Every time this is brought up people say &quot;there is no effective way to test impairment&quot;. What ever happened to good old &#x27;walk the line&#x27;. Road-side maneuvers are still used extensively with suspected DUIs, but the logic is that if you can perform the certain complex set of tasks they give you, you are fine to drive.<p>How is this any different for weed, or anything else?