Undertaking = passing on the left, in a system where traffic is meant to drive on the left and pass on the right. By analogy with overtaking, for passing on the right.
Cyclists (in a bike lane or not) undertaking heavier vehicles certainly are involved in a lot of serious accidents. However it's a very twisted view of reality to say that this causes accidents. The proximate cause is the heavy vehicles turning left or pulling to the left without regard for the cyclist in their blind spot.
Oh that's a nice word! Being alive is better than being right, so blind spots are a bad place to be. Actually it's fine to be right behind a big vehicle, but I never want to be beside them for more than a couple of seconds...
Cyclists (in a bike lane or not) undertaking heavier vehicles certainly are involved in a lot of serious accidents. However it's a very twisted view of reality to say that this causes accidents. The proximate cause is the heavy vehicles turning left or pulling to the left without regard for the cyclist in their blind spot.