Research shows forecasts rarely come true

A recent study of new road reviews shows that the costs and effects

of new roads often confound official predictions

The Highways Agency reviews new trunk road schemes one year, and then 5 years, after they open - to assess how accurate the original traffic, economic and environmental forecasts were.

A helpful new report by the Campaign for Better Transport looks at four of the most recent 5-year-after reviews:

A6 Great Glen Bypass in Leicestershire
A650 Bingley Relief Road in West Yorkshire
A11 from Roundham Heath to Attleborough in Norfolk
A27 Polegate Bypass in East Sussex

The report compares these findings to a study of 28 one-year-after reports.

More traffic

The reviews found that overall traffic levels rose significantly as a direct result of each scheme. Two out of the three bypasses moved the congestion elsewhere. And many nearby roads also saw large increases of traffic.

Traffic along the A6 corridor increased in the 5 years after the Great Glen Bypass was built. The number of vehicles using the combined new and old A6 is 15.5% higher than the traffic which formerly used the old A6 alone.

Benefits fall short

The economic benefits of the schemes have not always matched predictions either. For the A6 Great Glen Bypass, the monetary benefit of time savings is calculated as £18.5 million, about half that predicted.

The accident benefit is £20 million, 23% lower than predicted.

And the bypass has adversely affected a few businesses on the old A6 which relied on passing trade.

What about cycling and walking?

Although many of the schemes provide facilities for walking and cycling there seems to be no increase in these.

Walking and cycling levels are not monitored afterwards - something CPRE has raised with the Highways Agency.

These results are typical

In 2008 the Highways Agency commissioned transport consultants Atkins to examine 28 of their own one-year-after reports.

They found only 40% of bypass schemes have predicted traffic volumes within 15% of the actual volumes, while 'over half of the scheme models have under-predicted traffic volumes on the old route'.

Atkins also found that the calculations of economic benefits were lower than forecast:

overall actual accident savings on bypasses are about a third lower than predicted
only 42% of predicted scheme costsare within 15% of the actual costs
average benefits have only been worth 2.6 times the cost, less than the 2.9 times predicted

But this masks large variations: only 'a very small number of schemes have an [actual] benefit cost ratio that was close to predicted'.

Interestingly, separate consultants paid by the Department for Transport to audit regional and sub-regional transport models found in 2009 that just one in four models is suitable for highways schemes, and one in seven for public transport schemes.

Using these figures to show how road schemes don't always fit the forecast
could be very helpful in throwing out controversial schemes.

From an article in the April 2010 issue of Fieldwork, CPRE's member newsletter

Fiona Cowan
19 May 2010