Will air pollution will be increased by vehicles taking longer journeys?

The fundamental idea behind LTNs is that fewer short journeys are made by car, meaning less traffic and pollution overall.

Given the safer and more pleasant street environment created by preventing through-traffic, many people opt to make shorter (or longer) journeys by other means of transport instead. This has been shown to be the case following implementation of LTN schemes in Waltham Forest [12].

People moving under their own steam need to be able to take the shortest routes and will be able to pass through the LTNs by foot or on cycles or mobility scooters.

If people choose or need to use their cars they will have to make short detours in some cases. However, these slightly longer distances are likely to be offset by the predicted reduction in traffic overall, as recorded in other LTN schemes [13].

Another point to consider is that cars at junctions also produce emissions when idling as they queue to rejoin distributor roads from side roads, emitting pollutants as they wait.

This online public event held by Oxfordshire Liveable Streets gives us an insight into the experiences of a resident of Waltham Forest, where LTNs were implemented in 2015 [local detours are discussed from 21:00]:

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Research by King’s College London suggests that there has not been a decrease in air quality on main roads following introduction of LTNs in Waltham Forest [75 (page 8-9)], despite some vehicles having to make slightly longer journeys. This may be due to the overall reduction in traffic brought about by the implementation of LTNs, a phenomenon known as traffic evaporation.