Notice the use of "crush cushion" in connection with piers.

http://www.dot.state.fl.us/research-center/Completed_Proj/Su...
Article: “Vehicle Collision with Bridge Piers ”
The criteria in NCHRP-350 do not address head-on impact of barrier systems used to protect bridge piers. Such systems should not be confused with terminal crush cushions that are used to protect the ends of longitudinal barriers.

http://coldregionsresearch.tpub.com/CR98_07/CR98_070065.htm
a series of crush cushions can be developed for a range of pole or tree diameters…

http://www.freepatentsonline.com/EP1112412.html
Another aspect of the invention is a method of installing a crush cushion according to claim 7.
… Some of these devices and systems have been developed for use at narrow roadside hazards or obstacles such as at the end of a median barrier, end of a barrier extending along the edge of a roadway, large sign posts adjacent to a roadway, and bridge pillars or center piers . Such impact attenuation devices and energy absorbing systems are installed in an effort to minimize the extent of personal injury as well as damage to an impacting vehicle and any structure or equipment associated with the roadside hazard.

http://bimengineering.com/resources/1/IPE_Training_2010/2010...
Relocate Crush Cushion