Taking each paragraph in turn:Peter Freeman wrote: ↑Sun Apr 17, 2022 12:54 ^ I've always been amazed by this curious fact too. I don't think it's deliberate avoidance. Rather it's just the way it has worked out.
This tangled mess in Brisbane perhaps counts - the M3 Inner City Bypass (ICB) crosses the M7, which simultaneously splits into the M7 airport tunnel and A3 surface. Here (but better viewed on GE) -
https://www.google.com.au/maps/@-27.444 ... 658,16.11z
Also in Brisbane: follow the Logan Motorway eastwards to its merge with M1. That will become a 4-way when the Coomera Connector Motorway continues the M6 (or M2?) southwards to the Gold Coast. The D3 CCM will run parallel to the M1, which is already bursting its D4 and D5.
A place where Melbourne could have used a 4-way is M1/M3. Now there's insufficient space. There would be M3 northbound to M1 eastbound traffic demand and the reverse if provision was there. Currently there are adequate non-freeway alternatives, and a freeway-based alternative route will eventually arise from planned upgrades SE of there.
Melbourne tentatively plans for three interchanges on its Outer Ring to be stacks, but that project is far in the future. A 4-way is planned at M3/Dandenong-Bypass, when the latter receives its upgrade to motorway. Perhaps a cloverstack. Timing: probably far off.
I'm trying to think of the other extant one you mention. What's an 'offside stack'?
The M1/M3 one is the main example where it almost looks deliberate (more on this below).
I can't see ICB east to M7 north. Like M1/M3, this is one of several cases in Australia where 6 or 7 out of 8 freeflow turns are provided (with only one of the right turns missing). Some others are M2/M80 (Melbourne), Glenloch Interchange (Canberra), and the new M2/A9 interchange (Adelaide). The only 'three quarter access' freeflow interchange like this in the UK I can think of is A739/A814 in Glasgow, which is a bit of a cheat as it relies on weaving and a U-turn (M60/A34 is nearly there but some of the turns are actually to/from M56 only). To an extent one might say that in Aus these are filling the role usually performed by four-way full access interchanges.
I guess the four way M1/M6 would be another example of three quarter access, as there'd be little point putting links between the M1 south and M6 south.
It would not have cost a lot to put in a loop for M3 south to M1 east and the corresponding left turn. I suppose it was built long enough ago that the demand wasn't obvious.
At least the futureproofing is there for this one.
An offside stack has at least one merge or diverge to/from the offside (right in UK/Aus), while having a generally stack-like arrangement (i.e., no loops, the carriageways don't cross over like a gothic interchange, nor are both carriageways splayed to facilitate long turns, i.e., right in UK/Aus). This still encompasses a wide range of designs. The only such interchange in Western Europe is this outside Zurich: https://www.google.com.au/maps/@47.4119 ... 275,16.72z They are more common in the US. Here are a couple of examples in Connecticut: https://www.google.com.au/maps/@41.3007 ... 111,16.31z and https://www.google.com.au/maps/@41.7823 ... 697,14.63z (Obviously, because they have offside turns, they are never going to be completely stack-like, but there is a resemblance, especially with the use of direct connectors for long turns.)
Hadn't noticed that - yes, technically not freeflow, like the full stack in Athens with toll booths. Seems silly to go to all that effort and then signalise it for the sake of a local exit. This is what C/D roads and braiding are for (even more effort, I know). And yes, that issue aside, it's an offside cloverstack in my accounting.Peter Freeman wrote: ↑Sun Apr 17, 2022 14:22Jackal, did you notice, on the Brisbane cloverstack -jackal wrote: ↑Sun Apr 17, 2022 11:05 Anyway, this quirk is gradually being eroded, with the latest additions being cloverstacks outside Brisbane and Perth:
https://www.google.com.au/maps/@-27.645 ... 429746,16z
https://www.google.com.au/maps/@-31.863 ... 210302,16z
(a) The metering signals on a connector and a mainline? It solves the problem of only 400m spacing between an entry and exit, southbound.
(b) The RHS exit in the stack, southbound?
BTW, this interchange has been an almost complete cloverleaf (but with one signalised movement) since 2003. You're right though that it has only recently become full freeflow (not counting the metering .... ).