Audi A3s fitted with S-tronic dual-clutch transmission and stop-start technology will cost from £18,300, and will hit UK roads in December.
Audi's stop-start technology was previously only available on four-cylinder manual gearbox models, but Audi has now expanded the range to to 1.4 TFSI and 1.6 TDI variants with the firm's S-tronic twin-clutch automatic transmission.
Audi's start-stop system for automatic gearboxes operates in the same way as its manual system, cutting the engine when the car is stationary and the brake is pressed, and refiring it in 0.2sec.
The system, which also takes energy generated under braking to charge the battery, brings a CO2 reduction of approximately 5g/km.
As a comparison, the A3 1.4 TFSI S-tronic with stop-start reaches 62mph from rest 0.1sec more quickly than its manual counterpart, in 9.3sec.
It also has a 3.7mpg advantage over the manual option on average, recording 53.3mpg to its 49.6mpg. CO2 emissions are 124g/km, versus the manual version’s 132g/km.
With the stop-start tech, the A3 1.6 TDI averages 67.3mpg (manual 68.9mpg) and has a CO2 output of just 109g/km.
Audi plans to expand the roll-out of its stop-start system on engines linked to S-tronic gearboxes in 2010, with further A3 models likely to get the system first.