Almost every side road in Watford could be given a 20mph speed limit, if a new study is to be believed.

A study carried out by consultancy firm Mott MacDonald and paid for by 20's Plenty Watford found that 350 out of 380 streets that currently have a 30mph limit could have it cut to 20mph.

It's not a cheering thought, at least for the majority of motorists.

More bumping up and down 'speed cushions', wearing out your tyres and your suspension, not to mention your clutch as you lurch back and forward between second and third.

As with HS2, it looks like the sort of thing that is going to happen irrespective of whether anybody really wants it.

And the only people who look certain to benefit are those in the speed hump business and the car repair business.

So why do it? For a start, nobody actually drives at 20mph through them. Most people drift above it until they get to those 'traffic calming measures' and then slow down to limit the impact.

It is not certain that reducing the speed limit actually does reduce the number of accidents. While a study in Bristol claimed to have saved some lives, a study in Manchester found a drop in the number of accidents in 20mph zones was not as great as it was on some faster roads.

That said, it may be that people are more likely to survive, as the accidents that do happen take place at a lower speed.

And if the thought of bumping your way over all of those speed humps for a short journey means you walk or get on your bike instead, some would say the zone has served its purpose.

But people would mind less if there was more persuasion and less dictation.

Who would argue with a 20mph limit near schools, at the start and end of the school day. Some thought to how the zones were implemented would win the PR battle.

And if we really want people to start getting on buses, having them cheap, regular and reliable would go a long way.

The 20's Plenty Campaign say they can do all this for relatively little.

There is one way to ensure we all drive slowly for fear of wrecking our cars, and that is to leave the roads to fall apart as they are now, with ever-deepening potholes the new speed humps.

We hope we haven't predicted the future.