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|Rui Barradas Pereira, GMV
|Year of Publication
It is foreseen that traditional ways of road tolling will be substituted by solutions based on positioning by means of GNSS. The use of GNSS for Electronic Tolling Collection (ETC) has many advantages with respect to other technologies as it allows for a flexible and scalable system with minimum specific roadside infrastructure. This translates directly into a simple and cost efficient system. In fact, the interoperability directive 2004/52/EC adopted by EU in 2004 prescribed the development and deployment of a European Electronic Tolling Service (EETS), recommending the GNSS technology as the one to be adopted.
Road and urban tolling based on GNSS implies that the position and trajectory of a vehicle is determined using GNSS in order to decide if the vehicle must be charged or not and to compute the charging value. This must be done along with the determination of an integrity level and the acquisition/generation of evidences that can be used to prove that the charged amount is correct.
ETC applications are implemented using On Board Units (OBUs) developed for that specific purpose that use GNSS data to compute the charging values. Some OBUs also integrate information from additional sensors - such as gyroscopes, accelerometers or OBD (On-Board Diagnostics) input data - in order to increase accuracy and minimize incorrect charges. In particular, to prevent the charging of vehicles that are not using the road or urban area subject to toll.
The data collected by the OBUs is usually sent to a central server that consolidates the payment information for the users of the system. These systems require a communication channel between the OBU and the central equipment. Cellular network is generally used but other means of communication can also be used such as Wi-Fi, Bluetooth, DSRC. Cellular network communication relies on existing public networks while the other communication methods might require specific road side infrastructures.
These OBUs can rely on Satellite Based Augmentation Systems (SBAS) like EGNOS or WAAS to achieve better accuracy and to make decisions based on the integrity and availability provided by those systems. There are also devices equipped with built-in autonomous algorithms that handle and decrease the effects of local errors, such as non-line-of-sight multipath. These kinds of mechanisms may guarantee an acceptable protection level (PL) for a ETC system, dismissing the use of additional sensors that would add complexity and cost to the systems.
In terms of hardware requirements the devices used for tolling are very similar to vehicle trackers. To support tolling, a device should have GNSS support and have wireless communication abilities either through WANs (e.g. cellular network) or LANs (e.g. Wi-Fi, Bluetooth, DSRC). Some systems can have user interface, although this is not mandatory for tolling applications. The only specific requirement - that might not be present in vehicle trackers - is integrity support, since tolling is a liability critical application. Depending on the architecture and on the pricing complexity, the OBU might have different requirements in terms of processing and storage capabilities.
The electronic fee collection (EFC) process implemented by this application can be divided in the following steps:
- Position Determination - Determination of the PVT (Position, Velocity and Time) using the GNSS data available that might be combined with other sensor data such as gyroscopes, accelerometers or OBD.
- Road Usage - Determination of the roads features used by the vehicle being tolled. This information includes the time at which the vehicle used those road features.
- Charge Calculation - Determination of the price to be charged to the owner or user of the vehicle.
- Payment - Payment of the charge
Although the main steps described previously are common to all EFC applications, the architecture of these systems can differ depending on which part of the system they are run: in the OBU or in the central system. Some possible approaches are.
- Fully Centralized: In this architecture the OBU is a very light footprint and cost-effective device, with a reduced processing power. Its only task is Position Determination, i.e. to calculate the PVT (Position, Velocity and Time), to combine it with the identification of the vehicle and to transmit the data to the central server. The central server receives the PVT data and is responsible for the remainder of the EFC process (road usage calculation and charge calculation).
- Partially Centralized: The OBU uses the PVT to calculate Road Usage and sends this information to the central server.
- Fully Decentralised: The OBU makes the Charge Calculation step calculating the charge. This architecture might even include the payment in the OBU using electronic purse cards.
The choice of the adequate architecture is a trade-off between the cost of OBU and the operation cost. Centralized architectures can use cheaper OBUs with less memory while decentralised architectures will require more processing power to calculate road usage and the charges, as well as more memory to store context data such as maps and tariff information. Centralized architectures require more upload bandwidth to send road usage information to the central server, whereas decentralized architectures require more download bandwidth to update context data. Other relevant factors in the choice of architecture will be privacy and enforcement. These are usually conflicting factors since centralized architectures might raise privacy concerns since they are more easily monitored for fraud. Conversely, decentralized architectures are more protective of the user privacy, hence more difficult to monitor for fraud.
These applications are considered liability-critical applications.
The goal of this kind of application is to have an “error-free” charging computation with high utility value, making it acceptable for institutions and users. Providing integrity of the computed position allows ensuring that vehicles are not charged incorrectly. This is done by establishing a threshold value for the position protection level, i.e. if a given computed position exceeds a computed threshold, then that position will not be used to compute charging values.
From the user point of view, tolling applications work in a transparent way, since the user doesn’t have to operate the OBU installed on its vehicle. Eventually the user receives a monthly detailed report justifying the charged amount.
GNSS-based tolling relies on the detection of road features that will determine the amount to be charged, as a combination of the road usage and related information.
The road features that are normally used for charging purposes are
- Zone - The car is charged when inside (or outside) a geographical zone.
- Corridor - The car is charged when it goes through a geographical corridor or a sequence of corridors. A corridor normally corresponds to a road (although it can correspond to a set of parallel roads). A corridor is usually a rectangle that is crossed by the vehicle longitudinally. Direction might be relevant depending on the charging policy.
- Virtual Gantry - The car is charged when crossing a virtual perpendicular line on the road, in the same way as in going through a toll booth. A virtual gantry consists of two quadrilaterals joined by one side. The common side defines the line that when crossed triggers the charge. One of the quadrilaterals signals that the vehicle is entering the gantry and the other its exit. The vehicle needs to cross the entry quadrilateral, the virtual line and the exit quadrilateral in sequence in order to be changed.
Several road features can be combined to make more complex road features.
Road's features are then combined with other information to determine a charge value. Some of this information can be:
- Vehicle Characteristics
- Time and Date
- Actual distance run - Determined by the GNSS information.
- Theoretical distance run - Determined from maps based on the features crossed.
The concept of road tolling can be used for other similar applications such as CO2 charging and pay what you drive insurance schemes.
The main tolling applications providers are
- Intelligent Mechatronic Systems: Has developed the DriveSync® product which is a modular vehicle telematics system that uses Global Positioning System (GPS) and cellular technologies to track vehicles.
- GMV: Developed the allroadTM product which is a standalone OBU which guarantees a 99,99% of reliability bellow the established protection level (22 m in open sky environment and 75 m in urban environment).
- Satellic: Developed a platform that implements flexible road tolling solutions based on free-flow-systems.
- Skymeter: Has developed an OBU that is installed along with an LCD display to show the charged tolling and some other informations.
- Toll Collect: Has developed and is running the toll billing system for trucks (LKW-MAUT) on German motorways.
- Kapsch TrafficCom: provides on-board units that are read/write devices designed to ensure high data security and integrity with high speed internal processing.
- EFKON: The OBU autonomously determines the position of the vehicle, identifies road sections subject to tolling according to predefined rules, calculates the charge value (if any) inside the OBU, and transmits the result to the toll center.
- Siemens VDO: A hybrid OBU (on-board unit) in the vehicle manages both microwave and satellite-based toll systems.
- ^ Simulation tools for the assessment of GNSS based Road Tolling Systems, J Simón, J. Caro, J. Cosmen, GMV
- ^ Directive 2004/52/EC of Parliament and of the Council of 29 April 2004 on the interoperability of electronic road toll systems in the Community
- ^ Architecture Discussion for GNSS-based Electronic Fee Collection Systems: Fat vs. Thin OBU?, P. Gomes - GMV, R. B. Pereira - GMV, H. Appelbe - Mapflow, A. Mozes - Logica, ITS Europe 2007
- ^ ISO/TS 17575:2010 Electronic fee collection -- Application interface definition for autonomous systems
- ^ GNSS Road Pricing on Wikipedia