How do template transitions work

I see a number of questions relating to corridors “not doing what they should” and many of those issues tie back to the way that Templates transition between each other. I am not a huge fan of using multiple templates to build corridors, I try to build my corridors with a single template and use Tables and lines to transition widths and slopes etc. I also try to create a master list of nodes that need to be built to cover all of the needs of the corridor, and then try to build one instruction for each node in the “overall cross section”. This way it is easier to track what is happening.

Having said that, it is clear that many users, especially those that used Terramodel in previous lives, want to still do Templates the same way as they used to. In that case then you really need to understand how they transition.

The main challenge with Templates is that each template inevitably defines a different type of section based on “typicals” provided in the plans. One way you can stop transitions from happening is to create a reference template at the end of the station range for the “typical” that references to the template that is placed at the start of the station range. This way the template cannot transition. Then the next template that has a new section definition is placed 1mm or 0.01 feet up from the reference template so that any transitions happen over the 1mm distance and will not be noticeable, however be aware that some things may step in offset or slope or elevation because they cannot transition over a distance.

Next option in templates if you want to stop them transitioning, is to use Tables for all instructions. Tables take control 100% of the element over the entire station range of the template. so you can create an Offset Table or a Slope Table etc. and only need to enter 1 row in the table - the start station and the start offset or slope and the elements will not transition as a result. If you then want to transition the widths or slopes, you can enter the station at which you want the transitions to start or end and the value at that location for the offset, slope or elevation and you have 100% control over what the element is doing.

Next option in templates is to use the 2D line or a table with 2D lines in them to control the offsets or use a shareable slope table to control the slope. When you do this, those act the same way as tables and take ownership 100% for how the element is computed.

But if you don’t do any of the above then you are down to how templates transition for offsets and slopes. In this case, the template transitions are there to try and work out what you intended to happen between template 1 and template 2. Bear in mind Template 1 and 2 may have completely different elements, element widths, elements slopes and node elevations. The software has to try to work out how to link Template 1 to Template 2 and that is always going to be a guess, unless you help it in some way. The following notes hopefully give you a guide to help you figure it out

  • Currently template transitions do not use the names of nodes in one template and link those to the same nodes in the next template. I have put in a request that node names should be observed as the first thing that guides a template transition.
  • In the corridor instructions, depending on the type of instruction and the configuration of the instruction, there is a setting named "Type of code above" and the options are Undefined, Lane Edge or Shoulder. The transition process groups instructions based on the setting value applied to each element. Note, the terminology is a little misleading, it was initially developed for the Intersection design capability, to help TBC understand how to map pavement and shoulders / other elements in a mainline corridor int a side corridor at a T or X or Roundabout type intersection. It was then picked up as a part of the corridor model to help in Template Transitions. Basically items tagged as Lane Edge are grouped in one template and the next template, and the software tries to map Lane Edge to Lane Edge. If there are more than one lane edge and the number of lane edges match from one template to the next, then they will be matched Lane Edge 1 to Lane Edge 1 and so on. If the number of elements tagged Lane Edge do not match, then the software

The video below explains the offset transitions in some detail, slope transitions work in the same way.