Which is less polluting: driving 2 miles across the thinly populated centre of Birmingham, or driving 3 or more miles round the more densely populated outside?

The A4540 ring road marks what will be the outer boundary of central Birmingham's new Clean Air Zone. Proposals now before local councillors mean that a charge of £8 will be levied for most diesel cars made before 2015 and most petrol cars manufactured before 2006. Buses, coaches and HGVs will pay £50.

The plan means that high-pollution vehicles on cross-centre journeys will now avoid the charge by driving round the ring road, meaning at least 3 miles of motoring in the centre of the city, rather than paying the charge to travel 2 miles directly across the zone to get from one side to the other.

Angry opposition councillors confronted the plan's proponents, as up to 10,000 mostly crticial comments on the scheme were debated, the Birmingham Mail reported.

Council leaders confessed that the Clean Air Charge would not reduce pollution levels quickly enough to meet government targets. Parts of the city will be compliant in 2020, more in 2021 and the rest in 2022.