By Emily Woodbury & Ben Kieffer
Iowa Public Radio

It’s known that alcohol impairs the ability to drive, but what about marijuana?

On this River to River segment, Ben Kieffer talks with researchers at the National Advanced Driving Simulator (NADS) about a first-of-its-kind study showing how marijuana impacts a person's ability to drive.

They found that participants who consumed only alcohol weaved more than those who consumed only vaporized cannabis.

"We didn't see a lot of those lane departures that we see with alcohol," says lead researcher Tim Brown. Adding that, "We still see weaving within the lane."

Driving through simulated nighttime environments over a 45 minute period, the main difference between the drunk drivers and the high drivers was speed.

"[Drivers under influence of cannabis] tend to slow down," Brown says. "It may be similar to the effect you see with distracted drivers where they know that they're under some influence of impairment, so they slow down to buy themselves some time."

Also joining the conversation: Dr. Gary Gaffney, lead investigator and medical doctor for the study, and Andy Spurgin, an assistant research scientist at NADS. Trooper Josh Lewis of the Colorado State Patrol adds his perspective to the conversation as well, a couple years after Colorado's legalization of marijuana.

Later in the show, an explanation of a new report showing that Iowans bought 300 million addictive pills last year, and an Iowa mayor talks about his commitment to taking local action to combat climate change.

To listen to the entire show, go to http://iowapublicradio.org/post/driving-under-influence-cannabis-vs-alcohol#stream/0 and click on Listen.