Swiftly (version 1.17 and later) allows you to subscribe to alerts for any route. This is a very userful tool for those who ride the same bus or train every day, and would like push notifications when there's heavy delays or rerouting.
To subscribe to alerts:
At the bottom of the route's Arrival Times screen, select "Subscribe to Route Alerts". Be sure to enable notifications for Swiftly in your phone settings. When an official alert is issued, a pop-up notification will appear. As with any notification, you can customize how these alerts appear on your screen by adjusting your notification settings.