After reading other threads on transportation between the two airports, I will book a car/shuttle to transport 3 of us between airports.

My concern is the time needed to get from IAD to DCA on a Sat. early afternoon. Right now, we have a flight arriving from LHR to IAD at 12:50. I'm looking at booking DCA to ORD at 4:00pm. Does that time sound feasible considering retrieving luggage and traffic? Thanks for any input.

The obvious question is why are you not booking LHR-ORD? Or LHR-IAD-ORD?
That said, assuming your inbound TATL is on-time, assume an hour to get through immigration and customs and collect your bags. Traffic on a Saturday afternoon shouldn't be so bad ... 30-40 mins to DCA ... that gets your there in just about enough time to queue and check-in again? The 3 hours 10 min doesn't leave a lot of wiggle room, and if your inbound is delayed, you really will be at the mercy of the carrier of DCA. Do you have any airline status or would you be travelling First or Business? That may help a little. Also, flights from DCA-ORD go approx once an hour. Could you book a 5pm to be safer?

I would not do this without Global Entry and airline status.

- Between summer peak travel season and the sequester you could easily have significant delays at customs. You also have to factor in the annoying moon buggy ride to the international arrivals area and any delays at baggage claim. I would not plan on being out of the airport before 1:30 even with GE. Figure 2pm without GE and it could easily be longer.

- I-66 is often congested on Saturday afternoons in summer, especially if it's a nice day or there is any type of event happening in DC. So you could easily end up at DCA with less than an hour to spare. And..

- TSA lines can be problematic at DCA - status will help you here.

Believe me, I would love to to book an alternative to changing airports. The combination of short planning time, and semi-newbishness with reward bookings beyond anything straightforward leaves me with limited options. I get that, and I'm not complaining, it's still a nice family trip with a lot less out of pocket than I'd normally pay.
The bookings (which are on hold for 1 more day) are actually FCO-LHR, overnight, then to IAD (both on BA, so...fees!), with AA Gold status (my son's). Then: DCA-ORD is on United, no status. I know...not great, but late to book.

Thank you for the good advice. It seems wise to head back to the drawing board and hope for better options. If necessary, I guess we could just spend a day in D.C., a place I do love, but we'd much rather just get home at that point.

I'm surprised that UA has better fares on DCA-ORD than IAD-ORD. Is the DCA-ORD on an RJ?

why would an rjp change the rate? the md80's or whatever they are called are horrible planes.

last sat, we had a beautiful day in DC. i had to take my dog to the vet. traffic at mid day was similar to a 4pm friday rush hour. no games, high gas prices, and everybody was out shopping. this crowd was not the normal gunning commuters, but a lot of housewifes out shopping. the whole thing was much worse than rush hour.

i would recommend listening to wtop traffic when going. there is a lot of construction on the dulles airport access road(or whatever you want to call it). the new silver line is going in.

the silver line construction is getting close to the reston parkway. looks to me like it is on schedule

DCA-ORD is almost all mainline. Usually a combo of 319, 320, 73x, and 752. I think the 6am on weekdays in an E70. Service is pretty much hourly.

As for the OP's question, there's no way I would chance only 3 hours when clearing customs and dealing with NoVa traffic.

The moon buggy is irrelevant. It only takes marginally longer than the walk through many large airports most of the time. The sequester, however, could be a major problem. My last trip through IAD had major sequester delays at both immigration and customs. Sequester delays added more than 30 minutes to my standard deplane to curb time.

I would assume that with arrival at 12:50, even 2pm is a stretch, probably more like 2:30. That is not enough time to make a 4pm flight at DCA unless road conditions are perfect, which they are unlikely to be.

Just want to thank everyone for the input. Glad I asked.
I'm going to book something out of IAD and not deal with changing airports.

what's wrong with moon buggies??? they have the same things at cdg? at muc, vie, fra, zhr, geneva, almost every italian airport, they put one on a bus, drive out to nowhere, and then climb a 25-30 step ramp with carryon to get into the plane. no cover from rain and snow. stod in the rain in vie, while they tarmac checked my luggage. no receipt. just a pleasant "get on the plane" i never hear anyone complain about those bus drives

at the beloved dca, the ramps are stored out in the elements. if it snows, the ramp is ice covered.