New roads can cause congestion

Kate Ravilious in New Scientist:

Traffic should flow best in cities when only a limited number of roads lead to the centre. This counter-intuitive finding could allow planners to prevent gridlock by closing roads rather than building new ones.

It comes from a new way of thinking about complex networks developed by Neil Johnson, Douglas Ashton and Timothy Jarrett at the University of Oxford, UK. The researchers began by approximating a complex city network to just a ring road and a number of the arterial roads that cross at the centre.

They then worked out how the average time for journeys changes as the number of roads increases.

More here.