This answer (and the video link included within it) tells you all you need to know.
The long and the short of it is that good audio is essential to good video, and getting good audio requires its own set of techniques, practices, considerations, and, in many cases, gear.
Sound attenuates at a 1/(r^2) rate for point sources. Unfortunately, an automobile roaring through your walls functions more like a area source, not a point source, and thus decays very little from one end of the room to another. Nevertheless, a headset can put a microphone very close to your mouth, and that can push the room noise floor down fairly far. You might also consider making videos between the hours of 2AM and 4AM, when vehicular traffic is minimal.