Most modern transmission already do this.
ZF calls it Neutral Idle Control and all their 8HP units have it. AISIN calls it Automatic Neutral Control. All GM transmissions since the 6Lxx/6Txx have had a neutral idle feature.
The transmission control module releases whatever forward clutch it needs to when vehicle speed is 0, effectively putting the transmission into a neutral state without moving the manual valve or whatever controls the transmission range. Because the torque convertor isn't shearing fluid in neutral, engine load and fuel consumption is reduced ever so slightly. It's a no-cost fuel saving solution that only requires a software strategy to implement.
If you've ever felt a tiny bump while transitioning from the brake to the throttle from a stop, like when you're starting to pull into the garage after waiting for the garage door to open, that's the transmission coming out of neutral idle. It is typically imperceptible on level ground but the slight incline of a driveway makes it just noticeable enough if you're really paying attention.
ZF calls it Neutral Idle Control and all their 8HP units have it. AISIN calls it Automatic Neutral Control. All GM transmissions since the 6Lxx/6Txx have had a neutral idle feature.
The transmission control module releases whatever forward clutch it needs to when vehicle speed is 0, effectively putting the transmission into a neutral state without moving the manual valve or whatever controls the transmission range. Because the torque convertor isn't shearing fluid in neutral, engine load and fuel consumption is reduced ever so slightly. It's a no-cost fuel saving solution that only requires a software strategy to implement.
If you've ever felt a tiny bump while transitioning from the brake to the throttle from a stop, like when you're starting to pull into the garage after waiting for the garage door to open, that's the transmission coming out of neutral idle. It is typically imperceptible on level ground but the slight incline of a driveway makes it just noticeable enough if you're really paying attention.