Author: Francisco Medina Abellán
The highest aspiration of any toll system is to ensure the detection (and associated payment recovery) of any vehicle moving under its sphere of influence. If, in addition to that, the system reliability and availability achieved is 100%, welcome to the perfect system!
When the goal is to guarantee 100% up-time (availability), it should be approached via the use of stable and well performing software, high-level hardware and whats known as a fully redundant solution.
Multi-lane free-flow (MLFF) tolling is popular because it eliminates the need for toll booths and keeps traffic flowing well, as users do not have to slow down to go through any charging points (CPs). But on the other hand, MLFF has a major disadvantage in the possible reduction of income if the system being deployed is not 100% reliable. In free-flowing traffic, there are no second chances to identify a vehicle.
In a fully redundant solution, every subsystem (detection and classification, OBU reading, video enforcement and system management) is designed to be 100% reliable, via the construction of new algorithms, software architectures and hardware developments.
In its standard configuration, an MLFF system already has sensible redundant aspects within the most critical elements used for recovering information. Why not apply this concept to all components then? Why not consider that a small investment in terms of technology and equipment may be recovered in just a few days of operation?
For a well-known tolling expert, Tecsidel, its modular architecture concept for standard MLFF helped it to find the best technological solution to create a fully redundant MLFF system.
It was obvious to Tecsidel that fully interchangeable equipment at all CPs within a tolling system was critical to achieving reliability.
The companys main objective is to support the maximum feasible degree of system degradation. It does this in a variety of ways across numerous key parts of an overall system.
How to build in redundancy
Tecsidel has re-designed its electrical rack to power-isolate equipment during any potential power supply disruption or electrical surges.
The company has also built in fault-tolerant network connectivity using an automatically managed dual-balance connection point on every server.
Dual communication (wire as main, wireless as backup) channels between different levels from lanes to the back office is also a key part of Tecsidels system.
It is also important to ensure that vehicle detection and classification can still be done even if some detectors fail. Every vehicle not detected equals a loss of revenue. Likewise, for MLFF systems that rely on reading toll tags in vehicles, Tecsidel ensures that all of its OBU-reading technology is dual-concept.
To prevent the loss of images when a video processor fails, all cameras related to one direction of travel are connected to one image acquisition processing (IAP) unit, and additional units are introduced as hot back-up (also known as dynamic backup) to replace any IAP unit thats out of service. In addition, each lane features a double camera system (two front-shot and two rear-shot cameras for each lane) and double video switch to guarantee a fully redundant IAP system.
Every CP is equipped with a double fully redundant charging point controller (CPC) that serves as a stand-by module for the primary CPC, since this represents the heart of the toll collection system in terms of roadside equipment. The backup CPC is the same kind of embedded system as the primary one and is equipped with the same peripherals.
Finally, in Tecsidels system, the software is designed and developed to support the hot back-up and load balancing of all subsystems.
Need to know?
System downtime is unacceptable in freeflow tolling, so complete redundancy is a must
> In free-flow tolling
applications vehicles do
not have to stop at toll
booths, which means
they must be accurately
identified while traveling
- there is simply no margin for error
> Creating a fully redundant solution involves tailoring software, hardware and the interaction between the two
Dual-concept tools play a key role in building fault-tolerant systems