I bought a Garmin bike GPS computer in the fall and have been testing it every way I can. Its passed all my test even though there are some flaws but I can live with those for all the good things it will do.
I decided that next time I had to drive downtown in the morning I would track my drive and compare it to my bike commute although I take different routes for each method.
Even though my bike commute is 5kms longer it takes only 2 more minutes. Better yet, my average speed on the bike was 25.0kph (27.0kph moving) vs the car at 19.0kph (26.4 moving). I'm sure the 9 minutes (28% of the total drive time

) of sitting still in the car traffic had a lot to do with that and I have an easy drive through downtown.
Next time I do it I'll have to add my heart rate monitor to see how worked up I get stuck in traffic.
Full stats:
Bike - http://connect.garmin.com/activity/122812885Distance: 14.33 km
Time: 34:22
Avg Speed: 25.0 km/h
Calories: 665 C
Details
Timing
Time: 34:22
Moving Time: 31:52
Elapsed Time: 34:22Avg Speed: 25.0 km/h
Avg Moving: 27.0 km/h
Max Speed: 38.7 km/h
Car - http://connect.garmin.com/activity/132198528Distance: 10.24 km
Time: 32:22
Avg Speed: 19.0 km/h
Calories: 382 C
Details
Timing
Time: 32:22
Moving Time: 23:18
Elapsed Time: 32:22Avg Speed: 19.0 km/h
Avg Moving: 26.4 km/h
Max Speed: 64.8 km/h
Graph showing speed over time, bike is pink, car is blue.