Hi: I do a considerable amount of multi-mode commuting. My whole ride is about 19-20 miles each way (30-32 Km) and I do that a couple of times a week in good weather. During the winter, I tend to drive about halfway, park and ride somewhere between 8 and 12 miles. I also use the car if I need to get somewhere earlier in the evening, as it saves me about 20 minutes at the tail end of my ride if I drive 4-5 miles, and then ride about 14.

Invest in a good rack for the car, if you don't already have one. Consider security, in addition to ease of use, as you will eventually want to make a stop along the way home, and you don't want the bike disappearing from the car. I love my Saris Bones, but security is an issue - no easy way to secure the bike to the rack and the rack isn't secured to the car at all (there are ways, though).