From Jeff Powers, who runs the Norton Rats bar/restaurant in Cusco:

"There is a stretch of road between Abancay and Cusco, about 40mi./60km. or so, which is extraordinarily slippery. It is slippery when dry, and worse when wet. I would say the asphalt was improperly mixed. I know of many bikers who have fallen along that stretch, including myself, even after warning other people. The road is the newest section between Nazca and Cusco, and looks great. You can see the bad part because it is blacker and shiny compared to the rest of the highway which is a grey rough finish, and gives very good traction."