Our findings applying the rural-to-urban—transect method to trunk roads in Hamburg confirms common perceptions about urban structure in Europe: the decreasing density and rising motorization of residential areas towards the periphery, and also the rhythmic alteration of predominantly residential versus business-, leisure- and transport-related land uses along the transect. Some of these observations have been stated independently of transects or trunk roads (e.g. Bertaud 2018). As empirical foundations for the ‘rural to urban transect’ school of thought do not seem abundant in the academic literature, our and similar observations may constitute a valuable contribution.
The prototypical rural-to-urban transect, however, appears to lack detail and complex variation along roads or transport infrastructure in general and radial trunk roads in particular. In a similar vein, Tagliaventi (2016) suggests several amendments to the transect concept to use in Europe. He found, for instance, “the need to introduce an intermediate category to the transect classification to identify a common level of European urban settlement with neither the strength, size, nor mixed-use complexity of the neighbourhood” as defined in the Charter of the New Urbanism (Congress for the New Urbanism). Still, ‘neighbourhood’-like structures are clearly visible in our transect diagrams.
Turning towards the practical relevance of the method, we could show that it provides a good overview over the whole length of a trunk road and helps to identify special situations, e.g. ‘metro zones’ or ‘arrival cities’. The observation of transects might thus be helpful to identify all a city’s different spaces, even temporary or transitional ones, and appreciate them in due fashion (Düwel 2010). For instance, the diagrams are useful to identify urban structures resp. ‘neighbourhoods’ with a higher residential density where walk- and bikeability should be dominant design aspects. They also reveal spaces that may require intervention, e.g. strong variation in demographics along the transect and questionable combinations like a high share of residential land use around high traffic volumes. Bohmann and Siegmund (2013) provide a useful influence matrix to identify critical factors for the development of selected sections. Such issues, however, could also be studied on a grid or zoning basis. An advantage of the transect method is that it can be combined with other approaches to analyse road space that frequently use two-dimensional representations (e.g. Dutkowski 2012) to address a huge variety of issues around trunk roads.
In the context of urban mobility, our analysis highlights several issues that link to current issues discussed in urban town and transport planning. Quite prominent is the disparity of motorization and traffic volumes. As natural as this pattern may seem after taking local mobility options etc. into account, it becomes abundantly clear that downtown dwellers bear the fallout of mobility choices made in suburbia. An urban economist might, however, argue that residents along the transect chose this trade-off between adverse traffic effects and benefits of a more or less central location.
Another obvious pattern is the increasing share of households with children towards the periphery, documenting that the downtown areas are not a favoured place for families with children—an observation that warrants political discussions.
Further analysis could, on the one hand, widen the scope of parameters and look at different cities with different historic, economic or topographic backgrounds, incorporate more detailed data or focus on particular aspects—e.g. roadspace allocation, the accessible labour market, real estate prices, patterns in business and retail or local mobility patterns. The transect method has been found useful in other, e.g. anthropological contexts (Krebs and Pilz 2013). As Tagliaventi (2016) suggests to distinguish between different building types within the urban Transect Zones, it might be recommendable from a geographers point of view to analyse the urban morphology along a transect, classified by building, composition and neighbourhood typologies as documented in Schirmer and Axhausen (2015). Bertaud (2018) suggests a number of indicators to manage developments with relevance to urban planning, such as “rent-to-income ratio, floor consumption per capita, and median commuting time”, the latter corresponding to the accessible labour market.
On the other hand, comparing transect diagrams of the same trunk road for different points in time could be instructive to illustrate and explain the development of the urban fabric, for instance the deterioration or gentrification of certain areas, the relocation of production etc.
We conclude that transect style, two-dimensional analyses of roads and their surroundings in general are compelling where larger stretches of roads and their interaction with the surroundings are examined. They can help to illustrate historic and contemporary developments and to identify spaces worth closer examination. It should be noted that a two-dimensional approach cannot analyse or resolve issues arising from the larger urban environment.