YES! Under Pennsylvania law, if you are driving a vehicle and if you get pulled over, then a police officer may request that you submit to a blood or urine test if he reasonably suspects you are impaired or if he has reasonable suspicion that you may be under the influence of drugs or alcohol. If the blood or urine test comes back positive for marijuana (any amount above 1ng/mL), then you are considered to be driving under the influence of a controlled substance and you may lose your driver license.
You ask: How can I get a DUI if I wasn't smoking pot that day? That is a great question, however, the current law doesn't consider impairment in determining a violation. You may get a DUI if you smoked pot two weeks ago and haven't touched drugs since.
The problem behind the current DUI statute, as proscribed in Pennsylvania, is that police and prosecutors use a system similar to the DUI, Blood-Alcohol-Content (BAC), calculations. Unlike alcohol, however, marijuana (THC) absorbs into the blood stream at a much different rate. For example, someone who smokes marijuana on Friday night would almost always have enough THC in their blood the following Monday morning to be found guilty of DUI in Pennsylvania. Conversely, if a person drinks eight beers on Friday night, then they wouldn't have any alcohol in their system on Monday morning and thus could not get a DUI for alcohol impairment.
The DUI law provides police and prosecutors an opportunity to charge citizens with DUI even though they aren't driving impaired! This is illogical and unjust! In practice, anyone who smokes marijuana either legally (such as for medicinal purposes in a state where marijuana is legal) or illegally is guilty of DUI if they EVER get behind the wheel. Many citizens are therefore constantly driving under the influence of drugs!
While other states (New Jersey, Oregon, Colorado, etc.) allow their citizens to use marijuana for recreational and/or medicinal purposes, the Pennsylvania law could imprison those same American citizens for the very same conduct which is lawful in Pennsylvania.
The purpose of the law contradicts the title of the law!
For more questions or concerns regarding the DUI law in Pennsylvania, contact Patrick M. Rogan or Daniel J. Mulhern at Rogan Law in Scranton.