Passenger uses real-time vehicle data to show the location of a vehicle to passengers.
The majority of real-time systems in the UK use the SIRI (Service Interface for Real Time Information) standard for communicating real-time data.
Real-time vehicle data is sent to Passenger via a SIRI-VM (SIRI Vehicle Monitoring) feed - this is distinct from SIRI-SM (SIRI Stop Monitoring) which is used for departure boards, and may not even use the same supplier.
Passenger prefers to receive a direct source of data via SIRI feeds from the original data producer, this means that if there are any data issues it's easier to ascertain why and where in the pipeline these have been introduced. Therefore, making issues that arise easier to resolve.
Passenger prefers that where possible the same suppliers are used for SIRI-SM and SIRI-VM, as this reduces both complexity and the chances of inconsistent data between suppliers.