Traffic tie-up is a term used to describe a situation in which traffic flow is significantly reduced due to an obstruction or congestion. The most common causes of traffic tie-ups are bottlenecks, jams, and snarls. A BOTTLENECK is a point of congestion on a road or other transportation route that reduces the capacity of the route and causes delays. A JAM is a large group of vehicles that are unable to move due to the amount of traffic. A SNARL is a tangled mass of vehicles that are stuck in traffic. All three of these terms can be used to describe a traffic tie-up.