→Limited Access Interchanges
== Limited Access Interchanges ==
When two roads meet in a limited access interchange (any situation where travel between
the roads is facilitated by ramps alone), extra care must be taken.
If an exit ramp lines up with an entrance ramp, care must be taken to restrict the straight through direction to prevent "ramp-to-ramp routing" where the routing engine may try to take a shortcut from the Freeway, to the exit ramp, to the entrance ramp, and back to the Freeway instead of staying on the Freeway. That motion is inefficient and may be illegal in certain jurisdictions.
=== Diamond Interchange ===
In the simplest form, this can be represented as single connections from the ramps to the surface street. Just be sure to restrict the straight through motion from the exit ramp onto the entrance ramp.
=== Single Point Urban Interchange (SPUI) ===
A SPUI is a very space and flow efficient design, but it takes extra attention to ensure the turns are correct. And as the name indicates, ideally there should be a single junction in the center. You may need to tweak the geometry of segments a bit off of alignment from the real physical world, but it should be minor if the interchange is a true SPUI.