SIR – Simon Grover believes that reducing speed limits on residential roads will make them safer ( Call for 20mph speed limits on county roads , Herts Advertiser, November 26). There is no evidence anywhere in the world to support that claim because such

SIR - Simon Grover believes that reducing speed limits on residential roads will make them safer ('Call for 20mph speed limits on county roads', Herts Advertiser, November 26).

There is no evidence anywhere in the world to support that claim because such measures bring with them a number of unwanted, unpredicted or unexpected consequences. Slower does not necessarily mean safer.

Drivers will generally comply with sensible limits. In the summer, I was driving through the main street in St Albans - the 20mph zone - at around 11.30pm. I was heeding the 20mph but the car behind became so frustrated that he soared past at what I estimated to be at least 40mph, and possibly 50, including pelican crossings.

My 23-year-old son (with an unblemished driving record) was as shocked as I was but we realised that the 20mph zone was a contributory factor to their behaviour.

Another side effect of 20mph zones is that pedestrians can feel "too safe" resulting in them stepping into the road without properly checking that it is clear.

Cllr Stephen Giles-Medhurst recently reported to the Herts CC Highways and Transport Cabinet Panel, "streetlights = 30" was a well-intentioned message but it seems to have led to drivers doing 30 when that may be quicker than is safe in some conditions.

In October, as my wife and I drove into Harpenden from the south, the car in front reduced speed to the 40 limit and I naturally followed.

The Mercedes behind us clearly felt that was too slow and overtook us both using the cross-hatching. I do not condone his manoeuvre but I believe the 40 limit starts too soon and contributes to dangerous driving.

Speed humps of various types cause damage to tyres, suspension and steering - how many accidents are caused by failure of these components damaged by road humps? Does anyone know?

Humps and other "traffic calming" measures can also slow emergency vehicles (especially ambulances where heart attack and stroke victims may not get to hospital in time).

Other measures can also have negative side effects. For example, cycle lanes can lead to vehicles passing bikes closer than they would if they had no separate lane, with consequential safety impact. This was the experience in Portsmouth, where their 20mph experiment has been anything but a success. I have a copy of the Interim Evaluation Report, which shows, among other things, a 35 per cent increase in pedestrians killed or seriously injured and an 11 per cent increase in injured cyclists!

Their public pronouncements may have trumpeted success but the reality is far less rosy. And at a cost of �572,988.

Finally, I am puzzled that Mr Grover suggests that 20mph zones would lead to less pollution - quite the opposite is the case.

I wholly support methods of improving road safety but they must be evidence driven, not based on surmise and misleading press releases from other parts of the UK.

ERIC BRIDGSTOCK

Evans Grove, St Albans

SIR - My heart was lifted to see that at last "Pressure is mounting for 20mph speed limits to be imposed on residential roads in the district".

I have campaigned for this through your columns and to the district council for more than 20 years. I was delighted when this limit was introduced into the city centre but it is long overdue for residential roads, especially those that have a school. Another idea I have proposed is to make these signs larger and flashing to draw to the attention of drivers that this speed limit means what it says in the interest of safety.

Well done The Green Party and others. Keep pushing!

FRANK LEMAN

Handyman Services

Slimmons Drive, St Albans