AutoCAD Civil 3D Tip: Help! My Corridor is Slowing Me Down, pt. 1

A sure way to bog down a corridor and enlarge the file size of the drawing is to have too many frequency lines in a corridor. The optimal number of frequency lines in a corridor should be thought of as just enough to accurately define the intended geometry and not one extra line.

Let’s take a look at a corridor. The orange lines are the frequency lines and the magenta & white lines are the feature lines. We can see that it looks like some frequency lines are spaced at a specified interval, while others are all bunched together.

If we zoom in on our frequency lines we can see in one location there are 5 frequency lines inserted into our corridor over a distance of less than a foot. It looks like there is more than one location like this here. This many frequency lines bunched up in one location is very unnecessary and does not add anything of value to our corridor definition. Removing unnecessary frequencies will speed up corridor rebuilds and make the file size significantly smaller.

Let’s note our file size before we go further. The top file contains our corridors and is appx. 17MB.

If you need a refresher on corridor frequency settings, take a quick look here: Frequency to Apply Assemblies Dialog Box

Some people may turn all the frequency options on, thinking the corridor will be more accurate with more lines and being more accurate is good, right? Not necessarily. Let’s zoom out and get the big picture. This corridor geometry is made up of mostly smooth, large radius curves and long tangent sections. We certainly don’t need our model to communicate 5 frequency lines in a one foot length of corridor to our contractor. He’s not going to stake the road out using a ruler.

So, what settings contribute to adding the most extra frequency lines? Let’s check the settings in our Frequency to Apply Assemblies Dialog Box. Specifically, the settings that effect frequency in curves. Setting the frequency for Along curves and Along offset target curves to “By curvature” and also having a very small” Mid-ordinate distance to define curvature” value will fill the corridor with many more frequency lines than are necessary. This combination of settings can create a ridiculous amount of extra frequency lines.

0.100’ is a very small interval, let’s up the Mid-ordinate distance from 0.100’ to 2.000’

Let’s rebuild and take a look.


The bunched up frequency lines are gone. I’m happy with this corridor showing only 25’ increments at this point. Remember, specific stations can be added manually if the definition requires it. Let’s look at the file size now.

Our file size has gone from 17MB to 11MB and we haven’t lost any significant data needed to construct this road. Let’s go one step further, and set Along curves to “At an increment”, and Along offset target curves to “<none>”.

Let’s check the file size again. It is now even smaller, from 11MB down to 9MB.

Even in this small file I can enjoy tangible gains from changing the curve settings. The corridor builds faster and the file takes less time to open. An even larger file would see even more gains.

Bryan Sullivan

Bryan Sullivan

Bryan joined the EnvisionCAD team in October 2013. He provides a variety of CAD Management services. As a CAD Technician, he provides expertise in AutoCAD and Civil 3D production, support and development services. He has been using AutoCAD and Autodesk products since 1998 and has used his knowledge of CAD software and internet technology to provide drafting and design support and CAD management services for engineering firms and design-build contractors. Bryan has training in mechanical design and has gained experience in the civil, environmental, and structural engineering fields while working on a variety of projects for state, municipal, and private clients. His project history includes 2D and 3D CAD modeling of waterworks and wastewater systems, transportation systems, floodplain and stormwater management design, landfill design and operation, earth retention design, deep foundation systems and much more. He is skilled in creating plans and documentation for the entire engineering process as it evolves from the initial survey and design, on to the permit process, through the creation of engineering plan sets, cycling through changes made during bid preparation and review, and finally ending with construction and as-built drawings. He is an avid researcher and has never been reluctant to leverage a new technology or evaluate a new solution in order to solve an engineering or production issue.

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