From what I remember, it was still a manual process.@Master Yoda do you happen to know if they are using an automated system for this? It wouldn't be difficult or that expensive to create an automated cleaning vehicle for the monorail that could run at night. If TDO were to consider the cost of labor verse the cost of an automated solution, certainly this would pay for itself in only a few years, if that long. That's assuming it cleans each beam only once per year.
Creating an automated machine is certainly possible, but often not as easy as it looks. There area myriad of issues that would need to be overcome (means are not a consistent depth, there is the electrical power rail, stations, etc) Automated cleaning also tends to be lower quality than manual cleaning. A street sweeper does a pretty good job, but if you want clean, a human has to come behind it.
Machines like that are also brutally expensive especially when you are flipping the R&D bill.
Odds are that manual cleaning currently produces better results at a more affordable cost.