CAUTION: STAY BACK 200 FEET. Not responsible for broken windshield.
What's wrong with this picture? As the driver of the vehicle stopped at a red light directly behind the featured truck, two things come to mind:
Error‐proofing, or mistake‐proofing, refers to the implementation of fail‐safe mechanisms to prevent errors from happening in the first place, rather than detecting them after they happen.
This activity is also known by the Japanese term poka‐yoke, from poka (inadvertent errors) and yokeru (to avoid). So, if the truck company is not going to control the process and adequately secure the payload, then they should at least effectively warn motorists of the potential problem.
How could this be done better in the observed example?
Taken to the point of absurdity, a flashing extra‐large warning sign could be coupled with an audible alarm on the rear of the truck. Both would be triggered by a motion detector that activates when a vehicle encroaches the 200‐feet space. More realistically, the abundant real estate on the truck's tailgate should simply be used to provide a visual aid that I can READ from 200 feet away.
The key to hazard warnings is to provide advance notice to provide the opportunity to avoid the problem, not to provide notification after encountering a dangerous situation. Do something that will make a difference, not just be a cursory cover for liability.
Never lose 'sight' of your intended reader.
Take a look around your workplace and check the visual controls, e.g. operating instructions, hazard warnings, Andon boards, etc. If something is intended to be a visual aid, then make sure that it's truly helping people where and when they need it. Most importantly, remember that any human detection scheme carries a potential for error.
What's that old adage about an 'ounce of prevention'? Be safe.
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