A foolish question: Are you making a real traffic light for roads or a traffic light system just for small project?
There are Many MOSFET capable of handling 48V and above. E.g. - IRF740 capable of handling 400V Drain to source voltage and upto 10A of Current. It all depends on what is available to you. (It is available on the Tinytronics website of which you posted links in post#38.
I think you can use an external 9V PSU for powering the UNO, because 48V Buck converters are available but, I can't guarantee that if it can handle 48V or not.
Regards.