Diamond Interchange
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The most basic way to connect a road to a motorway or motorway-style road is a Diamond interchange. It's quick, it's cheap, it's easy to build and use, and it demands very little land. One bridge over the top and four directional sliproads, as simple as that. Their downfall is their low capacity, and this explains why we don't have very many in this country. They are important, though, because most other motorway-to-road junctions are derived from this simple design.
Where to spot them
Usually found on old motorways, connecting to fairly minor crossing roads.
- M1/A5120
- M6/A534
- A14/A5199
Advantages
- Low construction costs, with just one bridge and very little land-take.
- Easy to upgrade later - stick some traffic lights at the top of the sliproads, for example.
Disadvantages
- Low capacity - there's lots of conflicting traffic at the end of the sliproads.
- Hard to substantially upgrade to, for example, a roundabout interchange.
Variations
The simplest variations take away a few sliproads to make it limited access - leaving half-diamonds.
You can start looping round sliproads as well, which takes up more land, and turns the whole thing into a folded diamond (or sometimes, a half-folded diamond). These are sometimes also known as partial cloverleafs (or parclos) as they're halfway to being a cloverleaf.
Finally, it's possible to add roundabouts into the equation, but if we do that we're into other interchanges entirely...
