5, 6 and 7 ramp parclos

[jackal]

Latest replies to Peter:

1. Roundabout bias?
My position is "pointing the traffic in the direction it's going" centric rather than roundabout centric. At a stackabout or stackamond, traffic is moving in a basically circular motion, so it makes sense to build the road to a basically circular form. But where traffic is moving in other ways, other forms will be appropriate. For instance, SPUIs and DDIs have traffic islands to send traffic in the desired directions. See also this signalised junction we've discussed in Copenhagen: https://www.google.co.uk/maps/@55.63798 ... a=!3m1!1e3

I'm sure you're not really saying that we should discard the user friendly designs in these cases and build everything as 90 degree turns. So I don't understand why you apparently think that is preferable for a stackabout/stackamond.

Look at it this way: you only have 360 degrees to play with, so why give as much of that to an illegal turn as to the legal turn (i.e., 90 degrees left and 90 degrees right) as a stackamond does? A roundabout corrects that by giving the illegal turns acute angles every time they occur, opening up gentler angles for legal movements.

2. Is a stackamond a diamond?
It's an interesting thought that a stackamond is a squared off diamond (with the extra level of course). I don't think it functions like a diamond though. For instance, the two surface street straight-over movements at a diamond get greens simultaneously, which the equivalent movements don't at a stackamond, due to the far greater space between the carriageways (or "carriageways").

But as a hypothetical, if you had a diamond that had enough space between the carriageways of the surface street, it would be better off as a signalised rbt, for the reasons given already. Again, I can't see what reason you can really have (aside from future proofing and maybe familiarity) for not wanting a junction to curve in the direction of travel where there's the space for it. It's a pretty fundamental aspect of road design that you don't try to "catch out" the user with unnecessarily sharp turns where there's the space for gentle ones.