[desas]

It may be unlikely but it does happen. I know someone who drove off the road (60mph single carriageway) at high speed and into a bollard. The bollard went through the air, smashed through a house window and caused the inhabitant to have a heart attack.

[kanamekun]

If someone hits a pedestrian at even 40 mph, it's 85% likely to result in a fatality: http://www.streetsblog.org/2010/04/27/waiting-for-raymond-de...

If that same accident happens at 20 mph, there's only a 5% chance of a fatality. That's a big reason why London lowered the speed limit in the heart of the city to 20 mph: http://www.streetsblog.org/2013/09/13/the-heart-of-london-ad...

New York is pushing for a similar change... hopefully if and when it happens, more bollards can be put in place without endangering others. http://www.streetsblog.org/2013/05/16/neighborhoods-across-n...