I think they only open it --other than during the wee hours --for
commercial traffic, and if you are there, you can scoot on thru. So
I've been told.

I believe that is so. But it happens on regular schedule 2 or 3 times
a week. I am sure the days can be predetermined.

I would not count on that. I've been on the way across the bridge
when it has been opened - on my way to catch a plane at DCA, and it
took them an hour to get the bridge back down - I almost missed my
plane. If it were to happen today, I'm sure we would miss the plane
as we did not check in until the gate was almost closed.

I'm not sure how your driving experience relates to the schedule of the
bridge?

But I believe the length of time to close was related to failing
mechanisms in the lift machinery. The bridge stuck several times over
the last 10 years.

I've lived in Alexandria and local region for 40 of my 50 years.
The bridge opens on schedule, as I referred above, for commercial
shipping. At least twice a week a freighter comes in to unload at the
Robinson terminal. There was much debate about that when the plans for
the replacement bridge were being considered. The new bridge will allow
the freighters to come through w/o having to open. Tall Ships will still
get the tip o' the road.