## 1 Introduction  
As highlighted by [PERSON] and [PERSON] [1], \"in the transport policy literature, there is consensus that'sound' policies have to meet three criteria: they should be effective, efficient and fair\" [2]. Effectiveness and efficiency have received significant attention in the last decades [11], while the same does not apply to fairness except for contributions addressing social exclusion (e.g., ref. [3]). In recent years, the attention on transport fairness has increased thanks to the growing importance of inequality reduction at the international level, e.g., among the Sustainable Development Goals of the United Nations [4]. The lack of studies in this field is linked to the normative nature of fairness, making it difficult to measure and apply it to a cost-benefit analysis (one of the most diffused policy assessment tools [1, 5]). Due to this normative issue, most studies in transport fairness focus on distributional analyses, i.e., how transport effects (such as air pollution variations or safety variations) are distributed over people [1, 6]. One of the most addressed effects is the variation of _individual accessibility differences_[5]. Indeed, accessibility is one of the critical pillars for a sustainable mobility paradigm [7]. Its improvement is one of the core concerns for transportation ministries throughout the world [8]. However, most accessibility measures developed in the literature are not suitable to point out such individual differences since they focus on the physical separation among places and overlook the accessibility differences that could exist among people living in the same area (e.g., because of their different modal restrictions or daily schedules [9]). To fill this gap, so-called _person-based_ accessibility measures have been developed [10; 11]. Among them, the _Space-Time Accessibility_ measure (_STA_) is one of the most diffused given its sensitiveness to individual space-time constraints [12; 13; 14]. Although _STA_ is very suitable for investigating individual accessibility differences in general, its high complexity does not allow a clear understanding of the specific role the transport system plays in such differences, differences which are fed by a multitude of spatial, transport, individual and temporal factors. This is a relevant limit of _STA_ especially from the perspective of transport policy makers, who should introduce transport policies aimed at reducing such differences. Indeed, accessibility differences are often unavoidable and the transport system cannot remediate them [1]. For instance, inevitably, people living close to a large facility (e.g., a hospital) have better access to it than people living far away. However, this is unavoidable due to land-use constraints (hospitals cannot be built in any municipality), and transport policies cannot eliminate distance. Given this issue, it is necessary to complement _STA_ with transport performance measures (With the term \"transport performance\" we mean a set of transport indicators that describe the efficiency of the transport system, such as commercial speed, network capacity, service period, average waiting or transfer time, or monetary cost of travel) able to isolate the specific role of the transport system in individual accessibility differences, which could be avoided or remediated through transport policy interventions. For this purpose, this paper introduces a so-called _Space-Time Transport Performance_ measure (hereinafter _STTP_). The rest of the article is organised as follows. Section 2 reviews main place- and person-based accessibility measures used in literature and points out the elements that prevent _STA_ from isolating the role of the transport system in individual accessibility differences. On this basis, Section 3 introduces _STTP_ by describing its key features and its computation process. _STTP_ is then tested in Section 4 together with _STA_ to determine the complementary results that are achievable with the proposed measure. Moreover, it discusses the limits of _STTP_.