Theoretical evaluation of transport interventions: A case study of the Nottingham workplace parking levy

Theoretical approaches to evaluation provide a framework for understanding, testing and refining the assumed connections between an intervention and their anticipated impacts. This takes into account relevant exogenous contextual changes, as and when they occur, by considering how they will impact on the theory underlying the intervention and thus seeks to assess to what extent change is due to intervention rather than other factors. They provide an explanation as to why and how change has occurred. Such an approach is therefore particularly appropriate to initiatives which are complex and or innovative in nature or could be influenced by many variables. Theoretical Evaluation (TE) has been used for many social and health initiative evaluations, its application however, within the transport sector is relatively new, but is now included in guidance on transport evaluation by the UK government. The aim of this paper is to present the case study of the use of TE in relation to the Nottingham Workplace Parking Levy (WPL) and assess the suitability of TE as a tool for such evaluations. (The WPL is a levy on parking provided by employers. It acts as a transport demand management measure with the revenue hypothecated for funding wider transport improvements.) The paper introduces the WPL, and briefly reviews approaches to evaluation. The paper then focuses on the case study of the evaluation of the WPL using TE. The paper concludes, based on the literature and the case study, that a combination of two TE approaches, ‘Theory of Change’ and ‘Realistic Evaluation’, is an appropriate framework for evaluating complex transport interventions like the WPL. It shows this approach has been useful in the evaluation of the Nottingham WPL by identifying the level to which this scheme has achieved its objectives.