It may not reduce drug abuse, many drug users do not have to use cars or they just use public transportation, so you are begging the question in asking me to defend a policy that reduces drug abuse, because that is an assumption that I don't think the policy proposition has earned.
Now you're confusing 'significant impact because most drive' with 'but a small percent of people don't', along with ignoring the other areas people would be confronted, and also ignoring the larger issue as I explained above, that it's not about the details of the test.
Hopefully you respond to my question about something like a parenting license, I'd like to gauge what you find acceptable levels of government involvement in our lives to be.
Your parenting license is an interesting idea - you didn't suggest it as it's often discussed, as in 'people have to take classes and jump through hoops to prove they have the right to raise children'. That has long been popularly opposed as excessively intrusive about what is a fundamental human activity (to not quite call it a 'right'). I'm pretty hesitant about being intrusive there, despite the benefits.
But it's an interesting idea about a drug test for parents. My first reaction is favorable towards it, as my quick balancing between intrusion vs. benefit.