When three or more people are riding in a car and they drive through a tunnel, all the windows are rolled down and everyone screams out the windows all the way through the tunnel. Their shrieking reverberates off the walls of the tunnel causing quite a ruckus.

when you're hungover as shit after a spending a night drunk as a skunk

Temporary, post 9/11 restriction imposed by the Port Authority of New York and New Jersey requiring all cars entering the Holland and Lincoln Tunnels during rush hour to have more than one occupant. This caused NYC-bound drivers to pull up to complete strangers at NJ bus stops and ask if they wanted a ride into the city. Sharing of tolls was optional.

When you are carpooling and you enter a dark tunnel and get that "uneasy feeling" as you sitting next to someone you don't "Really" know.

Repetitive-stress injury afflicting attendants at highway and tunnel tool booths.

A person who uses a car pool to travel to work, but is petrified to travel through an underground tunnel to get there

Any of a wide range of afflictions resulting from repetitive commuting. Most common are sciatica and butt zits.