They now want bosses to supply “spit kits” to collect the saliva of offenders for DNA testing.

The portable testing equipment will discourage the increasing number of spitting assaults on guards, station staff and drivers, the Rail Tram and Bus Union said. 

The union said spit kits, which have been a hit in the UK, allow rail workers to preserve saliva and hand it over to transport police for matching against existing DNA databases of people with criminal records. 

In the 12 months from April 2012 in Britain, 73 per cent of all spit kit submissions resulted in the DNA identification of an offender, helping track down and convict more than 400 offenders. 

This isn’t the only measure Sydney rail workers are requesting to protect them from violent attackers.

They also want Sydney Trains’ management to provide employee ID cards fitted with panic alarms and cameras to record confrontations with unruly customers.