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This appendix discusses the background information for the system choice for the traffic data components. First the properties of the traffic data itself are analyzed. The second section discusses the collection methods and the third section discusses the communication types with the corresponding data receivers.

A.1 Traffic Data

Traffic conditions can be described in many different ways. The final method should match the user needs. Because these needs are not assessed yet an overview is given of the most likely used data content. In order to use traffic data for improved route choice the data must have some qualities:

 Reliable secondary and urban roads. The ways the data is collected will also depend on the wishes for the spatial resolution

 Definitions of traffic condition types – this is used to make a choice on how the traffic conditions are defined. There are several possibilities for example in terms of delay, traffic speed, relative traffic speed to the maximum speed or I/C-relation. A choice on this attribute will also affect the data collection method.

 Refresh rate – the third important property is the refresh rate. It tells how often the information is renewed and thus how up-to-date the data is. A higher refresh rate will give better information but more information must be sent to the navigation system. The refresh rate is also limited by the collection method.

All three properties are important for the quality of the data. Combined with the properties some criteria are available to choose for the type of data and the way this traffic data is collected.

A.2 Traffic Data Collection

Collection of traffic data can be done in many different ways. There are three types for data collection, namely infrastructure based, vehicle based and driver based. Infrastructure based data collection can be done using induction loops or video detection systems. Infrastructure based data is mostly collected and processed by the road operator. An advantage of this method is that the data is often of high quality and relatively fast available. A disadvantage is the amount of data is huge and thus the processing effort what is needed is high. Another disadvantage is that most of the time only highways are equipped with sensors while secondary (regional) roads are not. This way the spatial resolution is not high and the possibilities for good route choice are limited. Another option is the use of vehicle based sensors. Examples of this type of data collection are probe cars (for example already used on cabs in some cities) or using the navigation systems as sensors. Both options need communication from the vehicles to a central server which can be a disadvantage. An advantage is that there is no dependence on road operators as a source for the data and with enough sensors (probe cars or navigation systems which can give feedback on their location and speed) also the

BIJLAGEN Intelligent Transport Systems 2, University of Twente | Group 4 – K. Kant & S. Beumer 37 secondary roads can be used. This is also a disadvantage, because enough cars need to be equipped

to get reliable data.

The third option is the ‘driver’ based sensors. This is not, as one would expect, that the driver tells its location and speed, but something which is largely used by the drivers, the cell phone. Mobile phones can be used for acquiring traffic data. For this method the fact that all cell phone (that are switched on) are connected to the closest antenna is used. Because cell phones are in movement, it is necessary for the service provider to be able to track these in order to find the antenna to which the phone will connect. This way the cell phone user has always the best possible signal and at the lowest signalling costs possible. This tracking of the cell phones can also be used for another purpose as drivers in cars often have their cell phone switched on. Combining the data from several users and filtering the data for cell phones that are expected to be in a car, an estimation can be made on traffic conditions. Especially mean speeds (and thus grades of congestion) can be acquired using this method. Many researches has been published relating to this matter. Especially about the filtering of the data to take only those cell phones in consideration which are in a car and the reliability of the data. He resolution of the data depends on the area one antenna operates. In urban areas a radius of 200m can be achieved up to a 5 – 20km cell radius in rural areas (Caceres, 2007).

One advantage of this method is that minimal additional components are needed for the individual drivers. A central server must get access to all GSM-connection data and must process this to estimate traffic data like mean speed at all roads. The spatial resolution is likely to be high because a mobile phone is on board of the most vehicles and most heavy traffic is expected in urban areas with small antenna areas (thus high resolution). Different types of traffic conditions can be defined using the speeds of the cell-phones in relation to the speed limits. This way an estimation can be made on traffic conditions in a number of degrees (e.g. light, medium and heavy traffic). A disadvantage is that the methods to retrieve traffic conditions from this data are not always as reliable as one would want to, but the method can give usable results for highways and most regional and main urban roads.

Table A1 gives a summary of the advantages and disadvantages of the possible methods for traffic data collection. Driver based – cell phone tracking  High resolutions possible

 No dependence on road Table A1 – Summary of types of traffic data collection

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A.3 Traffic data communication & receiver

For this function a communication channel and a corresponding receiver are needed. There are several combinations that can be used. Possible solutions for the communication channel are RDS-TMC, TPEG and VICS. Pre-trip updates, radio broadcast, infrastructural based communication and mobile phone systems are possible for the communication devices.

RDS-TMC is a channel which can broadcast TTI as data on FM transmissions using a Radio Data System (RDS). It has a limited data transmission capacity. This limits the implementation of this channel when a lot of (multi modal) TTI has to be transmitted. RDS-TMC uses a radio as a receiver. If this radio has multiple frequencies, this improves the capabilities of the communication channel.

TPEG is a channel which provides more data transmission capacity. It uses all advantages of RDS-TMC and improved on the aspects that were considered disadvantages. It is more aimed at the multimedia broadcasting environment. TPEG can use different delivery technologies such as digital audio broadcasting (DAB), or internet. The receiver for TPEG can be implemented in the navigation system. VICS is the Japanese communication channel which has multiple methods for the distribution of information. The problem is that it is proprietary. It is only known that it uses an FM channel and radio and infrared beacons for the broadcasting of travel time information.

Type Advantages Disadvantages

RDS-TMC  Infrastructure is already available

 Cheap Table A2 – Summary of types of traffic data communication

For the data communication devices also a choice has to be made. The first possibility is to update the navigation at home with an internet connection. This of course has as big disadvantage that no update is possible during the trip, resulting in bad information. Another option is to use radio broadcast. This is an easy to use communication possibility at the moment used for TMC broadcast. A disadvantage is that is not possible to personalize and the bandwidth is limited. To address to this problem the communication devices can be more location orientated using infrastructure based communication devices like infrared or short radio transmission. This is costly to implement because it must ne build up from scratch. Therefore it is not a realistic option.The UMTS (Universal Mobile Telecommunications System) method uses mobile phones and their connection through UMTS beacons to transmit data. It requires that all equipment is modified for UMTS operation and services.

The best communication device is the use of the mobile phone standards like GSM, GPRS or UMTS.

The information can be personalized and no large investments are needed in the systems infrastructure as the mobile phone network is already available in most countries. The disadvantage that there is a dependence on the mobile phone company is expected to be minor, because cooperation is already needed for the traffic data collection.

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Type Advantages Disadvantages

Pre-trip update (internet)  No additional communication channels needed

 Not available during the trip

 Not up to date with longer trips

Radio broadcast  Infrastructure already exist

 Large communication area

 Difficult to personalize information

 Available for everyone (no possibilities to limit access) Infrastructure based

communication (infrared, short radio transmission)

 Location based information possible

 Costly to make new infrastructure

 Difficult to implement nationally

Mobile phone (GSM, GPRS, UMTS)  Individual information possible

 Possibilities to charge users

 Universal system, can be used in every country

 Infrastructure already available

 Costs for every data transmission

 Dependence on mobile phone company Table A3 – Summary of types of communication devices

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