Final answer:
A characteristic of a highway corrosives tanker is the presence of external reinforcing rings, which provide structural integrity and durability for the safe transportation of corrosive materials.
Step-by-step explanation:
An identifying characteristic of a highway corrosives tanker is external reinforcing rings. These rings provide structural integrity to the tank, countering the effect of the hazardous materials and the potential for chemical corrosion over time. Unlike other tanks that might have heavy insulation or horseshoe-shaped cross-sections for other purposes, the corrosives tanker's design must ensure the safe and secure transportation of corrosive materials, and the external rings help achieve that by maintaining the tank's shape and durability.