This study was a multi center, randomized, double blind, active and placebo controlled, parallel group study to assess simulated driving performance in XP13512 treated subjects with Restless Legs Syndrome (RLS). Eligible subjects were randomized to receive a once daily dose of placebo (2 groups), XP13512 1200 mg, or XP13512 1800 mg for 16 days. On Day 16, one of the placebo groups also received one 50 mg dose of diphenhydramine (DPH) to assess the effects of an agent known to have sedative properties, while the other 3 groups received a DPH placebo.