FOR 70 years road planners have appreciated the trade-off between the economic and social benefits of the motor vehicle and the chemical and noise pollution costs.

The bypass has been the favoured response to the issue - keeping pollution away from people and reducing delays.

For more than 40 years, Lancashire highway engineers protected such a route for traffic from the M6 to Morecambe. A bypass at low level alongside the Lune, on ground unlikely to be wanted for housing, was the choice.

When the pollution reduction and time saving benefits were judged to match the cost of construction, it would be built. No other route was guarded.

Then, last year, Lancashire Cabinet member Cllr Jean Yates suddenly bought in another consideration - the life of a colony of small amphibians. The value of this was considered by her to be so great that the Western by-pass would never be economically justified.

City Council Leader Cllr Ian Barker gave his full support and both reneged on what they had put in their manifestos.

Now some people are suggesting there is a route to the north that is as good. Agreed, it would reduce some heavy vehicle pollution in central Lancaster, and slightly shorten journey times for M6 to harbour traffic. But it will not shorten delays for commuters and will not reduce the pollution along Morecambe Road.

Unlike the Western route, it requires a lot of cut and fill, with ugly roundabouts on the side of Beaumont Vale in the green belt, harbour traffic grinding up Cross Hill and then crossing the A6 at high level, with permanent noise pollution for a significant number of houses in Slyne. Finally, it will dive down to the Lune, creating a scar that will be visible from all high ground south-east of the Lune.

Do not let us pretend that this northern route is anything like an alternative for the carefully planned Western bypass. Rather than reducing the polluting traffic through the villages, it will increase traffic in Slyne-with-Hest and Bolton-le-Sands.

I doubt it can ever be economically justified, with it having so few pollution-reduction benefits, and a tremendous and ugly visual impact. Once more Labour and their political allies have put the clock back for Lancaster.

M R Jackson. Hest Bank.