The top of the line express train that ferries souls to the ninth underworld (The Land of Eternal Rest) in four minutes, saving them the four-year journey that it would otherwise take them on foot. But very few people qualify. Manny mentions that it's an available travel option "if you've led a really good life."
Those who had "saintly" lives are worthy of boarding the Number Nine and journeying to the Land of Eternal Rest in just four minutes. However, those who do not, either have to travel by cruise, by car or by foot with a walking stick with a compass in it, which means a four year journey for them. There are those who are evil and desperate enough to try to take the train using ill be gotten gains such as using fake or stolen tickets, however both the Gate Keeper and the train itself are not fooled by such tricks. Those who would do such a terrible deed are taken to the one place where they deserve to go: hell.