Little rain

Why is it that with a little rain the roads back up like there is no tomorrow? I heard on the radio that the travel time on the Monash freeway is 74 minutes! Its days like today that I am glad I take public transport. The train takes roughly the same time day in, day out... So why the vast majority of people choose to drive at peak hour is a mystery to me.
Another interesting thing I heard on the radio is that there are still millions of trips made every day on the roads that are under 1km. 1km is not that far to walk, when I was young, I walked about 1 km to school. Not only would walking more often solve the road problems, but it would help solve our nations obesity issues too.... So why not kill 2 birds with 1 stone?