The bus operator says this scheme is a response to rising incidents of anti-social behaviour.
Passengers on Dublin Bus will notice some changes on their commute today.
A new security pilot scheme has been rolled out on some services.
The NBRU has long called for a dedicated public transport police to address the issue.
As of today - a pilot will run for 20 weeks which will see security guards on some routes.
They'll travel daily on afternoon, evening and night services.
Dublin Bus says incidents of anti-social behaviour have doubled over the past five years.
