They were at an intersection where a horse-drawn cart blocked the road and the view from a main road. Patton's driver became impatient and suddenly swerved around the cart, out into the path of the truck that hit them.
To say that this tragic accident seemed “staged” is somewhat moronic.
To correct a previous post; the movie is actually titled “The Last Days of Patton” and Patton died from an embolism while being prepared to be shipped back to the States in a full body cast.
It was known that Patton was dieing and they did not want one of America's greatest heroes to die on foreign soil, so they were preparing to ship him home to die in the USA.
(Google the history for yourself under the title I provided.)
Thank you for the additional info.
In the end, the embolisms are what killed him. Ironic ending to the career of a tough-as-shoe-leather old cavalry officer.