Buses hang over US highway
 

http://news.bbc.co.uk/1/hi/world/americas/7793109.stm

Unlucky it happened to them but lucky not to go over the edge.

The barriers seem totally inadequate to me . . .

The barriers are not that high.
No doubt they passed safety standards and were supplied by the lowest bidder but looking at the video again (near the end) it seems the barriers held and it was the road that broke away. Of course as soon as the barriers have no footing they become almost useless, they did appear to hold the other bus, probably travelling at a slower speed.

Now that's what I call driving on the edge.

I have always doubted the restraining qualities of bridge railings over here, just held by that bit of contact with the very edge of the concrete roadway.

I think good fortune has covered for poor engineering sense many times in the past.