The effectiveness of using non-charging measures alone to lower NO2 to legal limits was assessed as part of our technical work. Bristol City Council has achieved some success in reducing car trips over recent years, by promoting use of sustainable travel. Since the Air Quality Action Plan was published in 2004, there has been a sharp increase in cycling and use of public transport in Bristol. However, despite this improvement, demand for travel by car has risen due to population growth and rising economic activity in Bristol. Non-charging measures have not been sufficient to achieve compliance to date.

If we take the example of Metrobus, previous modelling estimated that this very large scheme will lead to a drop of NO2 concentrations by a maximum of 5% at some locations. This is equivalent to approximately 4µg/m3 at Rupert Street. However, at this location a drop of 20-30µg/m3 is required to achieve compliance with legal limits. Additionally, a scheme of the scale of Metrobus has taken 6 years to deliver, from initial planning to completion. This would be too long for meeting the government’s requirement to achieve compliance in the shortest time possible.

To test the impact of using only non-charging measures in Bristol, an ambitious target was assumed for the Clean Air Plan; that a reduction of 5% in traffic levels could be achieved within 2 years. This assessment found that with this level of traffic reduction, the year we expect to achieve compliance would not change from the baseline case (or ‘do nothing’ case) year of 2025.

Sufficient non-charging measures are unlikely to be deliverable in the short term or be quicker to deliver than a charging scheme. The Council has been directed to achieve compliance in the shortest possible time, and therefore non-charging measures will be used to complement a CAZ, or as an alternative to a CAZ, and where possible designed to mitigate impacts.