Yeah, we have a ton of breaks every year. Im pretty sure it was a reinforced concrete pipe that failed. We replace Cast Iron Mains with Ductile Iron and now we're starting to do a thicker PVC 900 pipe. We have much older mains than that one that failed but you're right. The majority of breaks are from crazy temperature changes..... Sometimes there can be a fluctuation in pressure casuing an "air hammer" which blows them out as well.......
You gotta wonder how the heck we're gonna keep up with the old pipes breaking, and where do we start with such an important transmission pipe??
oh well, at least its job security for me..