Jam-up and Obstacle

Jam-up noun - A crowded mass (as of cars) that impedes or blocks movement.

Obstacle and jam-up are semantically related. in obstruction topic. In some cases you can use "Obstacle" instead a noun phrase "Jam-up".

Obstacle noun - Something that makes movement or progress difficult.

Jam-up and obstacle are semantically related. You can use "Jam-up" instead a noun "Obstacle".