Correct assignment of road user charges in line with true road usage and cost of road operations is a priority across Europe, reflected also in numerous working groups and a specific European Directive solely targeted at interoperability. European countries faces the requirement of rapid road development which needs stable funding and proven technology. The satellite based charging technology could be one option to generate maximum funds in short time.

Satellite based tolling allows implementation of several business models. The choice depends on the legislation on one hand, and on the maximization of revenue on the other hand. The typical models that are described below may, in addition, be varied with charges by time and place, contributing to management of traffic flows. In all cases, an OBU (OBU = On-Board Unit) is installed in the vehicle to determine the position, communicate with the back office and to enable enforcement of payments.

The "Virtual Toll Plaza"
A "real" toll plaza is a major building with manual or mixed electronic - manual tolling, or may also consist of a portal (gantry) across the road which offers electronic tolling in free flow. The "virtual" toll plaza is not based on any physical infrastructure but is just stored in the memory of the electronic toll OBU. Every time the vehicle passes a virtual toll plaza, the particular road section is charged. The advantage is that there is an "official length" defined with each plaza, so no differences are there in the measurement as they may occur from vehicle odometers. The disadvantage lies in incomplete charging in case of a very distributed network. For example, in a city with many side roads, other business models become more suitable. (Of course it is still much cheaper than building real toll plazas or portals in that density!).

The "Zone based" model
On passing a certain zone border, the charge is levied for entering the zone. This may be an interesting model for city tolling, or even for an entire country where the country is divided into zones or quadrants. In any case, zone based mechanisms must be implemented at borders between countries or between different charging models. The property of the zone is set such that no overcharging takes place, e.g. a few meters of grace distance at the border of the zone.

The "Kilometer price" model
The kilometer price model allows charging by the exact distance driven. The position of the vehicle is determined every few seconds and the difference calculated. This method allows the highest theoretical revenue, as the entire road network can be charged and bypasses are not possible. At the same time, also precision is the highest achievable in tolling because it is not necessary to simplify the network.

"Thin Client" vs. "Smart Client" architectures
The tolling industry is currently having a lively debate whether the OBU should just send position recordings to the central system ("thin" OBU) or whether the OBU should run  all calculations and only transmit the result ("smart" OBU). Both versions have strong points, e.g. "thin" OBUs do not contain algorithms and all charging software is in the back office. Any change to the road network only takes place in one central system as opposed to hundreds of thousands smart OBUs. On the other hand, smart OBUs are lower on communication cost and are typically better accepted for fear of too many data being present in the central system. Due to technical advances in the last years, there is typically no cost difference between the two versions.

Extendability of the network
In most architectures, it is easy to update the memory of the OBU, and any extension or changes of the tolled network can be implemented in the toll system without need for construction or rollout of a different system. Even the business model can be changed easily since the software update of the OBU is also possible at any point in time.

Interoperability and European regulation
The European Directive 2004/52/EC incentivises the use of satellite ("GNSS") technology, but also permits the continuation of DSRC systems due to the fact of the widespread use of DSRC in toll plaza environments e.g. France, Spain and Italy. "But Pan-European interoperability can only be provided by satellite based units. All satellite based units deployed are also equipped with DSRC interfaces which may work in other systems, provided operators agree to accept the various devices", says Max Staudinger of EFKON.

Reaching Maturity in Truck Tolling
Currently, the satellite based free flow system with the highest revenue is the German truck tolling system. The revenue of more than 4,400 million Euros per year is almost double the revenue of all other European free flow truck tolling systems combined (Austria, Switzerland, Czech Republic, Slovakia). With these numbers, satellite toll systems collect more than 83% of Europe's free flow truck tolls since more than 5 years. (Switzerland utilizes satellites to back up odometer reading). The system in Germany was developed from scratch and has functioned (though with a delay) at high performance since the very first day. Satellite based OBUs have come down in price by more than 50% since the start-up of the German system (13% per year). The same holds true for DSRC, but the impact is higher for satellite systems as more intelligent devices need to be in the vehicles.

Satellite based systems compare to any other system in a way that they can be used in any place, can be set up in very short time for complex business rules and do not require local permits to build or personnel to maintain. The intelligence is shifted from the roadside to the vehicle and allows rapid generation of funds for further improvement of the road network.

Written by Max Staudinger and Hannes Stratil