A simple spit test could soon help police officers keep tired drivers off the road. Sleep researcher Paul Shaw and his team at the Washington University School of Medicine have discovered that amylase, an enzyme in saliva, correlates to sleepiness. The scientists observed high levels of amylase in volunteers deprived of sleep for more than 28 hours but found that levels normalized after a good night's rest. Shaw says it could take a few years to pinpoint the markers in saliva necessary to develop an accurate field test. Until then, rest up-drowsy drivers cause roughly 100,000 accidents in the U.S. every year.