[revscat]

Why on earth would you think that that would ever happen?

[fractallyte]

Because governments could mandate it.

Yes, we're at the stage now where democracies need to become far more dictatorial, otherwise their populations will continue mindlessly along the path of 'Tragedy of the Commons'.

[tim333]

You don't even need dictatorial. Just tax breaks and the like for small light vehicles and penalties for large heavy ones.