dr. dinges eluded to. the naturalistic driving study by the virginia tech transportation institute and in that study day instrumented 109 vehicles in the d.c. metro area mostly in northern virginia with in vehicle cameras and other data collection equipment and monitored these drivers 4 period of 12 to 13 months and with researchers many will be reviewing video from crashes and near crashes that occurred, looking at the signatures of drowsiness the doctor dinges noted in his presentation, the eyelids drooping, researchers were able to estimate the level of drowsiness of drivers and they estimated that 22 to 24% of the crashes and new crashes in this study involved moderate to severe driver drowsiness and again this was a study in the d.c. metro area where the bulk of the driving was done in circumstances that aren't typically associated with frequent drowsiness. next slide please. and other studies that took a totally different approach to this problem was a study by dr. jean stepson colleagues in the univ

dr. dinges. you talked about banking sleep, or recovery sleep. if a person is acutely sleep deprived, how much does it take for a person to sleep to pay that sleep back? if they have enough sleep, are they then safe to perform after that? >> thank you for the question. it's not as easy to answer as i would like it to be based on evidence. but the estimates -- we've been stud thing for the national institutes of helts and other agencies, as has other labs. it appears that the old belief that you can make it all up in one night is not supported by the evidence. that belief came about by only allowing one night of sleep, and people looked fine the next day. so they let them go home. when you keep them in the laboratory and you study how they function, how safe they are, you realize that in fact it takes more nights of steady sleep to get you back -- of longer sleep. it would be vastly better to not get sleep deprived than to attempt to recover from it. and i realize that's a harsh message for the public that has gotten used to sleep deprivation. but