The number of permits issued which allowing Google to drive on public streets in California has more than doubled in the last month, from 23 to 48.
The figures come from California’s Department of Motor Vehicles.
Google has more than half the licences for driverless cars in the American state, with Tesla Motors the second biggest. Mercedes Benz has recently had two permits issued for it to test driverless cars.
Google has announced it is planning a new series of tests on cars near to its base in Mountain View.