Reliability and Validity Scenario

Imagine you are a part of a group tasked to reduce DUI incidences in your area. Your local law enforcement has decided to set up mandatory check points on four roadways that leave the local college town. These DUI check points are conducted one Friday a month from 10:00pm until 2:00am. Local residents are concerned that these mandatory checkpoints might causing more harm than good and would like to discuss how valid your plan is as a means of reducing DUI in your area. Given this scenario try to explain how you define the key variables under the influence and checkpoint to make sure your study will be both valid and reliable. Furthermore, address the following questions from your local residents:

Content validity- what drugs will you be checking for with your DUI checks and why?
Construct validity- how will you define under the influence, and why?
Face validity- what will the checkpoints look like to drivers passing by and why?
Test-retest reliability-will there be a difference between road sobriety checkpoints and measured data at the station?
Inter-rater reliability-if two officers disagree as to whether a driver is under the influence, how will you break the tie?
Error- what will you do to reduce the likelihood of false positives for your DUI checkpoint