The study authors, Dr Murray Mittleman and colleagues at the Beth Israel Deaconess Medical Center in Boston, measured kidney function using a recognised test called the glomerular filtration rate (GFR).
Which ever department was considering a policy change would carve out a group of 20 to 200 drivers, make them function as a separate business and test the results.
Many schools and sports medicine programs offer tests to athletes before they start contact sports to measure their cognitive function, which can then be compared with the same test administered after a concussion.
While the jury's still out on Jacksonville's marriage test, there's little debate that meeting a player's wife serves another important function: "She's usually a big part of the decision-making process, " Smith said.