The theoretical roots of accessibility reach back to Walter Hansen’s 1959 article on how accessibility shapes land use, and the concept has since been refined by scholars across transport engineering, geography, planning, and the social sciences. Engineers tend to frame accessibility as the cost of using a transport system, geographers emphasize the friction of distance, and social scientists focus on the interplay between transport systems and social processes. A widely cited multidimensional definition by Geurs and van Wee identifies four components: land-use patterns, the transport system, temporal constraints, and individual attributes. What has often been lost in German-speaking research, the authors argue, is the normative question of whether the resulting patterns are fair.

Karel Martens, whose work on transport justice anchors much of the international debate, offers a decisive shift in perspective. Accessibility, he suggests, can be measured either from the standpoint of destinations, asking how many people a facility serves, or from the standpoint of people, asking which facilities an individual can actually reach. For justice-oriented planning, only the second view matters, because what counts is equitable participation in social life rather than the catchment potential of infrastructure. A person’s accessibility depends not only on transport networks and land use but also on income, gender, vehicle availability, place of residence, household composition, and physical ability. This definition stands in deliberate contrast to planning built around potential car mobility, which presumes a freedom of choice that many people simply do not have.

The study grounds this argument in the philosophical tradition of distributive justice. Drawing on John Rawls’s theory of justice, scholars such as Martens and Rafael Pereira have argued that inequalities in accessibility are only acceptable if they benefit the least advantaged members of society. Martens extends Michael Walzer’s idea of separate spheres of justice to the transport sector, proposing that access to mobility should be decoupled from purchasing power in the same way that education and health care are. He pairs Rawls’s maximin rule, which demands that the situation of the worst-off be maximally improved, with a maximax rule requiring that the gap between the best- and worst-served groups not become too wide. A transport system, in Martens’s formulation, is fair if and only if it provides a sufficient level of accessibility to all under most circumstances.

Empirical studies show what happens when these principles are ignored. Research on planning processes in Boston and Miami documented by Kate Lowe reveals how efficiency-driven investment deepens inequality: in Miami, objections from minority representatives that the disadvantaged north of the region needed rail connections were set aside because extending the existing airport link served more passengers at lower cost. Justice-oriented planning, by contrast, means treating all residents as fundamentally equal, analyzing accessibility in socially differentiated ways, attending to affordability, and involving civil society groups from marginalized communities. It also means establishing robust minimum standards so that already strong corridors are not endlessly upgraded while poorly served areas are bypassed.

The second theoretical pillar, mobility justice, shifts attention from the transport system itself to the social production of unequal movement. Building on the new mobilities paradigm associated with John Urry and Mimi Sheller, this perspective treats mobility as emerging from a tension between movement and stillness, in which queues, checkpoints, fare barriers, and access restrictions distribute the capacity to move unevenly across social groups. Sheller identifies several mechanisms that produce these uneven mobilities: infrastructures that grant privileged groups fast, comfortable, and safe travel while exposing marginalized groups to slow and risky forms; control regimes operating through policing and pricing; and large-scale mobility regimes that reproduce classed, racialized, gendered, and age-based exclusions. In rural Germany, the dominance of the private car functions as exactly such a regime, undermining the viability of public transport on which a substantial share of the population depends.

The authors connect these theories to the German planning principle of Daseinsvorsorge, or public services of general interest, which covers everything from water and energy supply to health, education, and mobility. Transport infrastructure occupies a special position because it enables access to all other services. Yet the study identifies a critical legal and organizational gap: public transport is a voluntary task for most German municipalities, so service quality tracks local budgets rather than any binding standard. There is no subjective right to public transport provision, and local transport plans are not legally enforceable. Rural regions with weak finances therefore enter a downward spiral in which declining services push residents toward car dependency, which in turn further erodes the case for transit investment. As one cited analysis puts it, rural areas are not inherently car-dependent; political frameworks make them so.

The scale of the problem is substantial. Depending on regional structure, between 10 and 20 percent of adults in rural Germany have no access to a car, with far higher shares among young people and the elderly, and roughly 7 percent of residents of sparsely populated areas own a car they cannot really afford, a phenomenon known as forced car ownership. Rising urban rents are simultaneously displacing low-income, transit-dependent households from well-connected cities to peripheral areas. The authors argue that justice-oriented planning should focus precisely on these groups, using fine-grained accessibility analyses on small grid cells to identify disadvantaged households that administrative-level statistics overlook, and combining quantitative modeling with qualitative methods that capture discrimination and perceived accessibility.

The study also applies its framework to contemporary planning ideals, most prominently the 15-minute city championed by Carlos Moreno and implemented in Paris. While the concept promises socially and ecologically sustainable proximity, the authors note that walkable access to daily needs is, in a country shaped by decades of suburbanization, a privilege of urban populations. They therefore endorse the complementary vision of a 30-minute region, developed by Stefan Siedentop and Christian Gerten, which extends the idea to rural areas through expanded public transport rather than private automobility. Transport justice supplies the argument for financing such a system collectively, potentially through a levy that replaces fare revenue, echoing the experience of Germany’s short-lived 9-euro ticket, while mobility justice demands that barriers, affordability, safety, and freedom from discrimination be addressed so that a dense network alone does not reproduce exclusion.

The conclusions point toward concrete reform. The principle of Daseinsvorsorge must be specified through legally binding minimum accessibility standards, as already practiced in Austria and Switzerland through transit quality classes, and public transport should be elevated to a mandatory municipal task with corresponding funding. The authors note that although public transport generates economic benefits exceeding its costs, improves social participation, and contributes to climate protection, public debate fixates on its subsidies while ignoring the costs of road infrastructure. Ultimately, they argue, accessibility should be planned around participation in social life rather than the economic viability of alternatives to the car, with resources deliberately redistributed toward groups with low network capital. Which measures follow, the researchers acknowledge, remains a decision for policymakers, but the theoretical foundation for judging whether a transport system is just is now firmly on the table.

Subject of Research: Transport and mobility justice as a theoretical foundation for accessibility analysis in rural Germany

Article Title: Verkehrs- und Mobilitätsgerechtigkeit als theoretisch-konzeptionelle Grundlage für die Analyse von Erreichbarkeiten

Article References: Ahlmeyer, F., & Groth, S. (2026). Verkehrs- und Mobilitätsgerechtigkeit als theoretisch-konzeptionelle Grundlage für die Analyse von Erreichbarkeiten. Geographica Helvetica, 81(4), 567-587. https://doi.org/10.5194/gh-81-567-2026

Image Credits: AI Generated

DOI: 10.5194/gh-81-567-2026

Keywords: transport justice, mobility justice, accessibility, rural mobility, public transport, Daseinsvorsorge, spatial justice, transport poverty, 15-minute city, 30-minute region, transport planning, social exclusion

The problem stems from a rule that shapes nearly every residential street in Tehran. Current regulations allow a building to occupy 60 percent of a plot’s length plus two meters of frontage, with the structure placed at the northern edge of the land. On a standard 12-by-20-meter parcel, this translates into roughly 70 percent site coverage, leaving less than a third of the land open. Combined with permitted floor area ratios that the study calculated at 4.36, a figure the author describes as high density, the result is a fabric of six-story buildings, about 21 meters tall, packed into rows with as little as six meters separating them across their rear courtyards.

At Tehran’s latitude, that geometry collides catastrophically with the winter sun. The study calculated that the sun’s altitude at noon on the winter solstice is just 30.8 degrees, which means every meter of building height casts a shadow 1.67 meters long. A 21-meter building therefore throws a shadow roughly 35 meters across the ground, more than three times the width of a typical 12-meter residential street and more than double the combined length of the street and a six-meter courtyard. Because the regulations place every building at the north of its plot, the northern properties shade the courtyards and lower floors of the southern properties across the street almost continuously through winter, while southern buildings cast shadows across the full width of neighboring courtyards.

The consequences are stark in the numbers. In the existing condition, southern buildings receive about 271 kilowatt-hours of solar energy per square meter of facade annually, while northern buildings receive 336.6 kilowatt-hours per square meter, a gap of 24.19 percent. Roughly half of the southern facade on the lower floors falls into the minimum radiation category, shown in blue in the simulation outputs. The courtyards of southern properties receive direct sun on a strip only 1.4 meters deep for a single day each year. A ground-floor observer in a southern building faces a 21-meter wall just six meters away, an environment the author likens to standing in a concrete well.

To test whether this outcome was inevitable, the researcher built a digital model of a residential block: four rows of ten six-story buildings, forty structures in total, separated by a 12-meter passage, with dimensions matching the most common parcels in the city. The block was modeled in Rhino, with climate data from Mehrabad International Airport fed into the Grasshopper plugin and solar radiation analysis performed with Ladybug Tools. In parallel, the author produced manual scale drawings of shadow geometry at the summer and winter solstices, using the formula L equals H times the cotangent of the solar altitude angle. The two methods agreed precisely: the computer simulations reproduced the same shadow patterns as the hand calculations, with sunlight reaching only the sixth floor of southern buildings at winter noon.

Eight scenarios were then drafted, varying the position of the building footprint on the plot and the construction coverage while holding land dimensions, floor counts, and street width constant. Three emerged as clear improvements. In the most striking of them, Scenario 4, the northern buildings were simply moved from the rear of their plots to the street frontage, mirroring the southern buildings. Nothing else changed: same density, same footprint, same number of floors. Yet the energy received by southern buildings jumped by 19.2 percent, and the imbalance between the two sides of the street shrank from 24.19 percent to just 5.1 percent. In the best-performing variant, even at the winter solstice only the ground floor, typically a lobby or parking level, remained in shadow.

Two further scenarios achieved similar balance by trimming the footprint. Reducing coverage to 60 percent with a one-meter front courtyard, or to 50 percent with a one-meter setback on each side, pushed usable daylight deeper into the lower floors and allowed sunlight to penetrate the depth of the urban fabric even in winter. The lateral spacing between buildings also carries benefits beyond light: it reduces excavation risks between adjacent properties, improves safety during earthquakes and fires, and creates a porous fabric that lets wind circulate through the city rather than being blocked by continuous east-west rows. In Scenario 8, the floor area ratio dropped to 3, which the study identifies as an optimal level, and the energy gap between southern and northern buildings narrowed to 7 percent.

One counterintuitive finding deserves attention. In the scenarios with smaller footprints, the average annual solar energy per square meter of building surface actually decreased, falling from 336.6 to 279.9 kilowatt-hours per square meter for northern properties. This is not because the buildings receive less light; it is because they present less surface to collect it. Roofs, which receive the maximum solar energy, shrink along with the footprint, as does the crucial south-facing facade. The study emphasizes that energy comparisons are only meaningful between buildings with the same area, floors, and geometry, and that the redistribution of light across facades matters more than the per-square-meter average.

The findings arrive amid growing international recognition that solar access is a planning right, not a luxury. Sweden requires at least five hours of direct sunlight in living spaces between 9 a.m. and 5 p.m. on the equinoxes, and South Korea mandates more than two consecutive hours of daylight for each residential unit at the winter solstice, with offset distances calculated from building height and shading. Research cited in the study links daylight to circadian rhythm regulation, mental health, and resident satisfaction, while dense urban fabrics are associated with heat islands, poor ventilation, and elevated energy use for artificial lighting. Tehran’s own top-down, product-oriented planning tradition, the author notes, has left daylight, sunny hours, and shadow length largely unexamined in the design process.

The practical implications are unusually actionable. The single most effective intervention, relocating northern buildings to the street edge, costs nothing in density or floor space and could be written into siting regulations, though the author cautions that privacy, streetscape, and constructability need further study before implementation. Ground floors, which remain poorly lit in every scenario, are best reserved for parking and lobbies rather than living space. Plots of 12 by 20 meters, the study concludes, are simply too small to sustain a floor area ratio above 3 without critical shading, and larger parcel dimensions, or consolidation into towers on shared land, offer alternative paths, each with trade-offs in ownership, cost, and lived experience. Because even a one-meter lateral setback adds 30 square meters of sun-exposed surface per building, amounting to millions of square meters across the city, the study argues that the smallest regulatory changes carry enormous consequences, and should therefore be tested in limited neighborhoods, evaluated with resident feedback over successive years, and only then rolled out across the urban fabric.

Subject of Research: The effects of building density and placement on shading and solar energy reception in Tehran's residential neighborhoods

Article Title: Analyzing the effects of building density and placement on shading and solar energy reception in residential areas

Article References: Analyzing the effects of building density and placement on shading and solar energy reception in residential areas. (n.d.). https://doi.org/10.1007/s44327-026-00355-4

Image Credits: AI Generated

DOI: 10.1007/s44327-026-00355-4

Keywords: urban density, building shading, solar energy, daylight access, Tehran, urban planning regulations, building footprint, Ladybug Tools, winter solstice, floor area ratio, residential morphology, spatial justice