Punched, spit on: Bus drivers regularly face violence on the job

On a sunny afternoon in February, a young man boarded the No. 13 bus at Castle Downs Transit Centre and got into an argument with the transit operator.
The man took offence after the driver pointed out he had boarded with an expired transfer. The situation seemed to cool off after another customer offered to pay for the man, who moved to the back of the bus. But when the driver called transit control to advise them of the issue, the man became aggressive.    
What came next is doc