Low lives

In your 4 July report of MSP Mark Ruskell’s Bill proposing reducing the urban speed limit from 30mph to 20mph, you failed to point out that the Bill would allow local authorities to increase the limit back up to 30mph in areas “where they and the local community consider it appropriate”.

20mph is a suitable speed for local side roads (in most cases it is not possible to drive any faster, making one wonder why a lower limit is necessary) but it is a ridiculously low speed on major through routes; it is only appropriate in city centres.

In Edinburgh, in my area, major through routes will remain at 30 or 40, but the City Council has seen fit to impose a 20mph limit on a section of Slateford Road (an A road and a major artery and bus route). Sensibly, most traffic ignores that limit; even the buses ignore it.

So if this lower limit makes no difference to driving habits, why bother with it? All that expense to no effect!

One may also ask what evidence there is that driving at 20mph reduces vehicle emissions (one of the purposes of Mr Ruskell’s Bill). Logic suggest that emissions will increase because of the lower gears involved and/or lower efficiency at low speeds.

STEUART CAMPBELL Dovecot Loan, Edinburgh

Why is there a call for a countrywide 20mph speed limit in towns and cities?

I imagine those calling for it believe that this will cut pollution by a third. Sadly, they are woefully wrong, for a very simple reason: any car travelling at 20mph rather than 30mph will have its engine running for an extra 50 per cent of the time, eg a journey of 10 miles will take 30 minutes instead of20minutes. Sothepollution will be less, but for a longer period of time. Back to square one, I fear.

Much better to employ smart traffic lights at all junctions, which detect the flow of traffic, and reduce the vast amounts of time wasted at junctions when there is no traffic flowing the other way. ANDREW MORTON

Park Place, Dollar