Better Shrewsbury Transport say the town's £81 million North West Relief Road will not ease drivers' woes, and traffic will get worse into the late 2030s.
The claims come after new traffic modelling was released by Shropshire Council, commissioned as part of the Local Plan for the county.
Dave Green, spokesman for the campaign group, said: "Anyone who thinks the North West Relief Road is going to solve Shrewsbury’s traffic issues had better take a long hard look at this report. The figures are a shocking reality check and spell out misery for drivers over the next fifteen years.
"Shropshire Council’s eagerness to build car-centric housing developments means that our roads will be clogged full of traffic, even if we spend millions on the NWRR. Unless we change course, the future is one of endless traffic jams, congestion and total gridlock."
He added: "The council’s promise that the North West Relief Road will save Shrewsbury from traffic chaos is a fairy tale. It isn’t supported by the new figures at all. To give just one example, the modelling shows that the proposed 450 new houses west of Ellesmere Road will generate as much traffic as the NWRR would remove, cancelling out the benefit of the multi-million pound new road.
"Better Shrewsbury Transport is calling on the council to abandon its outdated, car-based development plans and focus on making Shrewsbury a better place to live by encouraging public transport, walking and cycling. If we can’t solve the town’s traffic issues by spending over £100m on a new road, we have to start reducing traffic instead. A proper local plan would focus on reducing car journeys by 10-20 per cent as Scotland and Wales are currently looking at. If Shropshire Council insists on continuing on its present course, the county will end up spending tens of millions on a new road that won’t even do the job it’s supposed to."
The council's highways modelling can be viewed here: shropshire.gov.uk/media/21281/shrewsbury-highway-modelling-ev100.pdf
Public hearings into Shropshire Council’s Draft Shropshire Local Plan (2016 – 2038) start at the Sovereign Suite, Shrewsbury Town Football Club neat Tuesday, July 5.
A Shropshire Council spokesman said: "The continued growth and prosperity of Shropshire and Shrewsbury is vital for its residents, visitors and businesses, and the infrastructure needed to support this is an ongoing and developing process.
"The modelled reduction in traffic from Shrewsbury town centre streets to the outer ring road, when the North West Relief Road is complete, is a key opportunity to really push active travel and get even more people walking, cycling and using public transport in the town centre and on key corridor routes into the town centre. Many of these corridors routes will, in time, support future developments in the town and provide the infrastructure for car-free local travel.
"Working alongside wider council priorities such as the Local Transport Plan and the Local Walking and Cycling Infrastructure Plan), both the NWRR and the emerging Local Plan will also help address issues around electric vehicle charging infrastructure, air quality, green hydrogen infrastructure, transport-related carbon impacts and traffic accident rates.
"Further details on the traffic modelling and future forecasts will be in the NWRR Full Business Case submission to DfT, which is expected in December 2022."