How sharp would you be after 28 hours without sleep? If your answer is "not very," you're like most people.

Doctors are like most people, too, once you take away the white coats, stethoscopes, and medical degrees -- but they're routinely scheduled for those infamous 28-hour shifts during their residencies.

Earlier this month, new rules kicked in that are supposed to limit shifts to 16 hours -- but don't celebrate this as a victory for common sense.

In reality, it's going to be business as usual at most hospitals.

Not only are 16-hour shifts ludicrously long on their own, but the new rules only require a five-hour nap at the end of them.

After that, young docs better stock up on coffee and Red Bull -- because they're back on the clock for yet another double shift.

Even worse, the rules only apply to first-year residents. In years two and beyond, those 28-hour shifts are still perfectly acceptable.

So much for change.

Now, a group of leading doctors and patient safety experts are calling for stricter limits, writing in the journal Nature and Science of Sleep that all residents should be limited to between 12 and 16 hours.

It's a common-sense approach that acknowledges the reality that some 180,000 patients are killed every year by medical mistakes -- and that many of those errors are committed by sleepy docs.

At one conference held last year, 26 experts agreed that humans simply can't function with a clear head after 16 straight hours of work. Other studies have found that lack of sleep can have the same effect on skills and judgment as a night of drinking.

And in other industries where public safety is on the line, there are strict limits in place. Truck drivers, for example, are only allowed to operate for 11 hours after 10 hours of rest.

Pilots are only allowed to fly for 12 hours in any 24-hour period.

But docs can keep right on slicing, zapping, diagnosing, and prescribing well beyond the established limits of human endurance.

And if that's not enough to keep you up at night, consider this: It would cost hospitals about $1.7 billion to hire enough doctors to allow everyone to get the sleep they need.

With that kind of money on the line, you can see why there's no rush to change the system.