Along with amber and green!
Andrew Conroy has released a BBC BASIC library that allows Raspberry Pi users running RISC OS to develop software that controls the 4Tronix “Pi-Stop” traffic light board.
The Pi Stop is designed as an educational add-on that makes interfacing easy for beginners, and with Andrew’s library can be controlled from RISC OS. Up to six Pi-Stops can be controlled from the Pi at once, each connected to the GPIO pins in one of eight standard locations, leaving the remaining pins clear for other use, so they can be used either on their own or in conjunction with other hardware.
Andrew’s library can be downloaded either from his website, or via !Store.