[Greenbuilding] suggestions for outdoor wall?

[Don Jennings]

A local non-profit charter school in my area is planning to enclose a 
grassy area as a place for kids to play. One of the concerns is that it 
is adjacent to a fairly busy street. Not surprisingly, they are 
considering a block/brick/concrete wall on one side for safety (i.e. to 
keep kids away from cars and cars away from kids).

Any suggestions for other materials or other ways to accomplish that 
goal which might be more environmentally friendly? We are currently 
investigating rammed earth (per MIT's rammed earth N51; see 
http://www.mit.edu/~jdahmen/rammed/ if you are interested), but didn't 
want to overlook other options.

Take care,
Don