Regarding the reply from the TfL spokesman (No system failure for iBus, Letters blog, letters.computing.co.uk). The radios fitted to buses are either Band 111 or iBus, there is no such thing as a backup radio system. When the iBus radio is fitted to a bus the Band 111 one is taken out – the only backup the drivers have is their personal mobile phone.

With the Band 111, when the system fails at the garage the controller has no two-way contact with that bus or any other bus from that garage. But the driver can still call for emergency assistance by pushing the Code Red button on his radio.

If the iBus system fails at that garage, no one, including CentreComm – the central control station – has contact with that bus or any other bus. To reboot the system, every iBus workstation across the fleet, including CentreComm, has to log back on, hence the loss of emergency communication for those drivers. And unless they sort out that problem all 87 garages will have to log off and on once they have all been fitted out.

TFL needs to realise the main reason the radio is fitted to the bus. It is not just for controllers to contact the driver to control routes. The radios are there primarily to give drivers emergency assistance via a main London Buses control room, which is CentreComm.

If the bus has a defective radio and no Code Red facility, it is deemed unfit and does not go out on the road.

Name withheld on request