I was playing the scenario White Water Park (also known as Aqua Park), which starts off with a water slide, among other rides, already in place. I know water slides are among the rides that have to be carefully designed so that no guest is sent to an early grave thanks to a sharp turn, or by hitting a small incline at too great a speed!
During this playthrough, I made no attempt to change the water slide's track or operations in any way, and for two years it did not crash. On the third year however, one (and only one) of the dinghies crashed. The crash was far from the station and it exploded off-track, so it was not due to a brakes failure (if water slides can even suffer that particular breakdown). Of the guests remaining on the ride, they all completed the circuit and exited without issue.
From testing rides before, I know that trains with guests on-board can move slightly faster than those without, but the ride had been running with guests on-board for years without a problem. In cases of 'crashable' rides, is there always an element of probability involved in whether vehicles might crash under certain conditions? Is there anything outside of the ride and guests that can somehow alter the speed of a vehicle?
The crash occurred in the original PC version, with all official add-ons available.