Heavy duty truck MPG

What would be interesting is a controlled crowd sourcing approach.

Your modern car/truck knows it's speed, throttle setting, fuel usage etc... Rather than an EPA estimate, it could provide an array of data when hooked up to a diagnostic system (or via radio using newer Connected Vehicle systems). This array would give MPG under a massive variety of conditions.

You could then plug in your driving behavior (retrieved from your car/truck) and it would estimate based on your driving patterns, what you could expect in terms of fuel economy.

This would circumvent a VW type situation as they can't depower the engine for the test since effectively you would have near 100% of all data.