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Technologies That Enable Congestion Pricing—A Primer

Sub-System Technologies

Photo. Traffic moving through a vehicle occupancy detection station, passing a sign reading “Speed limit 25. Do Not Stop.”

As indicated in the Functional Processes for Tolling and Congestion Charging section of this primer, the tolling process is a combination of sub-processes that require close integration. The overall effectiveness of tolling and congestion-pricing technologies will be the aggregate improvement in all steps of the process for reliability and accuracy and minimized revenue leakage and fraud. There are several related sub-systems for which a range of technology options exist, which include the following:

  • Informing and providing standard signs and lane markings to increase driver recognition and understanding of the tolling or congestion pricing across the United States.
  • Vehicle occupancy detection technologies.
  • Vehicle identification and classification systems (e.g., laser, video, digital loop, axle detection treadles, etc.).
  • Telecommunications: Roadside and centralized control equipment (e.g., in-unit, controller-based processing).
  • Automation of operations (e.g., payment and enforcement processing, account setup and management).
  • Payment systems for pre- and post-collection of tolls or congestion-charging fees.
  • Verification and secondary enforcement systems (e.g., scene image capture, mobile and portable enforcement).
  • System reliability and accuracy of DSRC systems.
  • OBU distribution facilities.
  • ITS integration.

Informing and Providing Standardized Signs and Lane Markings

As tolling systems have grown across the United States, toll facilities have been very individual and unique enterprises. With the introduction of each facility and the advent of ETC, each of these facilities has developed its own branding of its ETC package. Today, a plethora of arcane and distinct brand names for ETC exist in the United States, including E-ZPass, FasTOLL, SunPass, MnPass, and a host of other names. In an age of standardization and interoperability, these names may confuse drivers who travel across the country.

A similar situation existed in Sydney, Australia. Each toll road had its own brand name for its ETC. To solve the driver-recognition problem, a standard symbol of a green square with a yellow “E” was added to each toll lane and free-flow sign to indicate an interoperable ETC facility where any and all ETC transponders or OBUs could be read and accepted.

With the advent of potential interoperable standards such as the vehicle infrastructure integration (VII) or 5.9-GHz technologies, a similar approach should be taken to mark all interoperable facilities across the United States. This would allow each toll facility to retain its branding for local recognition, but as it adopts a national interoperable standard, a common designation is necessary, as in Australia.

Legally, each toll facility must be marked as a toll road to advise the user of the requirement for tolling. This is a common requirement across all toll facilities in the United States. Although this is a legal requirement, there are no standard road signs or lane markings for toll roads, priced lanes, or congestion-pricing areas in the Manual on Uniform Traffic Control Devices (MUTCD) to integrate the efforts and provide a common set of signs, colors, and markings as toll roads, priced lanes, and congestion pricing grow in size and numbers across the United States. In the United Kingdom, for example, the red circle with a white “C” was originally developed for the London congestion charge. It appeared on all signs and lane markings to indicate to drivers the boundary of the congestion-charging zone in London and to provide information concerning the London congestion charge.

In addition, color or road designation of these facilities—toll roads, priced lanes, and congestion-pricing areas—should be designated for ease of map making and recognition. Just as we have standardized icons, colors, and signs for Interstates and highways, we need to develop these designations for tolling and congestion pricing.

Vehicle-Occupancy Detection Technologies

A promising technological advancement that could improve congestion-pricing operations for priced-lane operations is the development of a more accurate vehicle-occupancy system. At present, some imaging software is able to read closed-captioned television (CCTV) images and discern the number of occupants. In addition, infrared sensors can detect human-heat signatures. Although more advanced algorithms and other advances in available technologies have made significant improvements in the software’s ability to identify human occupants, several inherent limitations prevent complete implementation of automated “outside the vehicle” occupancy monitoring. For example, sensors often have difficulty rendering data from all seats within a vehicle, particularly in the dark or when one of the passengers is a small child. Further complications arise in non-barrier-separated roads where movement between lanes has minimal physical restrictions. For automated enforcement to be implemented, sensors must achieve near perfect accuracy, which thus far has not been possible to attain.

One potential solution is to instead focus on occupancy monitoring from inside the vehicle. Seatbelt and air-bag sensors are already standard equipment on today’s vehicles, monitoring front-seat occupancy via mechanical seatbelt closure sensors and weight/pressure sensors installed within seats. In the future, additional sensors could be installed in the rear seat, allowing the vehicle to have a complete analysis of the number of occupants in the vehicle. Additional advanced sensors, including light-emitting diode (LED) and infrared imaging, could be added to ensure a more accurate measurement. The in-vehicle system could communicate occupancy information with sensors imbedded in the infrastructure via a radio transponder/receiver system, GPS, or cellular signal to allow single-occupancy and high-occupancy vehicles using HOT lanes to be assessed the appropriate charges.

Vehicle-Identification and Classification Systems

The task of vehicle classification for congestion pricing varies with the type of scheme and primary technology used. For manual or semi-automated toll lanes, in which vehicles are confined to a single lane at reduced speed, classification can be measured by size, weight, or number of axles. In these situations, devices such as weigh-in-motion (WIM) detectors, treadles, or lasers can be used with relative accuracy.

Once a free-flow environment is introduced and vehicles are required to be classified at full speed and in a multi-lane environment, the ability to classify with the use of technology is reduced, along with the range of technologies available. Current axle treadles and WIM technology do not provide sufficient accuracy to classify vehicles in this type of environment, and a size-based classification system is therefore required.

There are currently two sufficiently reliable methods available to classify vehicles by size in a multi-lane free-flow environment: scanning-laser technology and stereoscopic-video technology. Digital loops also provide an option but are affected by lane-change movements and do not provide the range of classification available with laser and video systems.

The technologies for classification are another area in which standardization is needed across all toll facilities in the United States. A common reference system would assist drivers in knowing the charges they will incur. Current classification systems and their application create confusion and uncertainty in the minds of drivers. Only from a national perspective can this effort be directed and then implemented by states and toll agencies.

Telecommunications: Roadside and Centralized Control Equipment

Photo. Interior of an office showing an example of where roadside processing equipment is kept.

Roadside processing equipment.

Photo. Close up view of centralized processing equipment showing multicolored cables and wires, and various machines.

Centralized processing equipment.

Photo. People wearing headsets while at work on computers as part of back-office operations at a monitoring station.

Centralized processing equipment.

All congestion-pricing systems require the continuous processing of large volumes of transactions. Depending on the charging scheme and primary charging technology used, the complexities and volumes of these transactions can be managed in different ways to achieve a suitable balance between system reliability and operational cost.

One major area of consideration is the balance between roadside and centralized processing and the communications architecture developed to support these processes. Decisions should be based on several factors:

  • The volumes of data that need to be moved around the system.
  • The availability, reliability, and cost of communications.
  • The number, security, and accessibility of roadside installations.

Congestion charging schemes rely on large volumes of transaction data passing between a network of roadside facilities and the back-office systems. Depending on the type and structure of the system, this data may be relatively low-volume, character-based files, or much larger (for ALPR) digital-image files. These system requirements will have a significant influence on the architecture of the system and, in particular, the communications networks. For example, conducting ALPR processing at the roadside may significantly reduce communications and storage costs if the system provides for this type of operation; however, this requires a greater level of functionality within roadside equipment that may prove too costly to provide at a large number of locations.

These decisions and the resulting system architecture can have a major influence on the cost effectiveness of the entire system. For example, the London congestion charge is based on a high level of centralized processing with large volumes of data being transferred daily from many roadside facilities. This leads to higher costs, with recent technology reviews and trials highlighting the potential savings that could be made through a more efficient architecture. ALPR-based systems have the most to gain from improved architecture design, having the highest potential data requirements. DSRC systems that use an ALPR enforcement component would be the next highest user, with VPS and cell systems most likely to have the lowest demand.

Recent trends in the development of the primary DSRC and ALPR equipment have led to the consolidation of some processing within these units, thus reducing the functions of roadside control units and further improving cost efficiency.

Automation of Operations

The major operational costs of congestion-pricing systems result from the continuous processing of large volumes of transactions. Depending on the charging scheme and primary charging technology used, these transactions and processes can be automated to reduce cost and improve the overall efficiency of the system. A key objective is to minimize manual processing, particularly where there is no direct customer contact.

The use of OBUs is a major contributor to reducing operational cost across most free-flow facilities. As the most reliable means of automating vehicle (or account holder) identification, this technology reduces the level of manual processing required and thus minimizes cost.

Other areas of automation include account setup and management processes through interactive voice response (IVR) and the Internet, ordering of statements, and account top-up facilities.

The selection of appropriate systems to automate back-office functions is critical to developing a cost-effective road-charging system. Congestion pricing is based on high-transaction volumes and relatively low-transaction values that lead to a focus on small costs to ensure a cost-efficient system.

Payment Systems for Pre- and Post-Payment of Tolls and Charges

There is a wide range of payment options available, and the selection of an appropriate package of options needs to address the specific needs of each scheme. A key issue is the balance between providing security of payments at a reasonable cost and providing user convenience.

Where manual or machine-based payment options are available, the use of cash and standard card-payment options is feasible, and although the management of cash payments involves some cost to the operator, the convenience and anonymity of cash addresses a key concern of some users.

For most electronic tolling and congestion-pricing systems, the primary and preferred payment mechanism is through customer accounts. These provide greater security of payment for the operator (as users are generally required to prepay and provide bank account or credit card details) and reduce the cost of operation. Accounts are also more convenient for most users, because they are not required to make individual payments for each transaction. Account-based payments can be used with any OBU or ALPR-based system and are the most common form of payment for free-flow toll facilities.

A further option is the use of smartcards, as used in the Singapore ERP system. These cards are used with the vehicle’s OBU, and payment is debited from the card balance. This provides a further level of convenience that is preferred by some customers, and as the balance on the card is prepaid, there is a degree of security for the operator. The main disadvantages are the increased complexity and cost of the OBU and the need to provide real-time roadside processing of payments.

One advanced electronic-payment technology with potential application in congestion-pricing programs involves the use of contactless bank cards. Contactless smart bank cards, such as the Visa Wave or the MasterCard PayPass, are being distributed by several U.S. banks already, and more plan to follow. These cards allow payment by radio frequency identification (RFID) transaction—just tapping the card on the reader—instead of requiring the magnetic stripe of the card to be run trough the reader (a slow and fraud-prone process). EMV is a protocol, developed by Europay, MasterCard, and Visa (EMV), for authenticating credit and debit card payments at point-of-service (POS) terminals and automated teller machines (ATMs) through the use of interoperable chips.

Although it has failed to gain traction in the United States, this standard is used throughout most of the world, including Europe and Asia. The version of EMV used on the contactless bank cards, called contactless EMV, uses an encryption algorithm that makes them essentially fraud proof. In congestion-pricing programs, the contactless EMV cards could be used in OBUs that act as the toll-tag transponder. OBUs with contact smartcard card readers are in use in Singapore, and the Norwegian company Q-Free built OBUs with contactless card readers that were used at the 2006 Winter Olympics in Turin, Italy. By using such transponders and cards, congestion-pricing programs could avoid having individual user accounts to administer—users would pay directly by bank card.

Secondary Enforcement

Photo. View of four cars on a road, taken by an ALPR enforcement camera.

ALPR enforcement.

ALPR is effectively the foundation of all electronic free-flow charging, because it is the only common point of reference for all vehicles passing through a toll checkpoint or zone boundary.

In most free-flow tolling applications, ALPR is used only as an enforcement tool, with the majority of users charged and verified through an OBU. Even in this situation, secondary enforcement systems, such as color-scene images, are recorded for evidence and to back up the basic ALPR records.

However, in situations in which either ALPR is the primary technology or there is a need for further enforcement backup, other backup systems and technologies can be used, such as front and rear ALPR systems or digital video recording of traffic that can be accessed later to assist in identifying offending vehicles. These systems can provide an alternative view of traffic from the primary ALPR systems and can overcome adverse environmental conditions such as sunlight or shadow effects.

System Reliability and Accuracy of DSRC Systems

Pricing systems using vehicle-based OBUs are used widely across the world for a range of tolling and road-charging applications. These systems generally use a microwave signal at or around 5.8 GHz to provide the critical vehicle-to-roadside communication function. The most widely used standard for this frequency range is the European CEN-278 standard.

As the planned role for vehicle-to-roadside and vehicle-to-vehicle communications becomes more widespread (i.e., moving into dedicated safety systems, traveler information, and other ITS applications), the 5.8-GHz standard is being superseded by a standard in the range of 5.850–5.925 GHz. This developing standard, known as WAVE, has greater range and greater multi-channel capability. Although there are no current road-charging applications in operation, it is likely that this standard will replace and enhance current systems over the next 10 years or so.

In the United States, the implementation of DSRC-enabled devices serves as part of the VII initiative, which brings together vehicle manufacturers, government agencies, and professional organizations in the design of architecture, standards, policies, and potential business models of a system that will enable vehicles to communicate with each other and roadside equipment. It is envisioned that VII transponders will be installed soon in all vehicles and that roadside equipment will be deployed at major intersections and along roadways throughout the nation to form a nationwide network. Applications for VII include public safety, traveler information, and demand management. The vision for VII is to deploy roadside units throughout the country, thus creating a uniform, nationwide data network. Combined with GPS, all connected vehicles will know their location and have the ability to communicate location, traffic conditions, and other information to the system. The ability to exchange such information could be useful in congestion pricing.

OBU Distribution Facilities

The distribution and management of OBUs for DSRC and VPS-based systems incorporate a range of technologies and systems designed to address the specific requirements of particular schemes. The majority of OBUs would be distributed from a central facility by mail, by customer collection, or through agent networks. However, the use of vending machines has helped improve distribution and availability, as is the case with the Austrian Motorway toll system.

Banks and financial institutions also distribute tags, OBUs, and transponders. For example, in Spain and southern France, the VIA-T project proved that drivers could sign up for toll accounts through banks and financial institutions. These institutions provide the OBUs and the account mechanism for drivers by linking payments to (a) the bank-issued credit card, (b) a person’s checking account (direct payment), or (c) a savings account/debit account. Just like the issuance of a credit card, the OBU was dispatched from a central depository to the individual by express and registered mail.

As toll roads, priced lanes, and congestion pricing become more common, the business model for standardized OBUs should change, as well as the business model that people use to secure them.

ITS Integration

The level and type of ITS integration will depend on the type of pricing system adopted and the payment structures and technologies used, but opportunities exist to integrate at many levels. Another major area of ITS integration is the use of pricing-system data to provide travel time and congestion information. One of the best-developed systems is the Italian TELEPASS system that has been in operation on the motorway network for many years. The large numbers of OBUs continually moving across the motorway network are tracked by purpose-designed stations to provide real-time travel-time information, linked into traveler information systems.

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