Three months ago I reported on the state of the roads south from Phnom Penh to Kampot and Kep, recommending at the time taking an alternative route via Nation Route #2 (NR2) in lieu of the on-going road construction on the more direct National Route #3 (NR3.) Over the last few months the conditions on NR3 have improved greatly. Most of the construction on NR3 is now complete and the road is wide, flat and paved. A sure sign that NR3 is now the better route, most Kampot-bound taxis and buses have begun to use NR3 again instead of NR2. There are still comparatively short unfinished sections (a few kilometers) at both ends, near Phnom Penh and near Kampot, and several bridges are also still incomplete, requiring short detours. But the trip down NR3 to Kampot can now be made in about 3 hours, perhaps a bit longer, the same or faster than the alternative routes. As road construction seems to be moving along at a brisk pace and is in its final stages, my guess is that NR3 will 100% complete in the fairly near future.
Most direct route from Phnom Penh to Kampot: NR3 all the way.
Most direct rout from Phnom Penh to Kep: NR3 > R31 > R33 > R33a
See the map in my previous post.