hello, iam new and no native english speaker … but i missed a few basic modifications like:
Quater pipe with a door
an 4x4 [ half one of an 8x4 ] / 4x8 [ 8x4 vertical ] foundation [ placed on top of an quater pipe and or between a quater pipe and an inverted quater pipe ]
wall-like [ idl the wall skin [ or a wall with the foundation skin without any border-line] ] foundation [ 1x8? 1x4? 1x2? ] to snap on the edge of any foundation to build a way between on a 8x4 foundation or any other
quater-corner quater pipe inverted [ placed on the edge of a quater pipe line instead of an inner-corner quater pipe] + in addition foundations to build an curved areal like normal quater-corner quater pipe [ for an railway system ]
edit:
an underground train station … the half of the normal station with an side / front load system instead of the top load - perfect for a area like: quater pipe > inverted quater pipe > foundation 8x4 > tunnel > undergrond train station / system
more in the future 