It seems logical that the answer to road traffic congestion is to build more road space. The evidence shows this doesn’t work.
Much of the discussion about the A27 is based on outdated thinking. Here are some of the issues and the facts. (Information sources are listed at  the bottom and indicated in brackets)

Traffic

It seems inevitable that as the economy and population expand, so must road traffic. This is not true. Traffic levels on the A27 are similar now to levels in the late 90s (1). Since then 7,000 homes were built in Arun District and the economy has grown by around a third (2).

Most traffic on the A27 travels less than  15 miles.

Increasing road capacity increases traffic levels.  New roads generate:

• traffic from other roads (which can be a good thing);
• new trips (previously suppressed due to congestion); and
• longer journeys (particularly by commuters).

Those new and longer journeys have to start and end somewhere, so increased capacity also generates more traffic away from the new road, in residential and business areas. (3)

Old thinking was that building development generates increasing traffic and the need for more road space. Evidence shows that it is road building that generates more traffic and increases building development. This largely happens by making longer distances commutable and creating demand for housing further from workplaces and space for business and retail areas accessible by lorries.

Pollution

Highways England (HE) and Department for Transport (DfT) studies (4) say that traffic levels within Arundel itself will not reduce with the building of a bypass, but are likely to slightly increase due to the increased traffic.

The future

Digital technology is changing business, shopping and working patterns, meaning conventional patterns of travel are changing.
Car driving has declined in the UK over the last 20 years, particularly amongst younger people. For men below the age of 35, this fall is by nearly half. (5) Cars are not aspirational for the young any more, just practical tools.
Technologies are now available for more cost effective, better value, smart transport management systems for all transport modes.

Everybody drives now?
Not so. Over half the population of Arundel does not have access to a car for much of the time! Nearly two thirds of households h

Solutions
The answers to traffic problems around Arundel lies within the urban conurbations along the south coast.

Long term solutions are in better urban land use, improvement sustainable transport and a walking and cycling environment, freeing up large areas of car park land for development.

1 www.dft.gov.uk/traffic-counts, Department for Transport (counter data).
2 www.ons.gov.uk/economy, Regional GVA NUTS3 1997-2015 south west Sussex
3 Standing Advisory Committee on Trunk Road Appraisal, 1994 (and others)
4 SoCoMMS, Halcrow, 2002; A27 Feasibility Study Report 3 (5.4.4), Parsons Brinkerhoff, 2015
5 Recent trends in road and rail travel: What do they tell us? Independent Transport Commission, 2016
6  Travel Fast or Smart? A Manifest for and Intelligent Transport Policy, David Metz, 2016