Yes, reducing the amount of time vehicles spend queuing and stop-starting is likely to help with the air quality problem. However, measures to reduce queueing typically rely on providing additional road space or re-distributing priority at junctions. These kinds of measures are known to attract additional vehicles. This has been experienced across the country as well as in Bristol, and is known as traffic inducement. Consequently, measures to improve vehicle flow may have a negligible impact on air quality, or even worsen the problem, by increasing the number of vehicles using the cities roads.
There are also practical considerations to account for – many of the streets in Bristol are very narrow and cannot be easily widened to improve flows.
One of the non-charging measures being considered as part of the plan is soft traffic gating, which involves a real-time traffic management system in the city. This option could help improve how our road network responds to congestion by producing better coordination between traffic lights in response to current real time traffic data, thus reducing queuing and stop-start traffic movements. However, such measures are unlikely to be sufficient to achieve compliance in the shortest possible time without the addition of other measures such as a Clean Air Zone.