538 is not a half diamond. It's a Texas frontage road setup.
In TX, slip ramps leave the mainline and intersect parallel frontage roads. Along these frontage roads, there's local access & local roads (sometimes with access to the other side of the freeway, sometimes not), sometimes more ramps (onramps or offramps, in whatever order), sometimes not.
Sometimes, there's only one intersecting road, sometimes more than one, sometimes none. Whether there's a grade separation or not.
Partial interchanges of every shape and configuration are common, as are adjacent interchanges' footprints overlapping.
Point placement can be easy & obvious if there's one offramp & onramp on each side of a single grade-separated crossing. But very often, this is not the case.
With all this going on, the straightforward practices of how to handle more garden-variety interchanges start to break down. Things become more of a judgment call.
The most salient part of the manual link was the bit about "Use your best judgment."
538 is placed at the southernmost intersection before the frontage road merges back into the mainline, and that's sufficient.
545: Within footprint of 546. 1PPI.
It's really not. This is one of those Texas things
It really
is. Precisely
because this is one of those Texas things.
where the ramp exits to the frontage road a mile before the actual interchange.
The ramps
are the interchange. They connect to the frontage roads, and any other intersections downstream/upstream are incidental. There's no corresponding west-"pointing" half to center us around any particular location.
Be careful not to conflate "interchange" with "grade separation". These are
different things, and one does not mean the other.
584 added.
