Smarter Cambridge Transport

Does widening roads reduce congestion?

The answer seems obvious. Additional traffic lanes mean less congestion. But experience and behavioural psychology tell a different story.

People have a relatively fixed budget of travel time: on average 377 hours/year (within the UK), up slightly from 353 hours in 1973. Motorways and lower motoring costs (relative to earnings) have led us to ‘spend’ this travel time budget on travelling nearly 50% further than in 1973: longer commutes, more dispersed networks of family and friends, and venturing further afield for shopping, leisure pursuits and holidays. (Data from the National Travel Survey 2018.)

Another constant is people’s tolerance to congestion. Pick any decade since the 50s and you’ll find news articles moaning about the “intolerable” congestion. The thing is, enough people do tolerate congestion that they make it inevitable – what mathematicians call an ‘equilibrium state’. Typically, within five years after a road is upgraded, the traffic volume increases to a level where congestion is similar to before the upgrade.

In the case of piecemeal road upgrades, congestion is more often displaced than (temporarily) reduced. For instance, dualling the A10 from Ely will increase congestion on Milton Rd, the A14, A428 and M11.

This is why widening roads does not reduce congestion: it just increases the distances people travel. That’s not the outcome people stuck today in congestion actually want.

Is more travel good for the economy? In most respects, no: someone who commutes 50 miles to work is no more economically active than someone who commutes 5 miles. Do you spend more on food or clothes simply because you’ve driven further to buy them? However, there is one respect in which travelling further has an economic benefit: it gives employers a larger catchment pool to recruit from, increasing productivity and facilitating business expansion. This is the main economic justification for investment in roads and rail.

Politicians hear their constituents complaining about congestion; they hear businesses complaining about recruitment. They put two and two together and conclude the answer is to increase road capacity. Economists dutifully provide a cost-benefit analysis to support their decision.

In part two next week, I’ll explain what the correct conclusion should be and why.


This article was first published in the Cambridge Independent on 2 October 2019.

Edward Leigh

Edward Leigh is the leader of Smarter Cambridge Transport, chair and independent co-opted member of the Cambridgeshire Police and Crime Panel, chair of the South Petersfield Residents Association, business owner, consultant, and occasional blogger about making the world and Cambridge a better place to live.

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