In reality, it was two backups that merged into one epic traffic jam.
Initially, one lane of southbound US-131 was blocked around Hall Street, and traffic backed up into the S-Curve in short order.
Meanwhile, southbound traffic was becoming heavy at US-131 and Ann Street. When that happens, traffic backs up as far as Post Drive as well as on eastbound I-96 from drivers trying to merge onto southbound US-131.
The backup caused by the Hall Street accident got to the point where the two traffic jams met at Ann Street, which meant traffic was at a crawl for several miles beginning at Post Drive north of Grand Rapids.
The crash near Hall Street was finally cleared around 8:30 a.m., but it took quite a while for the traffic jam to dissipate.