As road management policies develop, the technical requirements for tolling become more sophisticated. This article examines how to combine conventional loop detector technology with state-of-the-art software, to meet this challenge. The financial viability of a design-build-finance-operate (DBFO) road scheme, funded by shadow tolling, for its public and private partners depends entirely on the accuracy of its traffic data acquisition. Traffic data collection for shadow tolling does not require the complex equipment and systems of the toll plaza, or the infrastructure usually associated with tolling. Data collection can be conducted normally in free-flowing traffic, and made transparent to road users. The authors argue that loop detectors alone cannot be sufficiently accurate, but that they can become sufficiently accurate with some roadside assistance. This belief is based on experience with Atkins IDRIS outstations, each of which combines a group of commercially available loop detectors with some clever processing of their output, to give a count accuracy exceeding 0.05%. The IDRIS outstation algorithm contains about six tests, each addressing a specific criterion, which evaluate detector output. The outstations can become key components of a shadow tolling system, and also belong to an incident detection system.
Abstract