Three-Level Stacked Roundabout Interchange

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Three-Level Stacked Roundabout interchange

Cheaper than a row of run-down terraces in the path of a planned motorway, and about as cheerful, the stacked roundabout is the blight of four-way junctions everywhere. Everything about it screams "we spent money elsewhere", and there are only a notable few locations where these things can actually handle the traffic flows. They work best where a motorway crosses a fairly important A-road, but whoever first placed one to connect two motorways needs a good slap. They are, of course, the bigger brother of the standard Roundabout Interchange - basically both directions get a flyover. The contrast between the success of the two types is marked.

Where to spot them

Look for the traffic jams.

  • M1/M62
  • M1/A52
  • M60/M62/M66
  • A1(M)/M18
  • M25/A3
  • M6/M65
  • M61/M65

Advantages

Disadvantages

Variations

Most variations that are found on this type of junction are through efforts to increase the capacity of the damned things.

The usual start point is to add traffic lights at every entry point. If (when) this fails to halt the problem, the usual strategy is to add left-turn lanes bypassing the roundabout, and in desperate cases, widen the circulatory carriageway (expensive because of bridge widenings). Simster Interchange's roundabout has reached six lanes now, which is double the width of any carriageway passing through.

A few desperate cases require more action. Lofthouse Interchange has had new sliproads tunneled underneath it at great expense; the A2/M25 junction will be having new elevated sliproads in two directions added in the near future.

The most exciting variant is at Great Barr, which is just mad.