The dumbbell is a hybrid between the diamond and the roundabout interchange, which makes it a very close relative of both, since one is a direct descendant of the other. In short, it combines the capacity benefits of a roundabout interchange with the smaller footprint and single bridge of a diamond junction.
Where to Spot Them
Look on newer roads and those that have been remodelled recently.
- Cheaper than a roundabout interchange, with just one bridge and less land take.
- An easy-to-build step up from the diamond junction.
- Lower capacity than the roundabout interchange, with two roundabouts working less skilfully than one.
- Often installed today where a larger roundabout interchange would have been built before.
Most variations can be accounted for by the installation of a roundabout on only one side of a diamond junction. There are numerous unique layouts that involve two or more roundabouts and which are best described as dumbbell derivatives. You can also flip the sliproads round to the same side of the roundabout and create a folded dumbbell.