Originally Posted by Flaflyer

Since TSA never does risk management, I'll have to do it for them.

Suppose a couple of guys with white robes and beards travel from West Hideoutistan with a 155 mm shell and plan to place their IED under a US street. At home they plant their IEDs at night, as it is harder to spot them. Suppose in the US for some reason they plan to dig their hole in the daytime. They scout locations for a few days to find a rural road with a daily low traffic period to dig their hole.

School buses drive fixed days of the week, drive a fixed route, at the same time every day and driving the same direction, one way in the morning and one way in the afternoon. The IED diggers notice this and decide "no digging when the school bus is due by."

Schedule regularity means school buses are the most easily avoided vehicle there is, and thus school bus drivers are LESS likely to see suspicious activity than other forms of transportation. Duh.

OTOH, since no induvidual bus driver is likely to see a single "suspicious activity" in their entire lifetime, and that rare driver who does see a "suspicious activity" is lilely to only see one in their entire career, how are they supposed to notice PATTERNS? One or less than one event does not make a "pattern."