Underground markings

[DJ-DJL]

Which area of IMT is your request about? (ex: Lines, Fillers, UI)

All

Describe your idea clearly and concisely.

Allow underground markings.
Other tools provide this by means of holding shift, or pressing pagedown first.

Screenshots?

Not applicable

Why would this idea be a good addition to IMT?

Apart from the getting lovely underground junctions, we could potentially use this to create a tunnel where assests do not do this.
Using the props mode to render walls, floor roof etc, we could get a crude approximation of a rendered tunnel on any road.