How to transfer airport between Dulles Washington airport (IAD)to Ronald Reagan airport (DCA)?

Flight from Abu Dhabi will be arriving at IAD around 4.25pm on Thursday. Flight to DCA flying to Nashville is at 8pm. I read reviews and realised that the traffic is really bad.

I prefer non stop and shuttle bus since I never been to Washington.

Google it online instead of wild guesses here

A few options are debated. Non-Stop Supershuttle is a Shuttle Van with point to point service for US$60, no discounts. https://booking.supershuttle.com/

They make it $30 with stops along the way, not recommended. $29 with code 3JK26 and $27.10 with code SWMAG
https://www.retailmenot.com/view/supershuttle.com?c=9205404&redemptionChannel=online

Go Shuttle is an official transfer but low rated and is $59
https://www.theairportshuttle.com/airport_to_airport

In heavy traffic times, there's an express bus to a rail metro called Silver Line that then can transfer to the Blue Line.
http://www.flydulles.com/iad/silver-line-express-bus-metrorail-station
Takes about 1 hour 10minutes but difficult with luggage as walking in transfers.

There's also a public transport bus, the 5A that goes to the station for the Blue Line Metro. That is the cheapest method.

Washington Flyer Taxi estimates at $65 with no traffic, plus gratuities and could add tolls.
http://www.flydulles.com/iad/washington-flyer
You can taxi to the Silver Line or Blue line Metros.

Since everything is traffic dependent, no precise conclusion is made.
The Supershuttle airport to airport non-stop is probably the easiest and is reliable.

Wow - would love to know how that itinerary was booked!

Hopefully you will have gone thru USCBP pre clearance at AUH, otherwise you may be spending more time at IAD upon arrival than you would like. It's usually an hour to DCA but you are arriving at rush hour.

The nonstop Super Shuttle is going to be your best bet. A shared shuttle makes several stops, and while you may think that you have a lot of time, you do not. The Go Shuttle service generally requires that you have 5 hours between flights, which you do not.

There's also an option to take a bus to the Metro (subway) line, which goes to Reagan. That could be faster depending on time of day, and is definitely cheaper, but it might be more hassle with your luggage.

I assume you'll go through US Customs Preclearance in Abu Dhabi, which will save you some time upon landing at Dulles. But you will still have to wait for your luggage, and then get to the shuttle location. If you have to go through Customs upon landing, then you could find yourself at Dulles an hour or two longer, which would make it very hard to catch your flight at Reagan.