ScreamRide

I was able to get this pretty easily after playing the game randomly a little bit. So I started with this achievement at 61%. I initially tried popping this using sandbox, but after building and saving at least 10 sandbox levels with very long tracks (some with just under 5,000M), my percentage did not move up from 61%, so I decided to try some actual Career levels. I started with Series 1: Engineer level 1 (Behemoth) and built as much track as I could, ran a test and exited and my percentage was up to 67%. I decided 6% (67% - 61%) at a time was going to take forever to complete this, so I moved on to Series 1: Engineer level 4 (Substation), which has up to 1,200M of track to place. I started laying as much track as I could while still being able to autocomplete the track to finish, so that I could at least run a test run, and after doing a test run and exiting the level, I was at 84%. So I did this one more time and was up to 94%. A whole 10% gain on that level was promising. So I did this level (Engineer level 4 (Substation)) one more time and popped this achieve. I'm not sure if you have to test each level for the track to count, but I did so just in case, and got it eventually.
I think the main takeaway here is that Sandbox doesn't look to increase the percentage on this one (maybe I needed to test the sandbox levels?).