What is the significance of these numbers:
45, 100, 131, 132, 159, 171, 179, 197, 221, 505
UPDATE: It took a day, but two of you (plam and Kaycee) got it within minutes of each other: These are STM bus routes that end at a métro station and share the same name.
From contributor and transit geek Shanake Seneviratne:
The practice of placing a bus route's ultimate terminus on the destination sign is not one that has been adopted by the STM. Unlike other systems that indicate the endpoints of a route (Laval, Longueuil, Ottawa, and Toronto all do good jobs with their destination signs), Montreal has adopted a "dominant street or neighbourhood" naming policy. While this works well in principle, in actual fact this can backfire. The 168, for example, hasn't served Cité du Havre proper in decades. The 460 doesn't go on the Métropolitaine but rather parallel to it. The 215 is more deserving of the title Brunswick than the 208 is!
With new buses with excellent capabilities with regard to their destination sign, the STM can surely be more flexible and proactive.
Of course, most of these buses are actually named for the streets that the métro stations are named after, but there's an interesting debate on what names bus routes should take.
Maybe it's just because I'm so used to the Montreal system, but I tend to like it for the most part. It runs into trouble when routes don't take any particular street for very long. Naming buses for their destination assumes that people are going to that destination. While métro stations and terminuses are certainly big draws for transit users, they're not the destination for all.
Besides, with maps at most bus stops now, and the increasing use of smartphones to get information on the go, the importance of the name of a bus route has diminished.