The A27 Portfield work begins on Monday and will run to autumn 2020.
Lane widths will be narrowed on the A27 Chichester Bypass and A27 Westhampnett bypass and the speed limit reduced.
Roadworks will take place Monday to Friday during daytime hours and with nightworking kept to a minimum.
Work will be carried out on the A27 Chichester bypass, A27 Westhampnett bypass, Portfield Way, Shopwhyke Road and Oving Road.
The planned works form part of the planning permission for the new Shopwyke Lakes development, involving 585 new homes and community facilities to Shopwhyke Road.
A spokeswoman for the developers said: 'The A27 Portfield scheme is a major project which forms part of the planning consent for the Shopwyke Lakes development, benefiting the wider community, by enhancing pedestrian and cycle links throughout the local area.
‘Working closely with Highways England and West Sussex County Council, we have made every effort to minimise the disruption for local residents and businesses whilst we carry out the roadworks, but recognise that there is likely to be some disruption for those travelling on the affected roads – particularly during peak hours.
'We’d like to apologise in advance for any disruption experienced during the planned works, and encourage the local community to visit a27portfield.co.uk, where they can find out the latest information on the roadworks, along with answers to any questions they may have.'