In my previous article, I began my multi-article discussion regarding proposed grade contours. As I mentioned in that article, proposed grade contours are almost universal for every project.

Your projects are more likely to contain this grading information than any other and the engineer will likely provide proposed grade contours with each project. However, proposed grade contours are not the most accurate source and should be used with. In my practice, the worst example of bad data came from data was build solely from the engineer’s proposed grade contours. This practice is not only dishonest to your client, but will cause multiple and significant grade errors in the field. This topic warrants multiple articles discussing the proper use of the engineer’s proposed grade contours when building data.

Over the years I have worked on a large variety of projects. I break them down into one of three types: roadway, site and subdivision. While there are exceptions, these categories distinguish how a project will be built and the type of grade information I can expect from the engineer. For this article, let us explore the proper use of contours for roadways.

My definition of a roadway is any portion of a project that has plan and profile information provided. This can range from a simple hundred foot access road to miles of multilane heavy highway. Sometimes it is an actual road, and other times it could be just a bike path or a special section of dirt grading. Regardless, when building data for a roadway type project your primary source of grade information is going to come from the information contained in the engineer’s paper plans. Roadways are special because they are the only type of project that can be accurately recreated without any type of electronic files from the engineer.

A good set of roadway plans from the engineer will contain grading information from plan, profile, typical sections, cross sections, super elevation transitions, intersection details, and any other specific grading and layout information. By definition, this information is precise for both location and elevation. As long as the engineer has correctly designed the roadway, and presented this information clearly and correctly, this is the one and only project type where you as the data builder can recreate the project accurately. This is because the above sources of information allow you to mathematically know the exact elevation at any given location along the roadway. Recreating roadways as a data builder takes both skill and patience. In my experience they are the most difficult and time consuming projects.

So how do proposed grade contours fit into this complex design? They do not.

Let me explain. Unless the engineer failed to provide detailed grade and/or layout information for some aspect of the project, I never incorporate proposed grade contours into my roadway projects. They simply do not provide enough detail. As an engineer, it is much more accurate to detail the roadway out in other ways. For any given roadway project, I recreate the roadway using the paper plans. Then if the contours are available, I will use them to double check my work. They are not included in the final product in anyway. This is because proposed grade contours, no matter the interval, cannot accurately show vertical curves, super elevation transitions, intersection grading, roundabout grading, gore points and every other grading feature that doesn’t happen to magically coincide with the contour interval.

The exception to this is that engineers will commonly use proposed grade contours to detail out areas of earthwork outside the roadway. Grade features such as ditches, inconsistent daylight slopes, driveways and other areas of unique grading outside of the roadway can sometimes have no specific grade information in the plans, outside of proposed contours. Obviously if proposed grade contours are all you have for that area, then that’s what you have to use. Even when this is the case, it will usually represent a very small and isolated portion of the project.

But as a rule of thumb, roadway projects should use proposed grade contours as the last source of information. At the end of the day, if your roadway data project does not use proposed grade contours, you have likely built the 3D data correctly.