSRE to help you with this --- wireLineHeight = 8.2

      The yellow line height can be set to anything -- above shows the 8.2m doublestack clearance, but you could also set it to 6.7m to represent trolley wire. When setting the overhead object, as long as you can see the yellow line isn't interfering, you know you have your overhead clearance for the rails.
      If you like what you see here at Trainsim.com, be it the discussions and knowledge in the forums, items saved in our library or the ongoing development of our TSRE Fork, I hope you'll consider a paid membership to help support keeping the site operating.... Thanks!

      Comment


        #4
        Eric,

        You are half correct and I failed to point out a critical issue. Your method will work for the underside of bridges or just about any situation EXCEPT tunnels. In many areas of the country, tunnels had to be "notched" to allow double stacks. The root of a tunnel would be the top of the arch, and in the case of a single track tunnel, the top of a double stack would be dragging on the curved portion of the tunnel just about where the vertical side wall ends, and the arch begins. This is called the spring line. Check photos of tunnels on such places as the "Pokey" or the "Magnolia Cutoff-B&O) and you will see that the notch starts in line with the side wall and extends vertically into the arch at least 2 feet. This allows for sway action as well. So to use the wire height as a measure of the tunnel height, I would add 1 meter to the number, or 9.2 which is equivalent to 30 feet. If you use 27 feet, then your top containers will get rounded corners at the top -- not good.

        Jerry

        Comment


          #5
          Grade changes for track laying.
          Always go with a smooth transition.
          I typically use 10m pieces, but some cases call for 15m or even 20m, and then it gets more fun when it comes to curves and the changes.
          Anyways, always take it .1 at a time, so start off with .1, then .2, .3, .4, etc until you get to your desired grade, this of course, is mainline mostly, customer tracks and industrial tracks can be a bit quicker with grade changes.
          This will give a much smoother transition, versus the tired some old MSTS RE/TSRE quick tab of the incline which gives I think .3 or .4 changes at a time, however, also beats a lot of routes I have simply deleted over the years, due to going from 0.0 flat service, straight to 1.2 in one quick 10m or even 100m piece. Yikes.

          That is all I can really give for advice of track grade changes. I have more tips and tricks at home on my laptop.. but I don't want to totally take over Jerry's post..

          ​​​
          -Shawn K-
          Derby Rail Shops
          Maine Central Mountain Division: 25% Track, 12% Scenery.

          Comment


            #6
            For grade changes on the track, I sometimes use 5M pieces if the change is dramatic and the space is short. Otherwise I use 10M. Grade changes on the road can be a lot more dramatic and I will often make a 2% change between 2 pieces, straight or curve. And while the maximum track grade is about 2.2% unless you are doing Saluda (4.7%) or something like that, a 10% or greater grade would not be unusual on a highway.

            On another subject, lets remember the folks in the southern Appalachians that are in a world of hurt. Chimney Rock, NC appears to be wiped out and the EB lanes of I-40 along the Pigeon River are GONE. Along the Toe & Nolichucky Rivers, the former Clinchfield is under several feet of rushing water. That is a scondary CSX route and it is conceivable that it might not be restored. I have a lot of trash in my yard and in the valleys of my roof but no damage. My wife and I are picking at the trash and our son-in-law will be over to help tomorrow. Our yard service will blow down the roof for a fee which they will get on Wed. or Thurs. when they service us.

            Jerry

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