I'm curious about the advantages of this configuration
? Why the parking lot segment rather than the turn restriction?
Yeah, it IS intentional - both the design and the presence of the parking lot road, and there are definitely advantages to this over the turn restriction. A lot of this comes from experience, and I typically create these on cloverleafs, or 'freeways with off and on slip roads'.
With this bowtie crossover...
* The two parallel roads are so close together, at the 2m zoom, that on a client, it just looks like 'one slip road'. Completely transparent to a client user.
* The only nav advice Waze will ever give a person coming from I-5 N is to take the left ramp of the two, and in the context of this exit, it's 'straight ahead'. (I'll have to show a maps.google.com link to explain, but I've driven it. See http://goo.gl/maps/IFqjs
). The placement of the bowtie is right in front of the actual road split so the TTS shows the right distance. The parking lot road is there to assure that there is not an off-and-on nav suggestion (going back to I-5), but if someone DOES do it, it won't generate a UR either.
* A person coming from S 38th St will get two options, with the correct TTS: either 'stay to the left, to SR-16...', or 'stay to the right, to I-5 N / I-705 N...', thus the careful placing of the fork and the angles.
* If we do this 'the other way' with a single segment and turn restriction: when enough clever drivers do an off-and-on on one of these slip roads, I've seen from experience that inexperienced editors will go to such a junction with a UR, see 'Restricted turn might be allowed', and invariably will allow the turn - meaning 'allow the off and on' - because it's in theory possible, and we're back to an off and on issue again, so it goes in circles.
When I do THIS with a ramp, especially if locked down, this is generally the end of it. Everything works properly, and we don't get turn allow URs, 'incorrect junction' errors because of bad TTS instructions, or circular edits. I did one of these on a cloverleaf on I-405 in August as a testbed, and never saw a UR generated by problems with the bowtie.
(Apologies for how long it took to get back to you all! I hadn't subscribed the topic, so I just plain missed replies after the initial couple.)