Alan Sharp

Advanced Corridor Modeling

Blog Post created by Alan Sharp on Nov 3, 2018

As I spend more time with Dealers and Customers, I have found that there are many things in Corridor Modeling that are either unknown or mis-understood. Over the next few weeks  am going to post some blog entries here that address a number of things that I commonly encounter


In the enclosed video - I cover the concept of Composite Modeling - what is that? 


Many people that I meet believe that Site Modeling (Data Prep) and Corridor Modeling (Roads) are two completely separate disciplines. This is a mis-conception. In order to build many roads and their associated features, you cannot compute everything perpendicular to the center line - examples of this would include the following


  1. Bus Lanes or Lay Bys / Turnouts. While the pavement of the turnout may be at the slope of the pavement computed perpendicular to the centerline, the shape of the turnout is such that if there are features such as curb or sidewalk etc elements that follow the edge of pavement and require true cross slopes - you have to model those elements at least through the bus lane perpendicular to the edge of pavement / lip of gutter feature node.
  2. Bulge corners on subdivision roads - again same as above, the bulge corners deviate from the centerline, so all subsequent feature lines for Flow Line, Curb Face, Back of Curb and Sidewalk need to again be modeled separately
  3. Cycleways - many cycleways may parallel a highway in places, but then deviate away from the highway centerline - that means they either have to be modeled as a separate corridor or that they get modeled using Site Modeling methods and then get added back to the overall model for the project.


Each of these scenarios requires the "composite modeling" approach that is demonstrated in the enclosed video, and this approach delivers a lot of flexibility and great results.


When modeling corridors - look at the drawings closely and identify areas that will require the "composite approach".


In the example shown in the video, you will also see the use of Tables in Template instructions (Both Corridor and Sideslope Templates), and how you can use those to start and stop elements of a Template - this is a second thing that I have found over the last year that is pretty much an unknown feature of corridor template instructions that is one of the most powerful features of templates - and that is the use of ? in an Offset or Elevation Table that states that from this station forwards the Offset or Slope is "Unknown" or "Undefined" and acts as a Stop to the feature being created by the instruction i.e. a set of Station / Offset values such as these below


Station = 0          Offset = 12

Station = 50        Offset = 12

Station = 100      Offset = 24

Station = 200      Offset = ?

Station = 300      Offset = 24

Station = 400      Offset = 24

Station = 450      Offset = 0

Station = 450.01 Offset = ?


will create a Gap between stations 200 and 300 and will stop the feature at Station 450.01


What is more, I also find that many users do not understand the difference and benefit of selecting Previous Node or Specified node as the reference line for a new instruction


  1. When you select a "Specific Node" - the instruction being completed can only be created if the Specified Node exists - so when you use tables that use a ? to stop the reference feature over a station range from being created, then if you select that stopped reference line as the reference node, then the instruction will also stop over the same station range without having to define any tables on the instruction. The same applies to subsequent instructions, if they are dependent on a prior instruction - then they too will stop in the same gap areas. This is a great way to create "feature sequences" that meet the need of changing Typical Sections along the highway.
  2. When you select "Previous Node" then the instruction will always be created and will use whatever the last node that was created in the instruction list prior to the instruction being created. If you want the new feature to "skip" a range of stations, then you can use a Table containing the ? at a specified station and it will cause a gap in the instruction for the defined station range. For example if you have a Pavement section of 12' at -2% for the full highway, and then you have a Taper that starts at station 50 (as per the above table), then stops at Station 450.01 (as per the above table), but you want a shoulder that runs along the Edge of pavement from 0 to 50 and from 450.01 to the end of the road and along the Taper from station 50 to 450.01 but with a gap for a T Intersection from Station 200 to 300 then using Previous will do the trick because the previous node will be EOP first and then TAPER and then EOP over those station ranges - if you did not but a Table with the gap between 200 and 300 stations, then the shoulder would step in and be parallel to the EOP through the gap section (which would be undesired).


So combining all of the above, allows you to skip areas that you will later fill in with site modeling techniques that will then get added back into the corridor as 3D Reference Lines and then Connect instructions to join the strings into the corridor model, or added to the corridor surface model as additional breaklines using Add and Remove Surface Members.


The video below shows all of these things. In my experience, when you master these "tricks", you will be a far better and faster modeler of road projects



Hope this is useful

Even Happier Modeling .....