Luther won the brief after a five-month long pitch against four agencies, including incumbent Countrywide PorterNovelli.
The agency is to work with EST's clean fuel scheme, called TransportAction, and arm Energy Efficiency to persuade firms to save energy.
Luther will promote clean fuels to fleet and truck operators, alongside highlighting the value of energy efficiency as a marketing tool to companies installing, manufacturing or selling household products such as fridges and boilers.
Luther partner Ben Rich, who co-heads an eight-strong account team, said: 'Part of the messages we'll be working with EST on is to help people understand that it isn't just about doing something good for a pat on the back - there's a real business threat if they do nothing.'
He said plans for congestion charges based on vehicle emission levels and low emission-only zones in cities across Europe could affect the competitiveness of companies.
Luther reports to Transport Action PR manager Penny Andrews and EST corporate comms head Margot Marshall.