The train trip from the Noarlunga interchange takes 40 minutes to the city. I have friends who stay in Seaford and they drive to the park and go and commute in every day. The line is presently being extended to Seaford.
It's really quite difficult to put a time on the commute by car due to the "infamous southern expressway'! If you live in Port Noarlunga you will pick up the expressway at the top of Beach road...just a few minutes from the residential area BUT...it's reversible! It flows to the city on a morning and then changes direction at around mid day and then flows back to the southern suburbs. If you flow with the freeway the commuting time could be 20 minutes less than if you drive on South Road or Dyson Road.
The funding for the expressway to be upgraded to 4 lanes (2 in each direction) has been approved and work has begun so that will be sorted at long last.
Traffic here is not that heavy in comparison to Perth, Melbourne and Sydney and it's nothing like the traffic overseas. The Noarlunga to city line is presently being upgraded (there's lots of work going on in this city!) as Adelaide is the only capital city to be running diesel locomotives. It's all being replaced with electrification, new lines, engines and rolling stock so it should be a pleasant trip when completed. The central train station is served by a free tram network so if you don't have to drive in to the city...don't!