# Building Widening Surfaces

Okay, so I’m trying to find the best way to build widening surfaces. These are projects where you have to project out the existing slope for the widening. I have all RPS tools and I know some of them are needed. For sure the offset slope command.

Here’s my biggest pain point though. Usually we can’t trust the engineer’s original ground surface to be accurate to the field conditions created by the contractors actual survey. So, right now, the best method I’ve found is to require the contractor to topo two shots to project the slope of existing, but every 25’. If we do every 50’ our surface is going to have 50’ chords which will not fair well with the machine control. It won’t match in the middle of those 50’ chords. 25’ is much better but also time consuming for the contractor, especially on large roadway projects.

Here is my thought: how can we use the engineer’s existing shots, say every 50’, combined with the vertical geometry of the engineer’s OG surface? Also, how could we make it so they don’t have to topo both spots on the road for the slope. Generally the engineer’s surface is sufficient for the cross slope of the existing road, it’s just the varying of the elevation as you go down the road and they used different control. So, can we easily extract the slopes from the OG surface, then adjust just the lines to the asbuilt survey, maybe just using the RPS “Adjust LS Elevation” command? Combine that with the RPS “Optimize Linestring” command maybe? So there is less data to work with? Engineer OG surfaces often have a lot of detail in them so elevating based on those surfaces creates a lot of VPIs.

I really can’t figure out an efficient way to model widening jobs when it’s all based off existing.

you may be overthinking it. Theoretical DL’s are created just for that reason - Based on a 50’ station grid(industry standard), your quarter stations will hit at a station and offset relative to the design criteria.
While your match line may have some variation along its plane you next feature usually smooths out.
If we are required to match a cut line exactly we will use a sonic tracker on the cut chase but the heel of the grader is going to feather out the transition to design grade. Otherwise we create the design and build based on intent.
Area’s that are abnormal we may verify or add data from field measurements. Match existing curb reveals - we field shoot all of those.

The 50’ chording issue for the machine surface can be corrected in you corridor settings or your surface break-line settings.

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I’m talking about projects with no design, no profile or anything. Just project existing slope out whatever distance. Are we talking the same thing?

If you are good with the existing surface cross slopes draw two lines at offsets to the line of the road that are over the existing surface area - draw them 1’ apart. If the slope of the surface is good enough use change surface elevation to drop them to surface Grade. Now you can use offset Slope off those two lines to project the grade out the distance you need

Does this not solve the issue you have?

What am I missing if not

We are working right now on some major improvements to Adjust Linesteing Elevation command - one allows you to elevate lines to a surface but control where you compute elevations (intervals etc vs at all triangles) currently we are using it to elevate arcs in lines not intervals along straights but that could be added as an option and now woukd be a good time to do this.

Alan