I need to create an animation where the camera travels down a long 3d road that vanishes into a single perspective. What is the best way to approach this? The road needs to be very long (so the you don't see the end), and creating the road from a very long comp (around 30,000 pixels long!) creates errors when rendering.
there is a maximum layer size that you can hit doing this type of thing, but there are a few ways to get around it.
one way is to split the big layer into smaller pieces and then line them up. in your case, if you need a 30,000 px long layer, if you split it into ten 3,000 px layers then lined them up end to end, you'd probably be fine.
another way would be to find a way to fake it... an effect like corner pin could do basic perspective transform. offset could be used to have the texture move (if the road had a repeating texture or yellow line)... it would probably take further manipulation to get it to look right but it may be possible to do this completely 2d depending on what else is happening in the comp.
One trick I use for things like this is to animate a texture tile rather than the camera move on the road itself. I might try making a repeatable "road tile" then apply Offset followed by CC Repetile to it. Rotate it along the x axis it in 3d space, maybe do some extra distortion to make a true vanishing point, then animate the Offset Effect's value to make the road texture zip by. You could even apply effects like CC Bender on top of that to make your road appear to reach a curve.