Social traps are negative situations where people get caught in a direction or relationship that later proves to be unpleasant, with no easy way to back out of or avoid. The concept was orignally introduced by John Platt who applied psychology to Garrett Hardin's "Tragedy of the Commons", where in New England herd owners could let their cattle graze in the common ground. This situation seems like a good idea, but an individual could have an advantage. If they owned more cows, the larger herds would deplete the grass, and excessive herds and overgrazing can destroy the field and result in a collective loss for everyone (Hardin, 1968). Platt recognized that people who operated on short-term gains had a tendency to exploit resouirces, which led to long-term losses for society.
Applications
In addition to congested highways, you might know someone who's purchased a gas-guzzler when the price of gas became low due to high supply. What happens when more people do the same, fueling their vehicles with more gas, which in turn depletes the supply? The same pattern can be found in the way people think about environmental contamination. For instance, one farmer uses pesticides to get rid of a few pests. He thinks no one will even notice, but then his neighbors do the same thing, and over time, they collectively cause damage to the town's water supply.