Banwell Bypass

Key facts about new roads, bypasses and induced traffic, and their carbon cost

Banwell Bypass

Key facts about new roads, bypasses and induced traffic, and their carbon cost.

Induced traffic:

New roads create new traffic.  When a new road is built, new traffic will divert onto it.  Many people may make new trips they would otherwise not make, and will travel longer distances just because of the presence of the new road. This well-known and long-established effect is known as ‘induced traffic’.

  • In 1994 a Department for Transport commissioned report concluded

“An average road improvement, for which traffic growth due to all other factors is forecast correctly, will see an additional [i.e. induced] 10% of base traffic in the short term and 20% in the long term.”

 ( SACTRA Report 1994- Trunk Roads and the Generation of Traffic.  SACTRA were an independent panel of experts set up to advise the Department for Transport)

  • Higher than forecast traffic growth:  

In 2006 a Report for the Countryside Agency and the Campaign for Protection of Rural England by 3 independent transport consultants found that of 13 major road schemes

“Traffic growth on the routes considered was higher than forecast, sometimes quite dramatically so.”

In the case of the A34 Newbury Bypass, traffic levels increased by almost 50% in 7 years by 2003, not by 2010 as predicted.

  • Short and long term traffic growth:

In 2017 a Report commissioned by CPRE, Campaign for the Protection of Rural England, the Countryside Charity, found that road schemes generate traffic over the short and long term

‘ In the short run, 3-7 years after the baseline year, the mean increase in traffic was over 7%. In the long run,  8-20 years after the baseline year, the mean increase in traffic was  over 47%’.

( The Impact of Road Projects in England, 2017 by a panel of independent transport experts based on Highways England data on over 80 road schemes.    )

  •  The 2017 Report also found that for the 54 road schemes that opened between 2002 and 2010,  the 2014 emissions resulting directly from these schemes were of the order of 1.2 Megatonnes CO2 :

‘We estimate that this increase is very approximately 3% of the annual emissions of CO2 from all motorway and trunk road traffic in Englandxxviii.

 Another way of putting this is that it is the equivalent of putting an extra 590,000 cars with average mileage and average emissions onto the road. . This is a minimum estimate.’‘.

  • Embodied carbon emissions,

 sometimes called ‘capital carbon’ emissions, are the total carbon emissions from building a project, including emissions from the supply chain.

‘ Embodied emissions are the full supply chain emissions associated with the initial creation of an asset. Typically this includes emissions from: raw material acquisition, transport, processing and manufacturing of building materials; distribution of materials to site and energy used on-site in assembly. In the infrastructure sector these are commonly referred to as capital carbon emissions to accord with the concept of capital cost.’

Scott, Giesekam, Owen and Barrett (2015)

gives the  following information:

               7.1   There is a capital carbon standard, PAS2080, which defines capital carbon as greenhouse gas emissions that can be associated with the creation, refurbishment and end of life treatment of an asset ( for example a new road)

 “Capital carbon PAS2080 defines capital carbon as GHG emissions that can be associated with the creation, refurbishment and end of life treatment of an asset. This follows for all infrastructure sectors which have similar sources of capital carbon. This includes the emissions associated with the use of materials, such as concrete and steel, the use of construction plant, such as excavators or tunnel boring machines, and the transport of materials and plant to construction sites. This will occur for all construction activities be they directed to new build, maintenance or refurbishment. Capital carbon emissions also arise at end of life and are associated with demolition, waste processing and any final treatment/disposal. Carbon emissions from transportation which occurs as part of any of these activities is considered to be capital carbon

BSI (2016)

  •   There is a publicly available estimation tool to quantify embodied carbon in infrastructure projects, EE- IOA ( The top-down environmentally-extended input-output analysis)

A group of researchers at Leeds University have developed a methodology for the National Committee on Climate Change to provide an estimation tool that can be used to quantify embodied carbon in infrastructure projects (Scott, Giesekam, Owen and Barrett 2015)

 “EE-IOA generates an emissions intensity factor for the emissions embodied in UK construction per pound spent on the construction sector’s output (kgCO2e/ £), which we take as representative of the emissions intensity of infrastructure. This relates to all the physical goods and services required along the construction sector’s supply chains, whether produced in the UK or abroad

                7.3     Using this method, Professor Whitelegg calculated the embodied carbon cost of the  Shrewsbury North West Relief Road, based on embodied kgCO2 equivalent of 0.98 per £ spent, at 2010 prices, is 72,215 tonnes. ( £73.689 spent ( adjusted to 2010 prices) x 0.98kg = 72,215 tonnes)

  • It is possible to estimate the embedded carbon cost of the Banwell Bypass based on Professor Whitelegg’s method, but only approximately.   At this stage, the current estimated spend on the Banwell Bypass is £66 million.

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