I have some knowledge about the stretch of road mentioned by Bruce Schneier. I still know a good number of people who use that stretch of the M4 regularly. In the main, rather unsurprisingly, these speed cameras aren't welcome. Mainly I suspect because people enjoy speeding and feel a bit put out that they are being asked to control their speed or pay the penalty of a fine and points. I understand that the police are trying to convince motorists that speeding is an anti-social activity in the same vein as drink driving. In terms of the campaigns there are some parallels between the two, I've heard the following arguments from both "anti-campaigns" in the past:
Drink / speed driving actually makes you more aware because you are high on adrenaline.
Drink / speed driving in the early hours of the morning is perfectly safe because there are no others on the road at that time.
Anyway the stretch of the M4 approximately lies between Swindon and Bristol. I made that journey pretty much every working day for about 2 years, in that time I saw many accidents, and far too many road works. On average I'd say that the 50 mile trip to work would take about 65 minutes. If there were roadworks or an accident then this time would exceed 90 minutes.
Curiously, the best travel times I had were during the fuel protests where the average speed on the motorway was set lower which also carried the bonus of reducing my fuel bill.