The current §397.17 rule requires drivers of vehicles transporting hazardous materials to examine each tire at the beginning of each trip AND each time the vehicle is parked. The old 100-mile-or-2-hour rule is obsolete. The Part 397 Cheat Sheet (downloadable) summarizes the current rule alongside §397.5 attendance, §397.7 parking, §397.13 smoking, §397.15 fueling, and §397.19 explosives instructions.