Here are the very worst interchanges on the major road network of Great Britain. There are 52 in total, each with its own page explaining where it is, what it does, and exactly why it's wrong. You can even respond - if you think a junction hasn't had a fair hearing, you can post your views for others to see.
Junctions can be bad for all sorts of reasons. But in this section, we're looking for bad design, not just the most congested places. Very often the ones most badly affected by congestion are of a perfectly good design, and are just no longer suitable for the amount of traffic they carry. Congestion can also be a symptom of bad design - and that's what we're after.