On Govt. ground a few new roads are actually built. In order to be able to build them, they are considered non-system or temporary roads and are torn up right after the logging is done. In a few rare cases, a temp road might be left open for firewood cutting, and then closed after that is done using $$ from the firewood program.
There are no plans drawn for temp roads. They are flagged in by the logging systems person or not, drawn on a map, and then walked and approved by the logger and or road builder and sale administrator. In olden times, any road over a 1/4 mile to be built was usually deemed a specified/system road and plans drawn up by engineers. That is no longer the case. There was one road that was about a mile long, and needed blasting and had a pretty severe grade to it meaning it had to be rocked in places. That rocking decision was made by the timber sale purchaser. Luckily, the rock from blasting could be used where needed.
Since most of the little bit of timber sold is on plantations, the roads are already in and are either opened up with a dozer or excavator. Most have merch sized timber growing in them if the road is in a unit so will be cut before the dozing or excavating.
I'd guess that 90% of the old roads have rock underneath the duff, and you will see us out there scraping with our feet to see what is under.
Logging used to take place year round. High elevations were done during the warmer weather and when snowed out, outfits would move to the lower elevations where it rained. Hence the need for rock and the use of yarders/high lead in the old days.
Sometimes the logger builds the roads and sometimes they contract it out to a road builder. That depends on the size of the logging outfit and the equipment and operators they have.
Above, a rocky spot that had to be drilled and shot. I got reamed for allowing that!
This guy could figure out complicated roads in his head and also had enough experience he could tell from the soil colors where he'd need rock or be likely to have problems.