Well, they have a speed they're comfortable with, AND an amount over the limit by which they feel (legally) 'safe' at. All this proves is that they don't want

Well, they have a speed they're comfortable with, AND an amount over the limit by which they feel (legally) 'safe' at. All this proves is that they don't want to go much more than 10 over the limit, AND the speed at which they feel safe is at least (but maybe higher than!) 80mph.