A new report highlights that how implementing 20mph over a small area in Belfast where speeds are already below 20mph is far inferior to the established experience from city-wide schemes that reduce speed and casualties significantly. Hence this report gives little insight into the success of setting 20mph as an urban/village norm other than showing how not to implement it.

The implementation in Belfast was on just 76 streets in the city-centre on which the average vehicle speed was well below 20mph. Of these 76 streets, 27 were already fully or partially pedestrianised. At the same time other travel initiatives included the introduction of a rapid transit system and extension of the city-centre bus lane provision. There was also little community engagement or marketing of the 20mph scheme.

Such an isolated and small implementation which keeps 30mph as a norm on all the other streets in the centre was always going to result in little change and this report confirms this. In fact other reports which compared Belfast with Edinburgh and its city-wide 20mph scheme show just how more effective 20mph schemes are when implemented city-wide.

The contrast couldn't be starker. Belfast implements a small and isolated 20mph scheme in its city-centre and gets little change on congested streets where speeds are already low. Whilst Edinburgh goes city-wide delivering it to city-centre, suburbs, residential areas, shopping streets with engagement and education and gains a significant reduction in speeds and casualties. See these charts from a previous report by the authors that compares Edinburgh and Belfast 20mph schemes.

No doubt others will seize on this as evidence that "20mph limits don't work". But we would say that if any road change is implemented poorly and without reference to good practice then it will be sub-optimal with little benefits.

Across the UK local authorities are implementing 20mph as a norm for most urban and village streets with reductions in casualties of between 20% and 40% (Edinburgh, Calderdale, Bristol, Cheshire West and Chester, Bath, Warrington, and many more). On faster roads vehicle speeds are reducing by 5-6mph.

Key factors in successful 20mph implementations are :-

• Make 20mph the norm
• Deliver 20mph on driver's home streets
• Engage with the public on why it is being implemented
• Deploy on faster roads also for maximum effect

By ignoring these then it is no surprise that the Belfast implementation is showing minimal short term benefits.

To put it simply - Don't do it like Belfast, do it like Edinburgh.

Belfast has much to gain from learning from successful 20mph implementations in the UK. The Department for Infrastructure for Northern Ireland (the Highway Authority) should look to rolling out 20mph to all Belfast residents in a city-wide roll-out that mirrors the successes in England, Scotland and Wales.