As an alternative to the cloverleaf, site a roundabout as an extra top layer to the overpass, joined to/from the innermost lanes of both roads in both directions.

Turning vehicles store energy altitudinally while joining up with the roundabout, likewise accelerating while rolling down the merge ramp.

In order to keep from having to drastically grade the immediate locale, the slower road is the overpass (middle layer).
-- FlyingToaster, Sep 24 2012

as prodded by [bigsleep] in a Steam_20catapult_20for_20highway_20merges
annotation. [FlyingToaster, Sep 24 2012]

I could have sworn we'd done this one for intersections, but I can't find it right now.
-- MechE, Sep 24 2012


*an
-- Voice, Sep 24 2012


yep, I posted a few years ago, deleted it 'cuz it was too practical, reposting 'cuz I was going to, and [bs] reminded me of it.

**a
-- FlyingToaster, Sep 24 2012


Multi-level junctions are Baked and Widely Known To Exist ...
-- 8th of 7, Sep 24 2012


Worcester Massachusetts is lousy with multiple-exit cloverleaf ramps (not to mention exit-only ramps, left exits, center-lane exits, and every other maddening Hot Wheels stunt track variation the road planners could devise). At least one of them is a three-level spiral with seven or eight offshoots.
-- Alterother, Sep 24 2012


[8th of 7] cite for a sky roundabout ? or are you just blowing wind out your respiratory venturi.
-- FlyingToaster, Sep 24 2012


The notorious intersection at Hospitalet de LLlobregat on the South-western side of Barcelona, where the spur to the airport connects.

M57/A5300 junction at Huyton.

Escheresque collision of two autoroutes and several local roads just North-east of Calais. The approach to the Eurotunnel/Cite d'Europe complex has a similar nightmarish quality.
-- 8th of 7, Sep 25 2012


//        M57/A5300 junction at Huyton.   //

I spent a week there one afternoon.
-- Alterother, Sep 25 2012


Ah yes, the Tarbock exchange. If I was to call that anything printable, it'd be "ring road". Got a couple of those out this way: 3rd or 4th time around you get used to it if you aren't too dizzy.

If you remove all the other roads from there except the two highways, and put a small roundabout as a 3rd level to the over/underpass, and route the inner lanes (existing or diverging from existing inner lanes) up to the little roundabout, and put a small statue of somebody looking a bit constipated in the middle, that's what I mean.
-- FlyingToaster, Sep 25 2012


A big statue of someone looking very constipated would have more dramatic impact, shirley?
-- 8th of 7, Sep 25 2012


In what way does this differ from almost every major road and motorway junction at present?

The roundabout is elevated above the larger of the two roads; traffic on the larger road passes uninterrupted beneath the roundabout; traffic on the lesser road rises to the roundabout; traffic exiting or entering the major road leaves or enters via the slip roads. Or have I misunderhended?
-- MaxwellBuchanan, Sep 25 2012


Where two major highways of equal size, designed to maximise continuous flow,cross, the intersection takes place on two levels, as one set of carriageways passes over another, the transitions being accomodated by" off" and" on" ramps.

The disadvantage of this is there is no second chance; having selected the route from the (say) Eastbound carriage way of one highway to the Southbound carriageway of another, the driver is obliged to proceed South until the next junction.

With a third level roundabout in the system, traffic leaving the highway can subsequently elect to exit back on to any carriageway, including reversing direction.
-- 8th of 7, Sep 25 2012


For clarification, it's just the turning traffic that goes all the way up to the roundabout. The rest of the traffic just goes right on through the over/underpass as usual.

As well as the convenience of being able to turn backwards, go in either direction or change your mind and continue on the same route, without any navigational gymnastics, a bit of forethought into grading and the whole thing is energy regenerative as well.

The place to put a rest stop and a map too.
-- FlyingToaster, Sep 25 2012



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