I remember when this movie was first broadcast on the ABC Tuesday Movie of the Week - a 90 minute slot, so you basically had to produce a 75 minute or so movie. It was also out at a time when disaster movies were gearing up. Except for the junkie committing suicide, it worked well.
A lot of good movies were produced for that slot. Most notable: Steven Spielberg's "debut", "Duel". Also notable: "The Night Stalker" and "The Night Strangler", featuring Darren McGavin as reporter Carl Kolchak. The character was subsequently given a weekly series.
One other note: I believe there was an alternate version I saw on cable, where the disaster is given an explanation: A radical group planted a series of bombs at locations that caused the survivors to keep hitting dead ends. It detracted by adding unnecessary padding, and taking us from the survivor's point of view.