I'm from Singapore. Here, every vehicle has an electronic device with a stored value card in it. On the way in, a wireless scanner logs you in, and on the way out the same system clocks you out, calculates the total time you spent in the lot (minus 5 minutes goodwill to allow you to find a spot) and deducts the appropriate amount from the card.
Both the entrance and exit are gated and the gates won't open if 1) all the lots are full or 2) you don't have enough value in your card to pay. Top up stations exist within walking distance so you never end up being unable to leave.
If my code's still running in 2100, our society has got way bigger problems than me not figuring leap years correctly.
You don't need your code to still be running in 2100 to reference dates in 2100. Simulation software, for one, might easily need those dates for predictions.