Those front discharge mixers were invented right here in Utah in the early 70's.
Story is, they wanted a more efficient way to transport the mud for one specific job-the placing of the footings and foundation for the smoke stack at the Kennecott copper mine smelter:
http://en.wikipedia.org/wiki/Kennecott_Smokestack
Invented by a fellow named Royal W Sims of Holladay, Utah:
http://en.wikipedia.org/wiki/Concrete_mixer
I don't think I've seen a rear-discharge mixer in Utah in 20 years. I don't know why everywhere don't have these FDM's. I have heard that some unions won't let them in because they may eliminate the chute-mans job, but the logic of that argument escapes me. I have never been on a flatwork crew that wasn't shorthanded. The chute man don't lose his job-he just loses his easy Job
Besides, the newer rear-discharge mixers are completely remote controlled, with the driver controlling the chutes and even the truck itself from outside of the truck via a wireless controller. They have some of those up in Rock Springs, Wyoming, where my current job is. They're pretty wild!