The bracket that hold the four LEDs used to monitor traffic between the Laptop (4), Raspberry Pi (3) and the Arduino (2) also houses the fan push-button control switch, a rocker switch to shut down or wakeup the Raspberry and a "Run" LED. The bracket formed from 1" square aluminum tube is mounted on top of the layout. 

Drawing for Traffic Monitor Bracket

Interface board to bring wires from the IOPi HAT, PWM HAT and the Raspberry Pi board together with some resistors.

Monitor IO Circuit

Monitor IO board. Black dots are all grounds.

Picture of Monitor IO Board

The monitor bracket houses (on the left) the fan push-button, 2 orange & 2 blue traffic monitoring LEDs, the RPi control switch and the green RPi ON LED. The RPi control switch is a momentary-on rocker switch, sleep in one direction and wakeup in the other with off in the middle. Shaping the ends may need a MIG welding unit.

Traffic Monitor/Switch Bracket