Driving head on against a large truck seems pretty stupid, why did Humungus do that in Mad Max 2? What was he trying to accomplish?
From what I recall, Lord Humungus engaged his nitrous boosters in an effort to catch up to the oil tanker Max was driving. He hadn't realized that Max had turned the tanker around and was heading back towards him. You have to figure that his car was probably doing 140MPH or so with nitrous (heck, my old Pontiac Phoenix could hit 130MPH with its stock engine!), plus Max was probably doing 60 or 70 in the opposite direction. At those speeds, reaction time is almost nil.
Granted, it's a pretty flat landscape with little obstruction of view, but I think in theory it was an accident that the two collided.
Lord Humungus deliberately rammed into Mad Max head on, killing Wez and himself. I do not think he didn't know that Max was going the other direction, he would have saw him. The shot just before they hit shows Wez terrified whereas Lord Humungus accepting his fate. Adds to the chaos and the insanity of the wasteland and its occupants.
Max turned the trailer back, which Humungus didn't know, as he was far behind (which is the reason he used his 3xNitro injector: a hill blocked his view). By the time he realised the truck was in front of him his mask had already melted with Wez teeths...