They do test the blood, but the tests are not 100% accurate (no medical test like this is). Asking people helps reduce the need for these tests which helps redu

They do test the blood, but the tests are not 100% accurate (no medical test like this is). Asking people helps reduce the need for these tests which helps reduce the accidents caused by inaccurate results. Give people an incentive to lie and these accident rates will go up. It's as simple as that.