I am planning a TransAmerica Self-supported bike tour with my wife in 2016. Which direction is optimal and why? We will do the middle of the country Adventure Cycling Route- I believe Astoria and Virginia Beach?!
There are quite a few possible factors to consider, but to me the most important are weather and which end is closest to home.
Wrt weather and direction of travel, basically if you go early in the season start in the east and avoid the heat and humidity there and the snow in the Rockies. If you go later in the season starting in the west works well.
If you live near one end or the other, my preference is to fly to the far coast to start. It is easy to know when you will start a tour, but knowing when you will finish is another matter. That makes it easier to plan air travel for the start. Also it is nice to have friends and family to meet at the end.
People often mention wind as a factor and suggest riding W-E because of the supposed prevailing westerlies. That would make sense if you were traveling at 30,000' of altitude. I wouldn't choose direction of travel for the TA based on the winds, but if I did I'd go east to west. In the middle of the country the Trans America angles southeast and the surface winds in the Great Plains tend to be out of the SE in summer.