In a post apocalyptic world, people usually never go farther than 30 miles from whatever village or settlement they where born in. One of the exceptions to this is traders. Some trader have gone from one coast to another, and back again, multiple times. A trade company on North America plan on creating a way for trader to go from one coast to another. The problem is, many mutant creatures stalk the wasteland, along with mauraders m. How could they set up this trade network safely.
Set up fortified posts in each town on the route. Hire lots of mercenaries and send them with the traders from post to post in caravans that would make most mutants and marauders pause in fear.
Now fighting the entire way is bad for business, the use of ammunition, healing injured, replacing the dead, etc, all takes cash. So one thing the traders will want to do is find a way to pay off the marauders. The marauders need supplies as much as everyone, offer them nice discounts in trade as long as they don't attack the traders. In the wilder parts the traders could even hire the marauders to clear a path.
They'll have to crack heads first, and if anyone betrays them they must be wiped out as a warning for others. But doing it a few times will help ensure that people think twice before attacking the traders.
Now for the mutants, burn them out. Any survivors must learn to fear the sound of the caravan. Repeat this process until the trail is completely clear.
It will be a few decades before the trade route is really secure, so it's a long term project, but totally possible.
Do what the US did when it expanded west:
- Form an army. (Well, it already existed.)
- Set up a fort -- with integrated trading post -- just beyond your existing Safe Territory.
- Send out patrols from the fort to pacify the region. Be brutal, and cut off the mutants and brigands from their food and safety.
- Go to Step 2.
EDIT for clarification: be brutal against the brigands and mutants, not the villages along the way that are oppressed by the brigands and mutants.
Like Lewis and Clark did.
Lewis and Clark crossed the continent east to west largely over water, which offers a modicum of safety from mutants. It is easy to take rivers from the east coast to the Mississippi. From there you go up the Missouri, then hop the mountains to the Clearwater which turns to the Snake which turns to the Columbia which you ride to the Pacific.
The highland of the Rockies provide a little bit of a challenging portage. The company might want to improve and fortify this little bit. I imagine something like a crusader castle and maybe a series of locks. Also the travellers might be tired - from here it is downhill both ways and so people reaching this point have been coming upriver.