The need to improve the sustainability of daily mobility in urban areas has been high on the political agenda worldwide. One major concern has been that of the growing car dependency. The growing distance between the activities human carry out has naturally been at the root of such phenomena. Efficient transport systems and high travel speeds have enabled access to ever distant opportunities. On the flip side, such conditions have reduced the need for proximity, which in turn has led to a distancing between human activities and to greater car dependency.

For this paper we built a theoretical framework that hypothesises the existence of a negative feedback loop between local and regional accessibility (illustrated above). We then provide initial empirical research into the feedback loop. We explore how high regional accessibility has contributed to losses in local accessibility by enabling concentration of population in local low accessibility environments (one of the two explanatory phenomena behind the negative feedback). Our research uses a 2-step approach to, first, reveal the spatial relationship between local and regional accessibility levels, and then to explore the influence of urban development periods on such relationship. We use a European metropolitan context for this exploratory research (the metropolitan area of Porto), making use of a cross-sectional database on local and regional accessibility levels, supported by longitudinal data on population distribution and building age, both at a high spatial detail level. Local and regional accessibility levels are assessed for 15-min travel distance by foot and by car, respectively.

In the absence of longitudinal data on accessibility levels, it was not possible to directly observe the hypothesised feedback cycle. Nevertheless, we found evidence of two necessary, though insufficient, conditions of said cycle. In line with the hypotheses, we found significant amounts of the population living in high regional and low local accessibility contexts (around 17%). We also found evidence of higher concentration of recent urban development in areas offering low local and high regional accessibility levels, in comparison to their high local accessibility counterparts. Indeed, these areas show significant population growth, growing at a faster rate than their high local accessibility counterparts. These findings encourage further research into the hypothesised feedback loop.

提高城市地区日常出行可持续性的必要性一直是全球政治议程的重点。一个主要的担忧是对汽车的日益依赖。人类进行的活动之间的距离越来越远自然是这种现象的根源。高效的交通系统和高速行驶使我们能够获得遥远的机会。另一方面，这种情况减少了对接近的需求，这反过来又导致人类活动之间的距离和对汽车的更大依赖。

对于本文，我们建立了一个理论框架，假设本地和区域可访问性之间存在负反馈循环（如上图所示）。然后，我们对反馈循环进行初步的实证研究。我们通过使人口集中在当地的低可达性环境中（负反馈背后的两个解释现象之一）来探索高区域可达性如何导致当地可达性的损失。我们的研究采用两步法，首先揭示地方和区域可达性水平之间的空间关系，然后探讨城市发展时期对这种关系的影响。我们使用欧洲大都市背景进行这项探索性研究（波尔图大都市地区），利用关于地方和区域可达性水平的横截面数据库，并得到关于人口分布和建筑年龄的纵向数据的支持，两者都具有高度的空间细节水平。当地和区域的可达性水平分别针对步行和驾车 15 分钟的旅行距离进行评估。

在缺乏可访问性水平的纵向数据的情况下，不可能直接观察假设的反馈周期。然而，我们发现了上述循环的两个必要但不充分的条件的证据。与假设一致，我们发现大量人口生活在高区域和低地方可及性环境中（约 17%）。我们还发现，与当地高可达性对应的地区相比，近期城市发展集中在当地和高地区可达性水平较低的地区。事实上，这些地区显示出显着的人口增长，其增长速度比当地高可达性地区的增长速度更快。这些发现鼓励进一步研究假设的反馈循环。