With the traditional gearboxes in most US vehicles you're using a lot more fuel.
If they were changed over to manuals, it could save quite a bit.
Swapping them over for dual-clutch transmissions, you could be as good or better than with the manuals - especially with drivers that aren't used to manuals
On the Euro NEDC, these automated manuals are starting to get better mpg numbers than their manual counterparts.