Since we're speaking of design issues, one of my best junctions so far :
The idea was to create a junction without slowing downs at all: no up/down and at least 7 cases between two consecutive 45° turns. Problem: the throughput was not great, because some parts were under heavy use. So I added a couple of alternate routes. The result is above, and require a bit of explanation :
> going straight: red line, or alternate pink line if there's high traffic*
> turn right: blue line, or alternate aqua line
> turn left: green line
> U-turn: gray line (shoud avoid if possible, they make a large use of many parts of the junction, and there's a small slowdown near the center for longest trains)
* the opposite may be better, depending on the time lost with the down and up.
Now, I've to put some toughts into entry/exit pre-signals to improve the use of alternate routes under heavy use...
For a simpler design for small use, remove blue lines, pink lines, and the center square. It'll still work at fullspeed (except for U-turns), but it can slowdown trains under high traffic. If there's no penalty with close 45° turns, it can be done in a 10x10 square, maybe 11x11 or 12x12 to leave some room for more signals.