Cities worldwide watch London to see if Ulez can get up to speed

Beside the obvious environmental benefits, one of the key questions for those following the expansion of the scheme is whether it adds up financially

The controversial expansion of London's ultra-low emission zone (Ulez) on Tuesday will be watched closely by policymakers around the UK and the world, as other cities weigh up whether to introduce similar schemes.

One key question is whether low-emission zones make financial sense for cities that introduce them. City administrations must weigh up the health benefits, any income from tolls and fines, the positive and negative effects on businesses and the cost to affected residents.