Sounds like you live in an unfortunately car-centric location!

As to your original question: Yes, wide shoulders help. The main highway near me (the Trans-Canada) has a huge shoulder, and it feels pretty safe to ride on it. However, I tend to prefer less-travelled roads because of the noise. The sound of people passing you at highway speeds really starts to wear on you after a while.

If I have the choice between a low-volume narrow-shouldered road and a high-volume wide-shouldered road, I'd take the low-volume for long distances (touring) and the high-volume for shorter more aggressive training rides.