Dirt slabs (a road with no directional arrows) will raise and flatten the terrain to the highest corner of the square it is built upon. Caution should be used when placing dirt slabs on steep inclines, as it will raise the surrounding area - including the area under buildings or neighboring dirt slabs.
Placement: Use the arrow keys to change road facing directions, press - to remove all arrow facings (slab), mousewheel down while cursored over an existing road to copy the road facing, and mousewheel up to invert the current facing (left-right becomes up-down).
Roads in general require one labor to build, but slabs take additional labor to level the ground and you cannot demolish a road until that labor is done. Roads can be placed next to unfinished roads.