Pithecanthropus wrote: TOS wrote: sean wrote: 
Road planners need to stop smoking crack.
that's the hot new thing
Diamond interchanges actually make a lot of sense, and they're not at all confusing to drive on. It might look weird from the air, but on the ground it's easy.
I'm thinking this through further...
It looks like this replaces a traditional flyover ramp design. It looks like it might take up a little more space, but not much, and it looks a lot simpler to engineer and build. I doubt the confusion lasts more than a couple of drives, because it is signal controlled at the intersection.
Issues I see include the long intersection distance from where you stop to where you are clear, and the presence of the left hand merge, something not super common in standard onramp and offramp designs, that people need to get ready for. It also seems like a short merge when jining the main road from the left, particularly if you then need to get over the the right to avoid returning to the freeway, but I guess that road isn't running at freeway speeds either.
Reconsidering what I said about collision points, while it does not reduce the number of traffic lights relative to standard flyovers, it would make them 2-direction intersections, with no left turn phases needed, which should simplify intersections and speed up flow and clearance. That also should reduce collision points, though a traffic circle at that cross would potentially be even better in that respect. Plus, a traffic circle would reduce concerns about an inattentive drive (especially one who is tired or impaired) getting it wrong, by preventing a straight-isa drive through path that leads to the wrong direction.
On the other hand, I've certainly seen elaborate flyover designs that do not need a traffic light at all, but they are complex and expensive, and often there's another intersection so close they aren't a big help. Also, it doesn't look like this would work well on smaller roads, though maybe it would be over-engineering on a 2-lane road anyway (where it seems like it'd work, but awkwardly). It's definitely over-engineering on a 1 lane road.
My big question would be how does it handle traffic? It seems like it could backup badly, in a way even worse than flyovers would, but maybe the improve intersection design (just 2 directions with no turns) makes that less of an issue. But if entering traffic is backed up badly (or if you are running metering lights and backups get really bad) it looks like it would be an extra-big mess.
I've also assumed this is a major city road intersection a major freeway. If this is a less major freeway or a highway intersecting a freeway, that brings up other possible concerns (like higher speed on the merge, the impact of higher speeds on people mishandling the crossover intersection, and the undesirability of traffic lights on a highway).
