Partially Unrolled Cloverleaf
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The main problem with the cloverleaf interchange is that it causes conflicts between traffic entering and exiting the motorway on the sections between loop ramps. It's also very big. While this interchange probably isn't any smaller a normal cloverleaf, it manages to remove the conflict by unrolling two of the loop ramps onto the outside of the junction.
Advantages
- No conflicting movements between entering and exiting traffic.
- Unrolled right turns are faster as a result of the wider curves.
- Can be used where minimal land is available in one corner of the junction: one corner only has a small left turn slip road to fit in.
- It's only on two levels - the M25/M40 junction uses this design and is entirely in cutting below ground level to minimise its impact.
Disadvantages
- Large land take. One example has three or four large fields just in the space behind the exit in the bottom left of the diagram above.
- The pair of sliproads that loop around the outside form a dual carriageway where traffic is on the "wrong" side of the road. This is actually very scary, particularly at night where headlights approach on the wrong side!
- Excessively long name.
Variations
There aren't many variations on this theme. It's essentially a variation on a cloverleaf itself. The exception is the interchange between the A19 and A66 between Middlesbrough and Stockton on Tees, which is mostly a Partially Unrolled Cloverleaf, but replaces one of the loops with another direct sliproad.
Where to Spot Them
- M6/M62
- M4/A329(M)
- M25/M40
With thanks to Stuart and Ian Bailey for information on this page.
