London Buses manages one of the largest urban bus networks in the world incorporating a fleet of 8,500 vehicles, 50 bus stations and 19,500 bus stops. Most bus services are run by private operators contracted to London Bus Services, which manages and monitors them to ensure service quality.
The service employs various wireless technologies including analogue radio to keep in contact with drivers, and its iBus system to track the whereabouts of vehicles and relay real-time information on bus arrival times to electronic signs at bus stops and to customers via SMS, the web, API (application programming interface) and apps.
The radio system is an MPT 1327 analogue trunked network supplied by Tait Communications. The network comprises 10 base station sites deployed around the M25, which provide 76 VHF radio channels, 10 of which are control channels.
Dr. Dimitris Kaltakis, lead radio infrastructure engineer, Technical Services Group, London Buses, says: ‘The VHF network is designed for the more powerful mobile radios installed in the buses. There is some hand-portable radio coverage, but it is not meant for it.’
The MPT 1327 system is used for voice control and emergency calls. Kaltakis explains that in an emergency situation the drivers press a Code Red button, which opens a channel to Centrecom – the London Buses command and control centre. Centrecom operators evaluate the situation and, if required, liaise with the Metropolitan Police, who are also located at the command and control centre.
A Code Blue button allows drivers to speak to Centrecom staff to report non-emergency issues. Controllers from each of the bus operators, such as Arriva, can track the whereabouts of each bus on an electronic display. By clicking on a particular bus icon, they can speak to the driver and issue commands. Drivers have a push-to-talk (PTT) footswitch to talk as they are not allowed to take their hands off the wheel.
‘The radio system is vital for bus operation,’ explains Kaltakis. ‘Operators have the authority to withdraw a bus from service if the radio system is not working – it is the most critical system we have to operate the buses.’
Radio pressure
But the radio network is under pressure. Kaltakis says it was designed to handle 30,000 calls per day, but current peak use is running at 65,000 calls a day. ‘We have close to 7,000 attempts to call buses in the peak hour which is usually between 8.45-9.45am – that’s a huge amount of traffic when you only have 66 channels available.
‘We are seeing strain on the system capacity wise, and being analogue it has problems with voice quality,’ continues Kaltakis. ‘We think it is the largest radio system for transportation in the world given the number of users – not necessarily in terms of channels, but for the amount of traffic generated.’
Unsurprisingly, London Buses is looking to upgrade the system, as David Fell, network architect, TfL, Technical Services Group, London Buses, explains. ‘There will be a 5-7% expansion of the network in the next few years, so that will really strain the system.
‘We are also going to increase the number of buses, as Crossrail will require more buses to deal with the extra number of passengers it will bring into London. The plan is to keep the same frequency of buses to meet increased passenger demand, so this will generate more traffic on the radio network.’
Fell says Transport for London (TfL), which oversees London Buses and London Underground, is waiting to see what solution the Home Office will choose for the UK’s new Emergency Services Network (ESN). This will replace the Airwave TETRA two-way radio network currently used by the three emergency services from 2016.
The Home Office has signalled a desire to switch to a 4G LTE cellular solution, potentially provided by a commercial mobile network operator.
However, that doesn’t mean TfL and London Buses in particular will switch to LTE immediately. Instead, the latter is contemplating moving to a digital PMR two-way radio solution as a stepping stone.
‘We need to find a cost effective way to expand capacity,’ explains Fell. ‘If we move to another PMR solution, potentially the DMR (digital mobile radio) two-way radio standard, then that provides us with an easier road map to upgrade the network.
‘But if we look at using LTE from a commercial operator that will cost considerably more and be more difficult to deploy. Another issue is that some of the key features we need, such as group calling, are not in the LTE standard yet.’
London Buses makes an average of 400 to 500 broadcast calls to the entire bus fleet each day. ‘At the moment, to do that using voice over LTE you’d have to establish an individual data pipe to each bus. That would be difficult to manage and very expensive,’ points out Fell.
Kaltakis says: ‘We would like to see a pan-TfL radio system for above ground, including hand-portables, especially when the Airwave network disappears, although that is only used in emergencies. But with contracts coming to an end maybe there is a chance to converge.’
Fell adds that Kaltakis undertook a study to determine when London Buses would need additional radio capacity in place and the answer looks like being at the back end of 2016. Hence, they have to start looking now for ways to do this, as the required EU public procurement route can take a while.
The iBus system
London Buses has 43 control centres controlling all the routes and it costs £1.6bn to run the bus network, so buses need to be tracked to ensure the system is delivering a good use of public money.
The real-time location data is therefore also used to measure operator contractual compliance with the service level agreements set by London Buses. The data provides an accurate record of each franchise operator’s performance, which can trigger release of bonus payments or fines if schedules are not met.
Other data stored on the bus computer includes the doors opening and closing, and deployment of the wheelchair ramp. Fell says: ‘If they haven’t operated the miles they were scheduled to run – and there might be a valid reason for not doing so, such as diversions – or something didn’t work on the bus that prevented it fulfilling its schedule, the data log files will reveal there was a valid reason.’
The buses are also fitted with an onboard 802.11a wireless LAN system operating in the 5GHz unlicensed band. After the bus has returned to its garage and the engines are switched off, the Wi-Fi is used to upload the log files to the garage server and to the London Buses central server.
Kaltakis adds: ‘It also has another purpose, as twice a month it is used to upload data for the latest scheduling. Normally that’s about 25Mb per bus, but if we add maps that can strain the wireless LAN.’
Trapeze’s iBus contract may be renewed for an additional five years up to 2020. ‘It is fit for purpose, it is not at capacity and it has a very low failure rate, so there is no business justification to upgrade it as yet,’ explains Kaltakis.
But when that time comes, it will mean replacing the main wireless systems on the buses. ‘This may provide the opportunity to look at a broadband solution then and see if we go for voice over LTE. But that is considerably more expensive to do than implementing DMR and if we are using a commercial mobile operator, that means we are not in control of the network,’ says Kaltakis.
Fell adds that should London Buses decide to go for a public LTE operator it could retain use of its PMR network as a fallback. ‘At the moment we fall back to an onboard GSM modem for voice, but we only use it in exceptional circumstances. At the moment, we have control of the system, so we can expand neighbouring sites to cover one site if it goes out. PMR systems are relatively simple and stable in that way.’
The current iBus system installed on all buses uses a combination of technologies including satellite tracking. The iBus system (originally from Siemens, now Trapeze) pinpoints the location of buses and relays information between the driver, garage and central control point.
The iBus system enables TfL to manage the performance of its bus operators, as well as communicate with traffic signals for bus priority, help to identify and monitor congestion and even deliver ‘low bridge’ driver alarms.
Kaltakis says: ‘The iBus core system became operational in 2007 and the last bus was fitted in 2009. The iBus radio system is used by Centrecom and by the bus operators, such as Arriva, for service control. Information on the whereabouts of buses is displayed on a route diagram.’
The diagram shows a linear view of stops and the direction of the individual buses. Each bus is colour coded: green means the bus is behind schedule; red signifies it is ahead; and yellow means it is on schedule.
Fell says: ‘As part of the real-time information system, iBus tracks the buses via their onboard computers, which use GPRS (2G) to send location data every 30 seconds – each transmission is only around 60 bytes.
‘GPS in London does not necessarily tell you where you are. It can be quite challenging in a multipath environment and the bus can be not quite where it seems to be. So other inputs are used to help correct the GPS, including gyroscopes, accelerometers, odometers and maps.
‘The information goes to the data centre,’ continues Fell, ‘and then feeds into the central computer system. Those AVL (automatic vehicle location) datagrams are the backbone of our passenger information system and of the service control, so the operators can see where their buses are.’
Countdown
The iBus system also provides prediction information which is used by Countdown, the system that provides live bus arrival information via electronic signs at bus stops (around 2,500 stops), web, SMS and API. On board the bus, all vehicles are fitted with audio syncs and visual displays to tell passengers where they are and what the next stop is.
The location information is fed through a predication mechanism to provide the Countdown bus stop information display signs as well as web, SMS and API/apps with bus arrival times based on the real-time traffic conditions and progress of each bus.
‘Finding’ a stationary bus stop is difficult, but vital if the bus arrival time information is to be of any use. Fell explains: ‘It is not based on schedule information. The real-time location information goes through a predication algorithm based on loads of journeys over time and calculates how long each bus will take to travel from this point to that bus stop.
‘It gets a measure of the previous bus’ journey and feeds that information into the system, so the next bus gets the most accurate estimate of the journey time to the next bus stop. The Countdown system provides very good accuracy.’
Wireless evolution
‘The system is evolving. We are trialling enhanced on board passenger displays, for example, so passengers can see their bus on the map. We are also trialling Wi-Fi for passengers,’ says Kaltakis.
Other ideas being trialled, as part of 2014’s Year of the Bus, include an occupancy solution, which would monitor whether seats are used on the upper deck. As passengers get on a bus they see a display showing spare seats on upper deck.
Looking ahead, London Buses wants to reduce the weight of onboard systems in the future. Fell explains: ‘When we do upgrade the buses, we would like to install a hub, a single gateway to the bus, which would house a Wi-Fi card, GSM card, PMR mobile radio card and other systems.
‘We want to provide the bus operators with onboard devices/modems in future, so they don’t have to install their own modems, as they do now. The risk though with a single hub is that you are then reliant on one piece of equipment.’
Summing up, Kaltakis says: ‘We are evaluating investment in a new PMR system and we are also trialling new wireless technologies and architecture with the aim to improve bus operations and provide diverse data and services that can be useful to the public and enrich the customers’ experience.’
Apps and Digital Signage
London Buses has also made available its bus location data to developers for free. The prediction data is made available via the Cloud to app developers. Developers can either take a pure data feed or use APIs to query London Buses’ interface.
The Digital Sign is the next step in London Buses’ Countdown programme for the provision of bus arrival information to passengers.
TfL’s Digital Signs are designed to enable organisations other than TfL to display bus arrival information to the public using their own display media, such as projection systems, TFT, plasma and computer display screens.
Digital Signs bring unique benefits that provide bus information away from the stop and can be combined with other information, such as other transport modes, weather or local information. Digital Signs work best in an indoor environment, such as hospital receptions, town halls and libraries and for commercially owned premises, such as shopping centres, supermarkets and entertainment venues.
Tfl has already signed up some important organisations, such as the Royal Marsden Hospital and IKEA.
‘We are trying to extend use of our data by getting it out there for free and let people make the best of it,’ says Fell.
Image source: Shutterstock/everything possible
