Hey, where's the roadside test for vicodin? Prescription codeine or morphine? Dextromethorphan?
I am sure they would like to have one, but I think there are two factors to consider when asking why these drugs are allowed exist without it:
1. They're not legal unless prescribed by a physician. Which makes them controlled and, in theory, harder to get. So less pill heads driving compared with drunks.
2. They have a valid medicinal use which is weighed against the risks driving while on the substance.
Anyhow, it's a real issue and I think a reliable field test would go a long way towards helping the cause.
The biggest difference between time and space is that you can't reuse time. -- Merrick Furst