Thread by @RobBryher

Right, it's time to debunk the widely held view that closing roads to traffic just displaces traffic onto surrounding roads and so is undesirable. (All of the following is from Cairns, S., Atkins, S, and Goodwin, P. (2002) "Disappearing traffic? The story so far.")

The image shows the recorded changes in traffic levels from 63 individual case studies where roadspace was removed. 51 showed a general traffic decrease in the surrounding area, and only 11 showed a traffic increase.

Quote: "...in half the cases, over 11% of the vehicles which were previously using the road or the area where roadspace for general traffic was reduced, could not be found in the surrounding area afterwards."

Professionals surveyed thought an 11% traffic reduction might be achieved by a general roadspace reallocation scheme in their area and an 8·8% traffic reduction might be achieved by introduction of a bus lane. Only 3% thought these measures would result in zero traffic reduction.

So:
> traffic reduction is a real phenomenon
> levels of traffic reduction that occur from reallocating roadspace can be quite high
> most transport professionals support the concept of traffic reduction

The behavioural reasons for this are complex, but three stages can be identified:
1) "road capacity has been reduced"
2) "adequate spare capacity on other routes/times of day"
3) "no adequate additional capacity on other routes/times of day"

Short-term responses to 3):
> change of travel mode
> choosing to visit alternative destinations
> changing frequency of journey
> consolidating trips
> altering allocation of tasks within household for more efficient trip-making
> car-sharing
> no longer making journeys

Longer term responses to 3):
> changes in job location
> changes in household location
> changes in developers’ choice of location for new development.

Responses differed between individuals and places. Conventional assumptions about behavioural change are inappropriate.

"Nearly 60% of professionals agreed with the statement that ‘roadspace reallocation, or its effects, could ‘tip the balance’ in a decision mainly being
made for other reasons (such as whether to move job or where to move house)’."

Professionals also thought that [roadspace reallocation] was an underlying prerequisite since other measures, such as cleaner vehicles, smaller cars and vehicle routing technology would not be sufficient to achieve levels of congestion and pollution reduction that are desirable.

Oxford Transport Strategy resulted in 20% reduction in vehicles entering the central area. Number of people arriving and parking declined by about 700–800 a day, but the number arriving on buses increased by about 2.000 - so overall number of people visiting the centre increased!

In conclusion, reducing road space more often than not results in a reduction in overall traffic of (on average) 11%. You can reassure anyone concerned that a road closure will push traffic onto surrounding streets with this high-level evidence that it is not necessarily true!