Developing a contactless bankcard fare engine for Transport for London

Abstract

This thesis investigates the design of a fare engine which operates within the constraints of using contactless bankcards as a fare instrument, while satisfying the complex current and future fare requirements of Transport for London (TfL). A fare engine is a system which transforms user transactions at fare gates and validators into chargeable fares. Contactless bankcard fare payment differs from current fare smartcard systems by requiring a centralized fare engine. The proposed fare engine utilizes a data structure which maintains each user's journey history in three successive tiers of linked objects. This structure enables transactions to be correctly sequenced without a guarantee of in-order arrival of gate and validator transactions. A cleanup routine prevents the data structure from growing without bound as journey history accumulates. A dynamic journey linking mechanism allows the effect of inserted transactions to be propagated throughout the data structure and reflected in the affected journeys with near-constant time complexity. This ensures scalability while providing real-time feedback for customer service and payment authorization needs. A solution is devised for the coupling of arbitrary origin-destination fares with zonal period tickets. The paradigm of automatic ticket selection is introduced, overcoming the limitations of the existing capping algorithm used by TfL. Through the tracking of parallel fare scenarios, passengers are guaranteed a total fare no higher than if they had purchased the optimal period ticket for their usage profile. With the solutions proposed in this thesis, a contactless bankcard fare engine for TfL appears feasible.