The National Transportation Safety Board’s (NTSB) preliminary report on a fatal traffic incident that occurred earlier this month in Illinois doesn’t contain analysis or name a probable cause. It does, however, include a step-by-step breakdown of the complicated event which shows how varying speeds, sizes and positions of the vehicles involved affected the outcome.

The collision – or collisions – occurred on March 1 in Elmhurst, Illinois amid partially stopped traffic on Interstate 290. The roadway in this area has three travel lanes and paved shoulders in both directions of travel. A concrete barrier separates the eastbound and westbound lanes. The posted speed limit is 55 mph.