What is more practical in a built up area than a 20mph zone? and how is driving at 20mph not practical?
There's plenty of reasons against.
1) 20mph in a car is very inefficient, in terms of fuel consumption. This means a rise in emissions. I don't mean OMG CO2 aka breathable air for plants. I mean all the other emissions that come from cars, nitrous oxides, hydrocarbons, carbon monoxide etc. These are the emissions that cause smog and are alleged to cause or aggrivate asthma. If the cars go through at 30 then you're less likely to get asthmatic children, or to trigger an attack in an affected child. Young children can die from asthma attacks if they don't know they have it, or the parent isn't around to provide the inhaler. For this reason alone all 20 zones should be removed, after all if it saves one life it's worth it, right?
2) 20mph
zones* are required to be self enforcing with speed bumps or other forms of traffic calming. This further exacerbates the inefficiencies and pollution issues as cars have to speed up and slow down to negotiate the obstacle course. It also creates noise as cars hit the bumps and perhaps more importantly it creates vibration which can and does damage houses, especially older terraced houses built in Victorian times
3) Driver distraction. For a human to do well at a task, any task, it needs to be sufficiently interesting and challenging to keep the mind focussed, otherwise people lose concentration, the mind wonders and mistakes are made. If the task in question is just typing up letters then you'd get a few spelling mistakes creep in, but if the task is crawling at 20mph through a mostly deserted residential street at night then you may not notice the goth kid dressed in all black who just decided to cross the road without looking because you wern't paying attention. (This is the same argument against lowering motorway and A-road speed limits BTW)
Oh and to the person who made the tinfoil hat comment on the last page. Don't worry, there are already plans to put SPECS cameras at the entry/exit points on 20 zones, meaning that the only people who can speed in those zones are people who live there, or joy riders who don't intend to leave that zone. edit: or don't own the car they're driving.
edit: As for the 8% reduction, once all the residential areas are dropped to 20, that 8% reduction will disappear as people resume using their original routes that they used to use as there's no benefit to avoiding the early 20 zones any more. If you don't believe me then look at the effect of the western expansion of the congestion charge zone. All the people who live in the newly expanded area can now drive into central London for cheap again, so they do so, and congestion has increased. Now imagine that zone increased to cover the entire south east and we'd be right back to where we were before it was first put in.
* Please note the difference between a 20
zone and a 20
limit before replying to say that the 20 section by you has no traffic calming.
