Greetings -
As far as improvements, the crossovers have already been mentioned. I would look very closely at the turntable. I see a lot of long tracks off the turntable for long engines that would need to negotiate 36" curves to even get to the mainline. This could be improved easily. Also, your reversing loop to my thinking does not point in the correct direction. I would like to see a locomotive pull of the turntable, run around for a while, hit the reversing loop going forward, run around for a while longer, then finally pull forward onto the turntable to be turned around for the next run.
Below is a picture of the ruins of a small turntable by my house that only served to turn steam engines around at the end of the line.
