Comment by amiga386

So in the end it comes down to cost-benefit.

As Skytrain has no attendants, there's a certain level of risk of passenger injury and death no matter how good the sensors are. If Skytrain had platform doors, there would likely be less, but probably never zero, and TransLink baulk at the cost (for now).

Other systems, e.g. the Docklands Light Railway, which has attendants that can also drive if needed, are OK with paying those attendants (for now). I presume they've done a cost/benefit analysis and decided that it's cheaper to keep paying humans to ensure every train departs safely, and to operate the manual controls if the automation fails, than it is to upgrade the system to the point that doesn't require them and is also considered safe.