1 - traffic jams slow down public transit too if the road space is shared (buses, trams) or they increase the time needed to reach a train/subway station if you don't happen to live at walking distance from one.

2 - driving time is only half of the time you spend in a car. in Milan I could drive to work in 15-20 minutes, compared to 25-30 using the subway. good luck finding a parking spot though. they're either forbidden, very expensive or non existent. Not counting that many areas, like where my office is, are restricted traffic zones, getting a permit is really hard for non residents and fines are very high (very common in many medium to large cities in Italy). I gladly use the subway and read the news while commuting, so I don't even need to drive myself.

I'm really sorry for those that drive to work everyday, it must be hell, I don't understand how they can withstand it.