Multiple Alternate Surfaces

I would say 'No' if you are strictly refereeing to the Alternate Surface option within a template.  If you assign an alternate surface to a point that is also part of the Top Terrain, then it can be in two different surfaces terrain models.

There is also an ability to create terrain models from elements.  This can be used to assign features from a corridor to multiple terrain models.  These terrain models from elements will follow along as the corridor template is modified.  So, in that way it seems to have the ability for any one point or feature in a corridor to be part of as many Terrain Models as you may need.  Not sure if that helps but it may be useful in some instances.

Hi Mike, I was indeed referring to the Alternate Surface option within the template. I am familiar with the more conventional methods of creating different surfaces but was wanting to play around with optimising that within the template. Example to create 2 alternate surfaces where one is for top of pavement only (for aquaplaning checks) and the other a complete design surface. Seems like using graphical filters or terrain from elements remains the preferred method.

Use an end condition instead of that project to surface constraint.  You can then use target alias to seek multiple surfaces. 

You are probably aware of this, but you don't need to specify the complete design surface in the template. Depending on the design stage settings, the top-surface is created for every corridor even when no alternate surfaces are specified. To my knowledge alternate surfaces are only needed when you need an alternative to this default top-surface.

EDIT: As Shawn pointed out below, the top-surface (exact name: Top mesh) that is created is not a true terrain model. Some tools recognise it as a surface that can be used in the same way as a terrain model, e.g. Sight Visibility or the profile creation tools. Other tools such as Aquaplaning apparently require a true terrain model.

You are probably aware of this, but you don't need to specify the complete design surface in the template. Depending on the design stage settings, the top-surface is created for every corridor even when no alternate surfaces are specified. To my knowledge alternate surfaces are only needed when you need an alternative to this default top-surface.

EDIT: As Shawn pointed out below, the top-surface (exact name: Top mesh) that is created is not a true terrain model. Some tools recognise it as a surface that can be used in the same way as a terrain model, e.g. Sight Visibility or the profile creation tools. Other tools such as Aquaplaning apparently require a true terrain model.

Correct, requires one addition step to create the terrain from Design Mesh... The Terrains from Meshes tool can set specific Feature Definitions for the proposed terrain (e.g. boundary, void and surface) and  "side of closed mesh".   Top and Bottom can be done, however the Terrain Filter and alternate surfaces methods provide more control for pav only and subgrade terrain development.  Another possible benefit to the Terrain Filter method is how it remains dynamic to the 3D linear feature changes produced by corridor updates. 

Terrains from Meshes produced using this tool do not seem to remain dynamic to the corridor mesh changes, despite the mention of "ruled" options in the tool settings dialog.  This suggests you'll need to use the tool again to reproduce the terrain each time the corridor design changes.