But the “number of overtakers” vs the percieved speed reduction isn’t linear, and hence neither is the risk or the average number of accidents.
We know that if lorries were all doing 300mph, not one person would need to overtake.
And if lorries were all doing 0mph, every one would have to overtake.
Between those extremes, a certain proportion of peoplpe will overtake.
If the average speed on a single carriageway road is say 50mph, a lorry doing 48mph would probably only be overtaken occasionally, but a lorry going just 8mph slower at 40mph would be overtaken a lot more.
And of course, it’s not just overtaking. If your in a queue behind a truck tomorrow i guarantee you’ll see terrible driving before anyone overtakes, with bunching, sudden braking, tailgating etc, all due to a lack of roadcraft on the following drivers.
Those who want to overtake, but can’t will get aggressive frustrated, those that don’t want to overtake will just switch off and “sheep” along, generally so close to the vehicle ahead they have zero visibility and hence zero pre-emption……