Built more than 50 years ago, the Circle Interchange's high traffic volumes, single lane ramps and tight curves make it highly prone to delays and congestion, according to IDOT. Delays caused by the interchange average nearly 10 minutes a day per vehicle, for a combined 25 million hours annually. Most of the interchange's key components have not been improved since they were first built in the 1950s and 1960s, IDOT said.