[SPF2245]

1) Most states allow for DUI arrests on PUBLIC property as long as this term applies, "public access". Meaning, if the general public has access to the property, it's fair play.
2) Reasonable suspicion allows an officer to make an investigative traffic stop to further probable cause, it's not always as clean if abused, but it works. Example, wandering in a travel lane without actually leaving the traffic lane (a violation) coupled with varied speed is enough to articualate a stop based off "reasonable suspicion", again, not all states/juristictions. And another LE observations of a driver (in a drive-thru for example) is another case supporting a stop. Most states stop abuse of this by stating the stop must be concluded when the grounds for the stop have been justified to stop "fishing expeditions. Example, a stop for a seat belt in some states does not allow for any other investigation unless something new pops up during the contact.
3) Is it really such a bad thing to get drunks off the road? What would you rather we do, wait for a traffic accident? No thanks, every chance LE gets to remove a drunk from the road, the better for everyone.