When police stop a suspected drunken driver, one of the first things they will do is conduct a series of three tests known as field sobriety tests. 

Police believe it’s a good indication of whether a driver is intoxicated.  

Critics claim the tests are designed for failure.

Target 11 Investigator Rick Earle went through a field sobriety test at the Pittsburgh Police Station in the West End. Sgt. Terrence Donnelly, a veteran DUI investigator, performed the tests on a sober Earle.

“I want you to follow it with your eyes,” said Donnelly as he moved a pen from side to side in front of Earle’s face. Earle followed the movement of the pen without any trouble. Donnelly said the eyes of an intoxicated driver will bounce or jerk as they try to follow the pen.

The next test was the walk and turn. Earle was instructed to take nine heel-to-toe steps, turn and take nine back. He completed that test with little trouble.

The third and most difficult test is known as the one-leg stand. 

Earle was supposed to stand on one leg and count to 30, but he began to sway and fell over at 13. 

“I've got to admit, to stand like that was difficult. I haven't had anything to drink and it was still difficult,” said Earle.

Dr. Cole Spurgeon, a retired Clemson University Professor who has studied field sobriety tests for years, contends they are flawed. 

“It's designed to fail. There are no norms. There is no average score. We have no idea what the average person could do on the one-leg and with the heel-to-toe. If you use all of them and do them right, you are only 26 percent better than chance, 74 percent as much error as you would be if you just randomly guessed,” said Cole.

To prove his point, Cole highlighted a study by the National Highway Traffic Safety Administration where police officers viewed field sobriety tests and then incorrectly identified 47 percent of the drivers as intoxicated.

We showed Spurgeon’s data and studies to Donnelly.

“From what I read about him, he has absolutely no idea what he's talking about,” said Donnelly, who’s been conducting field sobriety tests for more than 20 years and believes they are extremely reliable.

Donnelly countered Spurgeon’s argument by pointing to several other studies that suggest the tests are accurate and reliable indicators of intoxication. 

The tests, which are voluntary in Pennsylvania, are used by police officers all across the country. 

“Our average is probably close to 90. We tell people this is a whole totality of circumstances. It's not based on the way they were driving. It's not simply based on the way they were talking or the way they smelled. It's not just based on the field sobriety tests. It's based on everything as a whole. That's what leads you to believe that the person is impaired,” said Donnelly.

Donnelly told Earle if an officer determines a driver is drunk, the driver is then arrested and taken to the police station for either a breath or blood test to determine the driver's actual blood-alcohol content. 

Donnelly said occasionally drivers will blow or test under the legal limit, and in those cases, charges will not be filed against the driver.

Field sobriety tests are voluntary in Pennsylvania, but if you refuse, police can arrest you on the spot and take you in immediately for a blood or breath test.