14-16 hours of wakefulness is where you start hitting levels of impairment that are equivalent to 0.04BAC, which is the DUI threshold for CDL drivers. Doesn't matter if you are driving, reading, etc.

Here's a link: http://www.businessinsider.com/chart-on-sleep-deprivation-20... There's a lot of public military research as well, but without the pretty charts.