A transport company plans to fit all its trucks with devices that alert the driver whenever the vehicle drifts out of its lane, expecting this to cut the number of accidents. Which of the following, if true, most seriously questions the plan?

The device can only prevent the kind of accident it detects. If lane drift accounts for few of the company's accidents, fitting the device leaves the great majority of them untouched and the expected reduction will not materialise. Where the devices are made, driver unfamiliarity and fleet size do not bear on whether the device targets the real problem.