The posters will be shown on all Cardiff buses

Drivers suffered 20 "spitting" assaults in 2004. On average, there has been one attack a fortnight over the last three years.

Cardiff Bus' Spit Bus-ters campaign follows similar measures introduced on trains in Wales six months ago.

If convicted, offenders can face six months in prison or a fine of up to �5,000.

DNA swab kits containing swabs, evidence bags and gloves for collecting saliva samples, will be handed out to Cardiff Bus staff for use in any spitting assault.

The kits are already in use in other areas of the UK, including by traffic wardens in one area of Scotland.

Evidence obtained using the kits can then be used by South Wales Police to help trace offenders through the national DNA database. If no immediate match is found, a record of the DNA will be stored and can be used in a future arrest.

This initiative will give us the tools we need to detect and convict people responsible for this anti-social behaviour South Wales Police Chief Inspector Andy Morgan

Cardiff Bus, Cardiff Council, South Wales Police, Crimestoppers Wales, British Transport Police and Arriva Trains Wales are all backing the initiative, believed to be the first of its kind for a Welsh bus company.

Deputy council leader Councillor Judith Woodman, who has responsibility for communities, housing and social justice, said the safety of both bus staff and passengers cannot be emphasised enough.

Chris Dexter, Cardiff Bus's associate director of operations said the launch, alongside investment in CCTV on all its vehicles was a clear statement of its commitment to staff and passenger safety.

"Any acts of violence, spitting or abuse will simply not be tolerated. Should anyone commit an offence, we will be able to identify them, publicly name them and seek to impose the maximum penalties".

Chief Inspector Andy Morgan from South Wales Police said the force had been working very closely with Cardiff Bus in recent months to reduce attacks on bus drivers in Cardiff .

'Safer place'

"This initiative will give us the tools we need to detect and convict people responsible for this anti-social behaviour.

"It certainly sends out a strong message to those who indulge in this kind of behaviour - it won't be tolerated and South Wales Police will prosecute those found responsible".

Chris Didio, head of safety for Arriva Trains Wales, said assaults against employees and passengers were "fairly rare" but one incident was too many.

"These swab kits have been successful in helping the British Transport Police to apprehend people who have assaulted our employees during the course of their duty.

"We are hopeful that the kits will act as a strong deterrent, minimise incidents of this nature and make Cardiff a safer place for all."