Your not being arrested for being intoxicated. You are being arrested for operating a vehicle under the influence. Operation of the vehicle gets you arrested at a check point. Officers are also observing you operate the vehicle when you enter the check point. When they stop you, they should be observing for physical indicators of intoxication...odor, slurred speech...then administer a field sobriety test....failing, then arrested. All under observation at the time of the alleged violation.