The four-year campaign, funded by the Department for Transport, will see Forster promoting greener alternatives.
Worcestershire is one of three areas testing the effectiveness of PR for public transport. Darlington and Peterborough have already started their campaigns.
If effective, the DfT will extend 'On the Move in Town' nationwide.
Forster will work with the council's 'Sustainable Travel Town Team' to try to cut single occupancy car trips by ten per cent. The council also wants to limit the school run and increase 'park and ride' and cycling.
The target is to boost the use of public transport by 20 per cent over four years.
'Climate change is a major issue and we have to think about getting people off the roads,' said Forster head of creative services Tracey Collinge.
She added that attitudinal research will precede the creation of local 'champions for car sharing'.
'We want people to feel empowered and that they are making a difference in their town,' Collinge said.
WAR will target families with children via women's weeklies and tabloids.
SodaStream now sells chrome-finished machines as well as 1980s-styled plastic models. It also offers low-sugar versions of its drinks.
WAR has replaced Birmingham-based HotHouse Integrated Marketing on the account.
The agency's Solihull office is handling both consumer and trade PR for the Birmingham-based company, which plans to add 20 stores to its current estate of 128 outlets this year.
The agency was hired following a non-competitive pitch to promote the chain, which also plans to develop a 'contract specialist' division.
Floors-2-Go, founded in 2000, is spending around £7m on marketing this year, with PR a 'sizeable six-figure sum', the agency said.
McCann Erickson is understood to be the first PR agency used by Floors-2-Go, which markets itself as 'the one-stop wood-floor shop'.