Why did the chicken cross the playground? To get to the other slide.

 
Alcatraz

Back in the 1940s, Alcatraz used to bring prisoners over by boat but it became really costly. So they started working on an underground system to transport people either by car escort instead. But, they realized that one path wasn’t enough, so the architects made a higher occupancy one.

After both were fully built, there was a ridiculously high number of car accidents only on the newer, high occupancy lane and nobody could figure it out. 

So they got other architects to inspect the work and brought in doctors to check if anything was wrong with the drivers. 

While the construction was fine, it was discovered that most of the drivers who crashed had horrible wrist and finger pain almost as soon as they went underground, leading to all the crashes.

Finally, one doctor figured out what happened. Carpool tunnel.