Communication systems in public transportation

This article concentrates on the relations of a complex information system for public transportation, the ways how these systems can be interconnected (dispatching, depots, stops, passengers and transportation route technologies) and describing individual types of communication and technology.

The past and the future of communication in public transportation

The goal of this article is to show the very complex relations of public transportation control systems and informing passengers about the current transportation situation.  This topic also includes passenger checking systems, transportation route control and advertisements in vehicles and on stops. Although some systems are „wannabe independent“ they use similar communication ways and protocols. This is the reason why it is necessary to talk about complex information systems and to build these systems universally using various communication routes.

Island Systems up to 2000

In the Czech Republic, the first public transportation vehicle communication systems (I. Generation systems) appeared in the middle of the 1990’s. They had a simple structure based on slow IBIS busbar (a German standard from the 1970’s, its speed was 1200 bit/s). Basically this system provided inner and outer information tableau setting.

Basic features of an „island system“:

• On-board computer
• Outer information panels (optic tableaus)
• Inner information panels (optic tableaus)
• Multiple digital stop and other announcement annunciator, acoustic switchboard
• Optic display of tariff zones and time (time and tariff indicator)
• Ticket markers (checking system)
• Signal receivers for vision impaired people getting on and off the vehicle (first outer radio communication)
• Tachograph (just records data from on-board informatics)
• Radio station (independent control – outside of the IBIS busbar and on-board computer)

Fast busbars and dispatching control

Another step in changing communication systems came after 2000 when the „fast RS 485 busbar“ appeared. Its communication speed of 115 kbit/s and its reliability made it possible for new functions to be integrated – above all connecting outer vehicle radio communication (voice and data) which included not only  communication with a central dispatching but also communication used in depots for the purpose of data updating. It also started to be used by the developing checking systems.

80 – 200 kbit/s radio communication started to be used to update vehicle data in depots and special communication protocols were developed for this. The power supply of these systems also changed. The systems were connected to a permanent power supply and vehicles were therefore able to automatically change  tableau and digital annunciator data while in a depot.¨

Utilization of computer technology

Utilizing computer technology and networks in public transportation vehicles was another important change (III. Generation systems). This important change started in 2009 and it brought:

• On-board computers containing PC computers and thus also higher programming languages including operating systems, i.e. SW development sped up.
• Standard way of routing in computer networks and the necessity of using firewalls and intelligent routers. It is necessary to separate the vehicle internal computer network from the update WIFI and from the data coming via a GSM network (at that time only GPRS, later UMTS (3G)).
• New way of vehicle updating based on depot WIFI networks – in comparison with the previous ways about 100 times higher transfer speed and the possibility of updating anytime while the vehicle is in a depot.
• Fast transfers of large amounts of data inside vehicles from/to components that need it – mainly vehicle LCDs tachographs and checking.
• Possibility of transferring on-line data via mobile operator networks.
• Integration of a number of previously independent units into one on-board computer (e.g. intelligent power supply units, digital annunciators, GPS units, on-board computer, memory media, etc.)
• Utilization of universal radio stations capable of voice and data communication with dispatching
• Utilization of the IBIS busbar has remained the same as in previous years and the fast RS 485 busbar is rather used for technological control or communication between joined trams.

Current vehicle communication arrangement

The present (IV. Generation systems) is characterized by widely accessible public internet spread mainly by mobile operators using 4G networks, i.e. LTE (Long-Term Evolution) designed for high-speed the wireless technology of cell phones and data terminals.  As per the LTE standard a communication links to a vehicle can reach 300 Mbit/s (download) and sending data out of a vehicle up to 75 Mbit/s (upload). Communication is also possible for fast moving vehicles and group data currents are supported.

LTE modems are already available in an industrial rendering. LTE is widespread and affordable in cities. That is the reason why the view of vehicle infrastructure is changing and new solutions of vehicle data infrastructure are appearing that would be impossible a few years ago (see pic. no. 4).

IV. Generation of these systems includes the following changes:

1. Two new vehicle Ethernet networks:

• Vehicle camera system network (Ethernet_3) – is given by the connection and integration of a vehicle security camera system to an on-board computer. The camera system is equipped with independent control and recording. The number of cameras connected to the system of a multi-joint tram can reach 20.
• Network for connecting a public WIFI (Ethernet_4) – makes it possible for passengers to connect to public internet.
• As for performance and security these two networks should be separated by a router from the basic vehicle on-board network for the checking and information system.

2. The network contains specific routing rules that can be used to interconnect individual networks. In that case the communication unit contains at least 4 independent routing rules:

• Routing and communication directed to the on-board checking and information system (routing rule no. 1) means online transfers of information about checking progress or transfers of traffic information to the driver or passengers.
• Routing and communication directed to the security camera system (routing rule no. 2) means that it is possible to transfer camera data currents to the dispatching (video call) or to the police, it is also possible to download critical sections on demand.
• Public internet in vehicles (routing rule no. 3) means routing customer requests to public internet and receiving data from it. Because of data tariffs it is advisable to restrict access to servers where video files can be „downloaded“.
• Public advertisements in vehicles (routing rule no. 4) – there is an independent advertisement LCD in a vehicle that displays advertisements, general news, short videos, etc.

Picture no. 4 depicts a known possible vehicle system arrangement and it clearly shows that such a vehicle arrangement requires skilled IT technicians to take care of data preparation, maintenance and service. This arrangement is not unequivocal, there already is a number of various arrangements based on the needs and historical development of transportation companies. Picture no. 4 therefore shows one of the possible overall solutions.

Future of the system

The development shown by the pictures clearly indicates IT technology integration has become a common part of vehicles and it has been progressing very quickly. At the moment it is necessary to work on integration in the field of ITS (intelligent transportation system). These systems are in the research and development stage at the moment and people all around the world are intensively working on their development.

This means that a new conception of vehicle system installation and communication can be expected in 2019. These systems will be V. Generation systems. They will be equipped with another type of communication – this time with transportation infrastructure. Individually, this communication is already utilized today e.g. radio communication providing public transportation preference at intersections. However, this has not been converted to a unified ITS control „norm“ yet.

Solution of communication in a vehicle and with a vehicle

Data currents in individual vehicle interfaces

Communication in a vehicle can be divided into inner (via busbars) and outer (radio or light waves).

Inner communication among interfaces via Ethernet type networks:

1. Vehicle state data – now usually from the CAM busbar.
2. Checking and information systems connected to an Ethernet busbar.
3. Advertisement systems represented by spots displayed on inner vehicle LCDs.
4. Public internet in vehicles – complete separation of passenger data from vehicle data has to be ensured.
5. Camera system and a possibility of on-line video transfers from a vehicle

6., 7. a 8.  – Other possible communications controlled via an on-board computer that affect the behavior of a whole vehicle.

Vehicle types from the point of view of inner communications

In the case of public transportation vehicles it is necessary to keep in mind inner data communication (not including busbars for controlling the vehicle itself, e.g. CAN) and its arrangement based on vehicle type:

• Independent vehicle – trams, trolleybus or buses that contain an on-board computer for transportation.
• Two joined vehicles equal – both trams are equipped with a „complex“ system (they are equal) and a train busbar or an Ethernet busbar is used for communication (the joint between the trams has to be modified).
• Two joined vehicles unequal – one vehicle is superordinate and has full communication equipment while the other vehicle is without an on-board computer (subordinate) and performs the checking and information function.
• Bidirectional trams – there is only one system in such a vehicle and it is equipped with cabin „A“ and cabin „B“ adapters. Two LCD terminals are connected to one system.

Data currents in outer vehicle interfaces

Radio signals are usually used for outer communication. This includes:

1. GPS (Global Position System) signal receivers – provide standard data used for position assessment according to a satellite system. Today its accuracy is a few meters (SIRF star IV and similar technologies),
2. Private radio network (PMR – private mobile radio network) – given by the type of the private network used on reserved frequencies and usually restricted to one city. Can be analogue, digital or mixed. The amount of data transferred via a radio network is usually between 10 and 32 bytes per packet in the case of an analogue network and up to a couple hundred bytes in the case of a digital network (depends on its configuration). Big packets are split into parts and transferred part by part.
3. Short independent packet of a few bytes sent to an intersection on a reserved frequency with lowered performance. Can but does not have to be confirmed.
4. Depot WIFI can work on frequencies of 2,4 GHz or 5,4 GHz. Both frequencies are usually used when the depot network is used by multiple systems (an on-boar computer system or a checking system). This network can only be used to transfer data when a vehicle is in the depot (position bound data updates). It is used for:
1. Data transfers to an on-board computer / downloading logs from an on-board computer. Hundreds of kilobytes can be transferred comprised mainly of details logged by an on-board computer.
2. Passenger counting data transfers – passenger counting data is usually downloaded once a day. This data is about 100 Kbytes.
3. Camera pictures are usually downloaded on a request – i.e. only an interval when an incident is expected to have happened. This data can even be 100 Mbytes as camera systems use hard drives with capacity in TB.
4. Tachograph records (server of the progress of a drive) – if a security camera is not included in the record its length can reach a number of Mbytes.
5. GSM technology – there has been great development thanks to utilizing the LTE communication that has significantly changed the amount of data transferred to/out of a vehicle. The APN (Access Point Name) system is usually used to increase security, i.e. inner data networks inside a GSM operator. The following systems can be connected:
1. Public internet – tens or hundreds of GB of data transferred per month
2. Advertisements and news – couple tens of Mbytes can be transferred every day
3. Advertisements on public WiFi and monitoring passengers getting on the vehicle – only information and configuration data
4. On-line passenger checking – up to 100 Kbytes a day
5. Traffic information from the transportation company or the region – up to 1 Mbyte.
6. Web service obtaining on-line traffic state information – up to 1 Mbyte.
6. Short distance communication for „waking up“ vehicles in a depot and communicating with the transportation route while on the move (FHSS). In the future, this communication will be replaced by communication based on ITS standards. At the moment, information of a couple tens of bytes is transferred.
7. Command frequencies from the vision impaired – the frequency of 86,7 MHz is reserved for this countrywide, the command itself is a mixture of bits 80 ms long.
8. Technologies for throwing of switches have a special position here – now there are three systems available in the Czech Republic, 125 kHz for induction loops, 433 MHz (simpler systems of the „garage door“ type) and 2,4 GHz.
9. Card readers (transportation and bank).

The basis of the whole system consists of a dispatching SW with a unified data and phonic interface. This SW has to be able to coordinate the above listed communications or provide transfer space with reduced band width in individual media (see below). The „CED server“ itself can consist of a number of servers – communication, application, GPS, a server for uploading data into vehicles, database, etc.. Based on the band width size these servers can be placed on one or more physical computers. Local networks with sufficient capacity are used for the purposes of running communication. Network solution and security are more of a challenge here.

A private radio network should be used for basic communication with vehicles. A combined network with data (e.g. position information every 10s) and voice transfers using one radio station is a suitable solution in this case. The advantage of this solution is that a private network is independent and therefore it can comply with safety requirements during environmental disasters. The disadvantage of this solution is its low transfer speed 1200/2400 bit/s, however, it is sufficient for position surveillance.

If data updates and checking are performed online (e.g. internet marketing, payments by bank cards in a vehicle) and if a transportation company wants to offer public internet and run WIFI for passengers GPRS/3G/UMTS networks should be used. When these technologies are utilized, they can be used to perform partial updates of vehicle informatics. This is suitable mainly for data communication with stops.

In a depot, communication with vehicles is performed with the help of a WIFI network. It is used to update data and download information about the progress of the drive (logs, tachograph, checking, etc.). Data updates require a „wide“ channel for vehicle LCD data updates (e.g. up to 500 MB). Data updates are as follows:

• Waking up at a request in the case of a parked vehicle – power supply of communicating components has to be solved
• When a vehicle is leaving/entering a depot – suitable for smaller amounts of data

Other communications include communication with switches including automatic throwing of switches, communication with intersections, electronic information panels at stops, etc.

Specific data currents in a whole transportation system

Data currents in the scope of a transportation information system have to be divided as follows

Transport control and providing transport information to passengers

A „central dispatching“ of a transportation company (hereinafter CED) is usually the center of system control. To control the system dispatchers need basic information about transportation situation – overtaking, delays, number of passengers (if possible). Based on this information they try to control transportation and ensure its regularity (we are not dealing with the reasons of these states). Dispatching now perform a new functions – they provide information to passengers using various ways to do that.

Channel for informing passengers include:

• Stop information panels or intelligent stop signs (regular departures and delays ).
• Web portals, where departures from individual stops are presented.
• Vehicle information panels and mainly solutions of continuity of individual connections.

If the system is to perform this function it is necessary to obtain vehicle position information from GPS receivers (to a limited extent also from localization loops and infrared beacons) and transfer it via either a private data (combined)  radio network of the transportation company or the GPRS/3G/LTE technology.

Preparation of data for passengers and for transportation control

Preparation of data for systems in transportation can be divided into a number of levels:

• Solution of transportation as a whole, i.e. the basic principles of functioning, whose result is creation of schedules. Efforts to reduce transportation costs result in building of junction systems that are based on continuity of individual connections which increases demands on system control.
• From this derives preparation of data for the driver and passengers, for stop panels (online and offline mode) and also for other information channels – web presentations on the internet. Each of these presentation is provided in a different form depending on the type of the information channel.
• Additional settings – transportation route control in the form of automatic throwing of switches, preference at intersections etc. In this case a connection with the schedule and route description suffices.
• Passenger checking – i.e. allocating corresponding price lists to individual vehicle drives.
• Data for advertisements or general information – i.e. their potential link to information about vehicle drives.

The way of transferring this data to vehicles is a part of this phase. These transfers usually take place in a depot where vehicles are parked. Vehicles are woken up at a set time by WIFI/FHSS and communication with the depot communication system is commenced.

Now it is possible to replace data loading in depots by gradual loading when a vehicle is on the route or in a depot using mainly the LTE technology.

Passenger checking data

Passenger checking is the third communication system that should be included in modern systems. Communication with checking systems is usually performed once a day in a depot by reading payment data. In many cases this is done by an independent WIFI channels. A newly built system that would include payments by card in vehicles should be equipped with a data channel that can be used while vehicles are on the route, it should be at least GPRS (tens of kb/s).

Additional systems for transportation

As public transportation serves a lot of people, this basic conception of on-board information systems should also include additional information and control systems. These systems have various goals and functions. They include:

• Advertisements in vehicles or aonstops (mainly passenger LCDs).
• Warning and information systems for passengers used in unexpected situations. In critical situations it is possible to use also vehicle and stop information systems.
• General news from the city, region informing about the local situation (it is necessary to solve its insertion into the system).
• Information systems for the vision impaired (now widely used).
• Internet in vehicles or at stops (vehicle WIFI).