Travelers often write in to ask a question I just hate: How long will it take me to get to the airport at this time on this date?

I hate it, because my first rule as your traffic doctor is to do no harm. And I can do a lot of harm if I give the wrong answer to that question. In the D.C. region, there’s so much traffic and so much road work that no two trips will be exactly alike, so giving a reliable time estimate on a long route is dicey.

When I do answer, I usually build in enough buffer time on my travel estimate that the questioner writes back and says, “I didn’t want to move to the airport. I just wanted to catch a flight.”

But I am going to try to answer this one from my online chats:

Getting to Dulles, 3 am, Nov 12

“I have to go to Dulles at the above date/time, and don’t currently live in the DC metro area. Will be staying w/family in Annandale, so plan to use the Beltway around to the toll road. Given the horrendous continuing construction and changes, what am I in for? Any advice on getting to Dulles w/out terrible problems?”

The traveler who asked this, starting with the chat of Oct. 24, may be from out of town but knows enough about the D.C. area to understand that the Capital Beltway in Northern Virginia is pretty much one big, long work zone. A lot of that work occurs overnight, to avoid the peak travel hours. On the west side, the work zones are mostly for the high-occupancy toll lanes project. Construction of the Dulles Metrorail line can also affect travel on the Dulles Access Highway.

Friday is Veterans Day, a federal holiday, and on some long weekends — Thanksgiving, for example — the Virginia Department of Transportation cancels road work to ease holiday travel. But this is not one of those weekends.

The other thing that typically interferes with the overnight road work schedule is bad weather. But the Capital Weather Gang’s forecast for Friday night looks pretty good at the moment.

VDOT’s schedule of Beltway lane closings looks fairly extensive.

For example, the schedule indicates there might be alternating lane closings on the inner loop between Route 29 and the Idylwood Road bridge from 9:30 Friday night to 7 a.m. Saturday. The ramp to the Dulles Toll Road may also be closed overnight Friday. A detour would take drivers north to Route 193, then bring them around to the outer loop and south to the toll road exit.

Of course, 3 a.m. on a Saturday in November is about as light as highway traffic is going to get, but the construction still adds an element of uncertainty.

So how about this as an alternative from Annandale? Take Route 236 (Little River Turnpike) west, continue on Route 50 west, then take Route 28 north to the airport. The trip should take about 40 minutes, but I’d allow an hour.

Do you see a flaw in this? Help me do no harm.