WASHINGTON, November 16 - RAPSI. Recreational use of marijuana will soon be legal in the US states of Colorado and Washington, which has sparked debate over how to police the new laws as officials worry that more impaired drivers will be on the road.

“Marijuana is new, so it’s going to take some time to figure out how the courts and prosecutors are going to handle it,” said Washington State Patrol spokesman Dan Coon, the Associated Press reported.

The laws legalizing marijuana in Colorado and Washington were passed by voters last week, and will allow adults over the age of 21 in both states to buy or possess marijuana legally for recreational use.

Officials are concerned about road safety because more people could be driving while under the influence of marijuana, but Coon said “the key is impairment: We will arrest drivers who drive impaired, whether it be drugs or alcohol.”

The law passed in Washington does change driving under the influence (DUI) provisions by establishing a new blood-test for marijuana if impaired drivers are pulled over by police, but Colorado’s measure did not make any changes to its DUI laws.

Driving while under the influence of drugs has always been illegal, but setting a benchmark for marijuana that can be compared to blood-alcohol limits has generated intense disagreement, the AP reported.

“There is not yet a consensus about the standard rate for THC (Tetrahydrocannabinol) impairment,” said Betty Aldworth, advocacy director for Colorado’s Campaign to Regulate Marijuana Like Alcohol, referring to the chemical found in marijuana.

Currently, most drugged driving convictions are made based on police officers’ observations and then followed later by a blood test. There is not an easy way for officials to determine if someone is impaired by marijuana like the breath tests that are available for alcohol.

In Washington State, Coon explained that under the new law, officers will still have to see signs of compromised driving before pulling someone over, but that the driver’s blood would be drawn by a medical professional to test for marijuana use. If more than five nanograms of THC per milliliter of blood is found in a driver’s body, then that person would be convicted of DUI.

Some critics of the measure worry that setting these limits would make individuals who use marijuana for medicinal reasons fail the test even if they were not impaired.

Jon Fox, a DUI attorney in Washington State, said he is interested in challenging the state’s new guidelines as unconstitutional, since it hasn’t been scientifically proven how much marijuana would need to be in a person’s system to impair driving, the AP reported.

Colorado has not established any guidelines for driving standards and lawmakers are preparing to tackle the issue when they convene next year.