I dont know if you tuck your laces away if wearing trainers etc but I had a knee injury and had been to the doctor's with it.
On my way out to a busy road my left laces got tangled round my pedal and I couldnt free them.
I was hopping around trying to pull them free and ended up flat on my back with half my body on the main road with a load of cars fast approaching.
I can only say that I moved quick damn sharp back onto the pavement and carried on trying to free my laces with out success.
Eventually some lads stopped and rushed to help and I said my laces were caught. They cut them free and I was able to carry on.
After some City Gent in his pinstriped suit stepped over me and carried on. Mmph.
So if wearing shoes with longish laces, tuck them away!