A recent article on Jalopnik.com
states that Dr. Pete Snyder, VP of research at Rhode Island Hospital, authored the study named "The Effect of Acute Increase in Urge to Void on Cognitive Function in Healthy Adults."
Dr. Snyder said he didn't set out to look at the question of the effect of witholding the urge to urinate on driving, but in the end it was obvious there were some very real-world ramifications for it. He went on to explain that the urge to urinate is something that people have a hard time ignoring or distracting themselves away from. It's kind of like driving impaired or under the influence of alcohol.