A National Transportation Safety Board (NTSB) preliminary report on a fatal multi-vehicle accident in Boise, Idaho on June 16, 2018, shows how quickly things can spiral out of control in highway work zones.

Although the NTSB hasn’t named a probable cause for the incident, the timeline it has reconstructed shows that a truck driver’s failure to stop for traffic bottlenecked by road work led to a series of collisions and fires that killed four people, injured two others and damaged five vehicles.

The accident occurred on I-84, which was reduced from four lanes to one due to a maintenance project. The posted speed was reduced to 55 mph for the work zone, and a traffic queue had formed in one lane.

How it happened

According to the NTSB report, the driver of a 2019 Volvo truck-tractor in combination with a Great Dane refrigerated semitrailer “did not react to the stopped traffic” and crashed into the rear of a Jeep in the queue and collided with the rear of the Jeep Wrangler, pushing it into the rear of another tractor/trailer combination, which moved forward and struck the rear of a Ford Fusion. The Fusion slammed into the rear of a 2014 Ford F150, also sideswiping a 2015 Ford Escape. Debris from the collision also damaged a 2010 Ford Focus.

The vehicles came to rest on I-84 under the Cloverdale overpass. A post-crash fire consumed the Jeep and the 2003 and 2019 Volvo combination vehicles. The fire also damaged other vehicles and the overpass itself.

The toll

The driver and two passengers in the Jeep and the driver of the 2019 Volvo died, while the driver and passenger of the Ford Fusion and the driver of the Ford F150 were injured. The occupants of the other involved vehicles were uninjured.

According to data obtained from an aftermarket on-board Garmin unit, which recorded vehicle speed, interior audio, and forward-facing video when triggered, the 2019 Volvo was traveling approximately 62 mph at the time of impact with the Jeep. Additional data sources are being examined.

Truckers were exempt from Hours of Service rules

The NTSB is continuing to gather records on hours of service (HOS) and medical certification for the driver of the 2019 Volvo truck-tractor. Initial toxicology tests are pending. Preliminary information indicates that the drivers of both combination vehicles were operating under the agricultural products exemption to the HOS rules. Driver qualifications, HOS, use of electronic logging devices, and vehicle maintenance are being examined for both carriers. The NTSB is also evaluating commercial vehicle collision avoidance technology and highway work zone safety.

The agency says all aspects of the crash remain under investigation as it works toward determining the probable cause, with the intent of issuing safety recommendations to prevent similar crashes. The NTSB is working alongside the Idaho State Police, which is conducting a separate, parallel investigation. The following parties to the investigation are also assisting the NTSB: the Federal Motor Carrier Safety Administration, the Idaho Transportation Department, and the Penhall Company.