Use Earth Colors Liquid Pigment(tm) to detail Culverts in your choice of colors. Approximate outside dimensions: 3/4"w x 1 1/4"d x 3/8"h About Terrain Structures Tunnel Portals, Retaining Walls, Culverts, and Roads reinforce natural terrain contours and add functionality, realism and interest to your layout. WARNING: CHOKING HAZARD - SMALL PARTS! NOT INTENDED FOR CHILDREN UNDER 3.