'Realityland' by David Koenig is an awesome book and has a really good section on the monorails.
"Ride operators had to train for 80 hours to drive the monorail, and the vehicles themselves were equipped with an artillery of saftey mechanisms."
"A two-way radio sysetm kept the driver in contact with the maintenance barn. If a tire went flat, the vehicles were to glide to a gentle stop. To prevent a runaway train, the pilot had to hold down a "deadman's switch;" if the button was released, the monorail slowed to a stop."
"Most importantly, an anti-collision system would stop the vehicles if they got too close to each other. "
However, this is not the first incident like this to happen. In 1974 a driver collided his empty Monorail Blue into Monorail Red (which was filled with 200 guests). This was in the Magic Kingdom station, and happened "before Monorail Red had a chance to leave." The driver had fatal injuries, and the train was only going 15 miles an hour. Obviously these trains aren't designed for impact for that slow speed to cause such catastrophe (unlike cars, for example).
Question is, how does that happen if the monorails are equipped with these saftey features?
Well, to the press the driver insisted that it was a brake failure, however, 'witnesses' heard him during his hospital stay talking about "overriding the automatic braking system". "He knew the locations of various switches and circuit breakers and how to gain normally locked electrical panels behind him. He also knew how the saftey circuits were wired. The kid was termed 'brilliant but bored.' He put a toothpick into a control console button to jam it into a held position while holding two controls with his hands. He removed a sock and shoe, twisted his leg back behind him into the electrical panel, and physically held a relay switch closed, thus defeating the wayside anti-collision signal commanding the train to stop as he drove past a red light into the train-ahead zone. He was a contortionist. He didn't realize the outiside of those monorails are made of Reynolds Wrap." These are words from the investigator for that particular case. According to Wikipedia, Reynolds Wrap has a thickness of "less than 0.2mm".
Post the incident, Disney got the two undamaged sides from the two trains, connected them together, painted the entire stirp blue and thus had a perfect monorail (to "minimize the press coverage"). The only other monorail collision to ever be reported at WDW was just after they opened, when maintance teams shut down the saftey system so monorails could get close together for an advertisement to be filmed. Unfortunately, the monorails ended up getting too close and "Monorails Blue and Yellow rolled into each other". Despite this just being a "roll", the entire front end of the monorails were destroyed. This surely shows how the thin chasis cannot cope with collision.
These are the only two incidents ever reported for monorail collisions, and they both have perfectly good explantations of why they happened. But none of them help us solve the issue of why this happened. I highly doubt the driver was attempting to overide the system at 2 in the mornign after July the 4th, with a (predictably) very busy train.
I feel so upset for the guy, it is such a terrible, terrible thing to happen. Fact is, it shouldn't have, and my money is on something causing the first ever failure to occur to the WDW monorail system. But what could impair Walt's flawless transportation system?