I can't tell for sure by the pics, but it looks really similar in size to what we use..and what Stockton R/C uses..and Bending Corners uses...and a few other tracks I've been to.
We use 3x3 PVC "RainGutter DOWNSPOUT" It's perfectly square tubing 3x3" x 10'
I was able to find a different brand that is the OUTSIDE diameter...or what the 3x3 INSIDE diameter is...and I cut it in 1' lengths to join the pieces together cleanly.
The 10 ft. lengths were about 8 bucks each if I remember correctly..and they came from the local "Orchard Supply Hardware" store.