Roadway Modeling for 3D Machine Control - Templates

Written by Ron Ciccarone, LS

Created on Sunday, 07 October 2012 11:19

In my previous articles on highway modeling, I covered initial issues and alignments.  In this article, we will deal with templates for DOT highways.

A roadway template explains what happens to the right and left of the baseline (or attachment point) as you would proceed down the alignment.  I have inserted a typical template from a set of highway plans.

Figure 1 - Note: to view the images associated with this article, CLICK HERE.

Let’s break down the issues and information shown in this typical template.  This is a very standard template with median, curb, paving, shoulders, side slopes, ditches and tie slopes.  I am making an assumption that your software allows you to build your roadway by templates and transitioning between the different templates.

Figure 2 - To view this image CLICK HERE.

The first thing to make note of, is the station ranges where this template will be used.  This particular template will only be used between the station ranges listed next to the template.  That means other templates will be used and transitioned to behind and in front of this one.  Making these transitions to work smoothly can be quite a challenge.  You will also notice that there is a note that there is a detail for intersections.  I will address this later in this article, because the intersection detail caused a big problem.  (But that is why we are paid the big bucks)

Figure 3 - To view this image CLICK HERE.

In Figure 3, the template shows where the centerline baseline is located and where the template attaches to the vertical profile.  In this case the profile defines the inside edge of pave on the left and right side, while being controlled horizontally by a dimension from the centerline that VARIES.  I love it when you see this word, now I have to go somewhere else in the plans to see what this dimension really is.  However, it may really be define in another set of plans like the paving plans or the cross-section plans.  This is one reason I prefer developing sites and subdivisions, it may be wrong, but it is all there!

Figure 4 - To view this image CLICK HERE.

In figure 4, let’s define the template parts.  From right to left, first there is a median curb and slope.  The median slope is projected back from the top of curb to intersect with the median slope coming from the other side.  Remember, the distance from the back of median curb on the left can be different from the distance to back of median curb on the right, it VARIES.

Next is the paving, which is 24’ or two - 12’ sections of pave.  I usually run this as two separate 12’ sections, but that is just how I build my DTMs.  It gives a line of points down the paving joint.

Figure 5 - To view this image CLICK HERE.

Then the shoulder is defined Figure 5, which can be one of the trickiest parts to figure the true dimension.  You ask me why?  First of all, 4’ is paved and continues on the paving slope, which can change if it is in a super-elevation.  Then, the 4’ remaining is grassed or graveled and is on a negative 8% of slope, unless if it is in a super, then it probably has to ride up holding to a 6% difference with the adjacent paved shoulder (sounds like a guy spinning plates on a stick).  If you add guardrail, it widens another 3’.  It just so happens that the guardrail detail is not in the plans, so you will have to go online to the DOT website and find their detail for the guard rail which may actually add some paving.  If you find more than one guardrail detail, then I suggest you go complain to city hall.

Figure 6 - To view this image CLICK HERE.

When in a cut section a ditch will be added to the left or right side of the highway.  In Figure 6, it shows a 4:1 ditch that is 12’ from the hinge point of the shoulder.  This is relatively straight forward.  However, you really need to go to the station ranges shown for this template and check the plan and profile sheets and the cross-section sheets to be sure that there is not a different profile or alignment for the ditch.  Trust me it happens.  Remember, the word TYPICAL is used in the detail template.

Lastly for the template are the ties to original ground.  If you notice coming out of the ditch at 6’ from the centerline of the ditch there is a break in the slope from 4:1 to 2:1 and this will be continued till it breaks out at existing ground.  In this template at the right side it shows fill condition tie.  Which is a negative 4:1 slope till it intercepts existing ground.  However, you need to step through the cross-sections to be sure that this is not changed due to a deeper fill and the tie slope is made steeper.  They change.

Figure 7 - To view this image CLICK HERE.

The intersection detail looks very straight forward and makes sense.  However, on this project the cross-sections did something completely different.  The reason is at an intersection turning lanes are constructed and the sections held to very different points that made bumps in the main part of the highway.  There was no detail for transitioning from normal section to adding turning lane for the intersection.

Then you still have the typical templates that have curbs on the outside edges of pave and how they transition.  This is all parts of one project.  BE THOROUGH.

The point I am trying to bring up with this entire article is highway modeling is much more intense than just a centerline, profile and template.  It is constantly changing; remember you have several different sets of plans and the standard DOT details that are referenced.

When things don’t make sense, build a rapport with the DOT designers.  Ask what their intent is for the area in question.  In most cases the DOT staff wants to communicate and explain what should be done.  Keep you client the contractor informed on issues as they arise, don’t surprise them.

Till next time.