At-rest position of the truck-tractor and Chevrolet. (Source: AZDPS with annotations by the NTSB.) Alt-text : On-scene, postcrash photo of the severely collision-damaged and burned-out remnants of the truck-tractor and the Chevrolet, seen from the right-side.

Multivehicle Collision Involving a Milk Tank Combination Vehicle and Stopped Traffic Queue

What Happened

On the evening of June 9, 2021, a truck-tractor in combination with a tank-trailer hauling milk, operated by Arizona Milk Transport (AMT), was traveling eastbound on SR-202 in Phoenix, Arizona, when it crashed into a queue of passenger vehicles that were stopped due to a road closure. The truck driver did not slow down or steer away as he approached the traffic queue at a speed of 62–64 mph. The combination vehicle struck and partially overrode the car at the end of the traffic queue, initiating a series of chain reaction collisions that involved six other passenger vehicles. Following the initial impacts, the combination vehicle crossed the eastbound travel lanes, struck the concrete median barrier and separated, and the truck-tractor and one passenger vehicle were consumed by fire. Four passenger vehicle occupants died and 11 occupants were injured; the truck driver was uninjured.

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What We Found

The video footage from the inward-facing camera of the commercial vehicle’s driver monitoring system showed the truck driver facing forward for 8 seconds before the crash but showed no visible indication that he was aware that the combination vehicle was rapidly approaching the fully conspicuous traffic queue. Based on this video footage, the truck driver was not distracted by an external source, and toxicology testing showed that he was not impaired. Based on the interview with the truck driver and the examination of his phone and work records, he had about 5.5–6 hours of sleep opportunity on the day of the crash.

AMT operated under a federal agricultural hours-of-service (HOS) exemption, which allows unlimited driving hours within a 150 air-mile radius. AMT’s safety culture was inadequate; the carrier had no fatigue management program that would have reduced the risk of fatigued operation by its drivers. Moreover, the carrier’s oversight of its drivers and enforcement of its own policies regarding the maximum daily and weekly on-duty hours was poor, as the crash-involved driver and several other examined drivers regularly violated those policies.

The federal HOS exemption is granted by statute for transportation of livestock and certain perishable commodities, including milk. Because motor carriers that operate under an agricultural HOS exemption are not required to inform the Federal Motor Carrier Safety Administration when using the exemption, the agency does not have a mechanism to identify those carriers or maintain information about their crash rate.

We also found that, as a result of the Arizona Department of Transportation (ADOT) classifying the road closure as a low-priority event as opposed to a high-priority event, dynamic message signs in the area of the crash displayed alternating messages regarding the road closure and dynamic travel time.

In addition, several of the passenger vehicle occupants in the Phoenix crash were not wearing or were improperly restrained by the available lap/shoulder belts, which increased their risk of ejection and exacerbated their injuries.

We determined that the probable cause of this multivehicle crash was the truck driver’s failure to respond to the fully conspicuous traffic queue, likely as the result of fatigue. Contributing to the crash was Arizona Milk Transport’s (1) poor oversight of its drivers, (2) lack of fatigue management program, and (3) failure to enforce its own policies, such as those regarding on-duty hours—all a consequence of its inadequate safety culture. Contributing to the severity of injuries to several passenger vehicle occupants was their lack of or improper lap/shoulder belt use.

What We Recommended

As a result of this investigation, we recommended that the US Department of Transportation (USDOT) develop and implement a program to determine the prevalence of for-hire motor carriers operating under agricultural HOS exemptions and study their safety performance, and to report the findings and any recommendations to improve safety to Congress. We further recommended that the USDOT require interstate motor carriers operating under an agricultural HOS exemption to implement a fatigue management program or, if necessary, seek congressional authority to do so.

We also recommended that ADOT revise its policies regarding dynamic message signs to classify single-direction road closures as high priority messages.

Further, we recommended that AMT implement an improved coaching program to improve driving behavior; implement a process to improve adherence to carrier policies, such as by verifying the accuracy of driver-reported duty hours and cross-referencing other information; and implement a fatigue management program.

To broaden industry awareness of this crash, its findings, and the risk of fatigue when operating beyond traditional HOS, we recommended that the International Dairy Food Association, the National Conference for Interstate Milk Shipments, and the International Milk Haulers Association inform their members about this crash and encourage motor carriers to establish a fatigue management program. We further recommended that the Commercial Vehicle Safety Alliance, in its promotion of the North American Fatigue Management Program, develop an outreach program focusing on motor carriers that operate under an agricultural HOS exemption.

We also reiterated several safety recommendations pertaining to implementing collision avoidance technologies and increasing the use of seat belts. First, we reiterated Safety Recommendation H-15-5 to the National Highway Traffic Safety Administration (NHTSA) to develop performance standards for forward collision avoidance systems in commercial vehicles. Also to NHTSA, we reiterated Safety Recommendations H 13 30 and -31 to develop performance standards and mandate connected vehicle technology on all new vehicles. Furthermore, we reiterated Safety Recommendation H-22-1 to the USDOT to develop a plan for nationwide deployment of connected vehicle technology, and Safety Recommendation H-22-6 to the Federal Communications Commission to protect communication between connected vehicle devices from harmful interference. We also changed the status of Safety Recommendations H-22-1 and -6 from Open—Await Response to Open—Unacceptable Response.

Finally, we reiterated Safety Recommendation H-15-42 to Arizona, the District of Columbia, and 37 other states to enact legislation that provides for primary enforcement of seat belt use law in all vehicles and all seating positions equipped with a restraint system.