Oddly enough, there's no highway called "Blood Red Road" in Blood Red Road, though it would fit well enough with such locales as the Black Mountains and Darktrees. Instead, the title is an allusion to how much darn bloodshed our heroes encounter over the course of their travels, with a total body count reaching Grand Theft Auto-levels by the end. Yeah, it's bloody to say the least.
Pretty self-explanatory, really.