Radio-wave-based vehicle identification with radio frequency identification (RFID)

RFID technology has been used widely in industry and logistics for many years. This technology also offers innovative approaches when it comes to the electronic recording of vehicles on the road. That is why authorities across the globe are looking into the possibilities provided by RFID-based, electronic vehicle identification. Radio-wave-based vehicle identification primarily serves to support camera-based systems with the aim of maximising the success rate for the number of vehicles recorded.

The classic camera-based vehicle identification systems have, however, also been significantly improved upon: improved recording techniques, high-resolution images and advancements in terms of digitalisation have all contributed to the increase in performance of this technology.      

There are various different motives behind the desire to achieve a comprehensive and clear identification of vehicles in moving traffic: for some countries it is about recording traffic flows and using this information to introduce use-related toll charges, or to detect and punish traffic infringements. Other countries, by way of contrast, want to take action against the misuse of vehicles for criminal or even terrorist activities.  

There are currently three RFID systems available to achieve these objectives (for use in moving traffic and thus with a reading range of at least ten metres):

Passive RFID systems

These include systems fitted with a transponder but without their own power source, such as a battery. If these transponders are located within the reading range of a reader, they absorb part of the energy emitted to supply their own chip. The rest of this field energy is used for a reply. 

Semi-passive systems

In this case the transponder has its own power source to supply the computer unit with electricity. Despite this, communication is also passive with these systems: the transponder only emits information via a signal when it is requested to do so from the other device (a so-called “reader”).

Active systems

The transponder also has its own power source in this case. Unlike semi-passive systems, this transponder actively emits a regular signal. If it is within range of a reader, this signal is recorded and processed.

The demands of the user determine the best system to use.

Which of these three systems is best for RFID-based vehicle identification? At present there is no one-fits-all solution. Instead, each system has its own advantages and disadvantages.

Passive RFID systems have the benefit of low-cost transponder units, with each unit costs starting from less than 1 euro. This benefit is, however, countered by the high investment cost of the reader infrastructure required.

In addition, passive systems are very sensitive to metallic environments (reflect radio waves) and moisture (absorb radio waves). This can lead to a noticeable loss in range and thus to non-detection in real traffic situations. The only devices to provide a buffer against this are special, high-performance transponders with specified ranges of 13 metres and above.

As a result, toll systems within the European Union only use semi-passive systems. These systems have established themselves as the tried and tested option in various member states due to their reliability and high detection rate, even under diverse framework conditions.

Within the European Union, considerations go far beyond the borders of individual countries: the EU has the long-term aim of achieving the cross-border calculation of toll charges based on standardised, semi-passive technology for transit traffic.

The EU directive concerning the “interoperability of electronic road toll systems within the Community” from 29th April 2004 specifies the binding parameters for this: satellite tracking, mobile communications in line with the GSM/GPRS standard and microwave technology (5.8 GHz). The objective is to achieve a coverage rate of 100% in order to guarantee a fair distribution of the charges across all road users who are liable to pay. 

Choosing the correct system and making the necessary investment is, however, not all that is required to establish an RFID infrastructure: what about foreign vehicles without transponders? Or what about vehicles whose transponders don’t work, for whatever reason?

In order to be able to reliably identify these road users too, there needs to be an equally dense network of cameras in addition to the RFID infrastructure to help capture and identify license plates.  

An overview of the features (for and against)

Is camera-based vehicle identification not sufficient?

In theory, vehicles can be identified solely through the use of cameras. In some large cities in Sweden, for example, the country has switched off the radio-based system and only uses camera systems. These camera systems have been consistently improved in recent years and now offer a very high coverage rate.

The problem: a pure camera-based system captures the vehicle and the driver, and identifies the vehicle based on the alpha-numeric code on the license plate. At the moment of recording, it cannot be ensured that the license plate identified actually belongs to the vehicle in question. Fake license plates or license plates taken from other vehicles cannot be directly exposed in this way. Thus, when a pure camera-based system was introduced for the congestion charge in London between 2008 and 2009, the number of fake license plates increased by around 60 percent – thus the system can thus be easily tricked in this way.

On the other hand, an additional electronic capturing of the data using RFID makes it considerably harder to succeed with this kind of deception. Last but not least, the location of the transponder is also decisive for the benefits of the system in question.

Where should the RFID transponder be placed on the vehicle?

In the case of semi-passive and active RFID systems, the answer is simple: the transponder modules, or so-called OBUs (on-board units), required are installed into the inside of the vehicle or fitted retrospectively.

When it comes to passive RFID systems, however, there are various different approaches. License plates are available with integrated transponders; alternatively, “electronic vignettes” can be attached to the inside of the windscreen. Once again, the best solution depends on the needs of the user.

If the only requirement is to match the product lifecycle of the license plate, the best option is an RFID transponder on the license plate, as it represents a fixed single unit. The journey that the license plate makes from the day it is registered to the day it is taken off the road can be fully tracked using the data transmitted by the transponder.

Despite this, this solution is not able to identify the vehicle with total reliability, as the London example shows. Despite the transponder, it is relatively easy to conceal the true identity of the vehicle by simply changing the license plate. Alternatively, foreign license plates without transponders can be used. Thus it is easy for criminals and terrorists to slip through the system unnoticed.

An RFID vignette can close the loopholes in the system.

An “electronic” RFID vignette on the inside of the chassis makes it possible to identify the body of the car and, in contrast to an external license plate, the RFID vignette is also less accessible and therefore not so easy to swap. In regards to this solution, the focus has to be on both the range and the security features. Vignettes cannot be transferred from one vehicle to another without damage and should be fitted with suitable features to prevent counterfeiting. 

In addition, the RFID vignette can be printed with data relating to the vehicle in question, for example the alpha-numeric code on the license plate. In this instance, a simple visual inspection (by the police during a vehicle spot check, for example) is all it takes to recognise a fake license plate.

In order to close potential security loopholes posed by foreign vehicles, it is also possible to affix an RFID vignette to the vehicle as it crosses the border to make it visible and identifiable within the system in use. At the same time, this makes it easier to record and collect toll charges, including those accrued by foreign road users. 

But the true value of an RFID vignette is shown when it is used in conjunction with a combined reader/camera system. This configuration makes it possible to identify a vehicle using RFID in moving traffic, whilst also using a database search to find out whether the license plate recorded by the camera actually belongs to the vehicle in question. This level of configuration currently offers the best solution for electronic vehicle identification, albeit at the greatest cost.  

An overview of the features (for and against)