ADD: noise barrier based on gauthier's "palissade" fence

James,
this is the wooden palisade fence repackaged as a noise barrier. The .dat file needs calibration (I think cost and maintenance are approximately right, but the introduction year of 1968 is probably far too late), but for testing things this should work.

One problem with moving the fences to the edge of their tile is that four-way intersections have no visible indication of whether they have a noise barrier. That could be changed if we were to move the fences a little towards the centre of the tile, but that requires adjusting the base image quite a bit, and at some point it would probably be faster to use Blender.

Philip