Soundproofing a room from outside traffic noise and vibrations
With difficulty. If you really mean "soundproof", you're essentially talking about the equivalent of building a sound studio, so I'd suggest websearching for discussions of building a home studio to learn the tricks and techniques. Depending on exactly how much sound you need to block, at what frequencies, there are different techniques. Don't forget floor and ceiling as possible paths, especially for low frequencies.

Discussed some of this with a friend who was building a fairly serious studio. Walls with offset studs (drywall on each side attaches only to every other stud, never both to the same stud) so there isn't a direct mechanical path from outside to inside; that cuts down bass leakage. Fill those walls with sand (yes, that's a lot of weight, and a maintenance hassle should you ever have to do anything to those walls; this was in his basement) to cut down treble leakage. Install an acoustic ceiling, suspended from elastic fittings, to reduce noise coming from above. (Which required that he increase headroom, which required that he sister joists with iron C-beam so he could cut back the wood and gain a few inches.) I think he had some specific design for the floor as well, but I don't remember what the plan was there.

Even so, he was mostly planning on recording at hours when there was minimal traffic in the area, and (I believe) he was assuming he'd have to turn off his heating system while recording to keep its noise from coming through.

And he didn't have to worry about windows. Or the door, since the studio door would open to the control room which was similarly soundproofed and would provide some isolation.

If you're willing to settle for just reducing the noise, there are less expensive things you can do.