Study finds some road closures cause less congestion

Media Relations Team, 19 August 2021

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Cars on the street

Two researchers from the University of the West of England (UWE Bristol) have published a study shedding new light on why traffic is sometimes reduced when certain city roads are closed by the Council. Dr Steve Melia and Dr Tom Calvert from UWE Bristol’s Centre for Transport and Society found that if main or ‘strategic’ roads were closed, some drivers decided to stop using their cars and instead used different forms of transport, or changed their travel habits.

Since the first lockdown, many councils have been closing roads to car traffic, converting them to pedestrian walkways or reserving them for buses and bikes. For the study, the researchers looked at other similar trends from evidence around Europe, and two recent examples in Southwest England.

Earlier studies had shown that when roads were closed, some of the traffic usually ‘disappeared’ but until this latest study the reasons behind this were uncertain. Steve Melia, who is Senior Lecturer in planning and transport, said: “We found that if you close a local road with easy alternatives, nearly all the traffic is displaced onto those surrounding roads and there may be no traffic reduction. 

“But if you close a strategic road, causing a big detour, then some of the traffic does ‘disappear.’ Traffic volumes go down, partly because congestion increases, at least in the short-term. Some people switch to public transport, walking or cycling, while others travel less or go somewhere else. In the longer-term, there’s some evidence that traffic volumes continue to fall, gradually reducing the congestion.”

He added: “This creates a dilemma for local authorities. The easy road closures might help to improve the feel of a street, but they do nothing to reduce traffic. The bigger, more controversial closures do cause some congestion, at least to start off with, but they’re the ones that bring the benefits of less traffic across the city.”

An example of a local road with easy alternative is the pedestrianisation of St James street in Taunton town centre in 2019, which is featured in the research. Some 98% of the drivers who used to drive along St James Street continued to drive to the same place but took a slightly longer route. There was little evidence of behaviour change and no traffic reduction.

That same year, in the centre of Bristol, a five-day demonstration on Bristol Bridge caused the strategic closure of the bridge, the only route for traffic to cross the city centre. The alternative routes were longer and already congested. Over the five days of demonstration, congestion increased slightly and the volume of traffic fell by seven per cent in the city centre and two percent across the rest of the city. Bristol City Council has since installed a bus gate on Bristol Bridge, permanently removing cars and vans.

Research Fellow Tom Calvert said: “The Taunton project had to adapt to fewer roads being pedestrianised than expected. It was a reminder of the constraints and objections that pedestrianisation schemes can encounter. Nonetheless, the combination of the two studies made a valuable contribution to understanding the realities of traffic displacement and reduction.”

The research also used evidence on the pedestrianisation of the right bank of the River Seine in Paris in 2016 (already published but not in English). This showed a similar pattern to the Bristol example, but the authorities found a different reaction in the short and medium terms. Over the following year, traffic volumes on the surrounding roads continued to fall.

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