Use Google maps or other programs to explore alternative routes. Don't look for the shortest, fastest route but the safest one. If it's a little longer, that's more miles of training. I told myself for years that my commute route was too dangerous for cycling, until I started actually studying some maps and exploring alternative routes. I found several routes that are 2-3 miles longer than my driving commute, but have much less traffic and generally safer roads. I also invested in a good light system (head and tail lights) and some bright jerseys so I am very visible in traffic. Now I can't believe I wasted so many years driving when I could have been bike commuting.