It's not random, it's poorly engineered entrance and exit ramps. In order to maintain traffic flow, cars need to be able to increase to traffic speeds on on-ramps and decrease on off-ramps. Much have the beltway system put entrance and exit ramps where they definitely don't belong. Thoroughfares for in-city traffic also don't exist, the interstate has taken that role. To compound the problem, often times entrance and exit ramps are the same piece of pavement.