Got to be a multitude of reasons, anyone driving in and out of town will see the state of driving is poor - I had a car full of a certain race the other day slam on her breaks outside the m.e.n and sat there giggling with her friends at the abuse she got from my car window (possible insurance pay out attempt i.m.o), you drive down parkway in the morning and everyone cutting in last second, come off at motorway junctions and your Audi drivers going from 3rd lane to exit in one sweep, poor road markings and visitors to the city making last second decisions to change lanes, a lack of mobile police to enforce driving standards instead of a cash cow van sat there picking up speeders, the standard of the roads is poor, more so out of the city centre but cyclists taking their lives in their own hands avoiding pot holes - i hit one about two years ago in my car and it smashed the wheel up n blew the tyre out, not only did i have to fight for a year to get the damage paid for but the attitude of Salford council was appalling, if i had been a cyclist I would have undoubtedly been thrown from my bike - far as this 20 is plenty thing, do me a favour, we may as well just walk everywhere and anyone doing 50 as was mentioned elsewhere shouldn't be on the roads in the first place - they wont honour a 20 zone if they wont honour a 30