I used to live in L.A. - and I've never seen it as bad
any freeway in rush hour there. I commuted to Portsmouth for a few years, and generally had no trouble leaving Madbury at 8.30 for a 9am start. However, any accident locks that place up far worse than usual.
Try this: head over to Google maps, and bring up the bridge. Type "traffic" in the search bar and hit enter. This will show live traffic. At the bottom of the page, change the option from "Live Traffic" to "Typical Traffic" and select a day and the time for your commute. Presto - traffic average speeds on that day and time!
More help here:
https://support.google.com/maps/answer/3093389?hl=en