Recently I came across a feature on a vehicle that caught my attention as an ergonomist. This was a new sport utility vehicle still on the showroom floor and I noticed something interesting in its design. The trunk has split doors. The bigger top door opens upwards like a traditional trunk and the smaller bottom door opens down similar to a tailgate on a truck. What struck my attention is the increased distance you are from the cargo in the trunk when the bottom door is down. When I tried reaching into the trunk my hands didn’t even reach half way into the cargo bay (see picture).
The split tailgate contradicts one of the most fundamental concepts of ergonomics: bring the work closer to the worker. When lowered, the bottom door places the human an additional 12″ further from the front edge of the trunk thereby increasing the reach distance between the worker and “the work”. Our design guidelines suggest that the maximum horizontal reach distance for infrequent lifts remains within 22″. With the tailgate down, the reach distance is well over the 22″ to just the middle of the cargo bay. Grabbing items from the back of the trunk would be extremely difficult with the bottom door down, but impossible without it down.
This can be a big challenge for an individual who uses the vehicle for delivery services requiring them to obtain cargo from the trunk often. In addition to the increased horizontal reach distance, the lowered tailgate causes soft tissue compression on the legs when leaning over to get cargo out of the trunk.
Obtaining the spare tire from the trunk poses another ergonomic risk. The weight of the spare tire (up to 90 lb for a full size spare) and the horizontal reach distance combine both high forces with awkward postures resulting in a high ergonomic risk. Whether you have an increased reach distance due to the tailgate down or having to lift the tire over the tailgate while it is in the up position, both positions increase the ergonomic risk.
Sometimes vehicle engineers and designers design for what looks good and do not keep the human body and its limitations in mind. Next time when you go grocery shopping or change your spare tire, consider the reach distances you encounter in your own personal vehicle. Are you extending your reach to retrieve items inside your trunk?