Modal split

The term modal split keeps cropping up in debates about the transport transition. Read here to find out what it can achieve and where caution is required.

The term modal split crops up time and again in debates about the transport transition. For example, some municipalities set themselves targets in the transport sector that are defined by a change in the composition of the modal split. For example, they call for a reduction in the modal split for motorized traffic or set targets for the percentage share of non-motorized traffic in the total traffic volume. This is because the modal split can be a tool for describing the composition of traffic and thus also for determining how this changes over time. Or how it should change in the future. On the other hand, however, it is subject to certain limitations that need to be taken into account when interpreting it.

But let’s start at the very beginning. What exactly is the modal split? It is a parameter that reflects the share of individual modes of transport in the total number of kilometers traveled or trips made per day. In other words, it describes the percentage distribution of the transport volume between different modes of transport. When determining the modal split, passenger transport and freight transport are considered separately. And the respective transport performance is determined accordingly using different transport parameters. For freight transport, the transport performance is given in tonne-kilometres (tkm). For passenger transport, on the other hand, it is expressed in passenger kilometers (pkm). The distance travelled (mileage) and the number of passengers or tons transported (volume) are multiplied together. However, it is also possible to determine the modal split for all trips. In this case, the share of the individual modes of transport in the journeys made is determined, but not the length of the individual journeys.

In Germany, the data for the modal split is collected by the Federal Ministry of Transport. It publishes the “Transport in Figures” report once a year, which also includes the transport performance and market share for the individual modes of transport. In the current report from September 2022, the transport performance for 2021 for MIT, for example, is 86.8 percent. By contrast, local public transport accounts for 13.2 percent, of which 7.6 percent can be attributed to local public transport. The Federal Ministry for Digital and Transport also publishes statistics on the modal split of passenger transport, including non-motorized transport. This also includes data on cycling and walking.

So far so good. However, the modal split figures are not as easy to interpret as they seem. It is also hardly possible to compare individual municipalities. This is due to a number of aspects that come together. On the one hand, there is a risk in the different types and timing of data collection. According to transport scientist Martin Randelhoff, data from different municipalities is only comparable to a limited extent, depending on the sampling and survey techniques, definitions, the layout of the survey areas and other methodological differences. Furthermore, the modal split calculated on the basis of journeys in particular creates a distorted picture of transport reality. This is because it only determines the journey as a change in location from one point to another, without specifying the actual distance. This method overestimates the percentage of journeys made on foot or by bike, as although these are many, they are often only short journeys. Measured in passenger kilometers, they make up a much smaller proportion of the total traffic volume.

In the worst-case scenario, for example, a statistical decrease in the proportion of trips made by private cars can be recorded, even though there has been an increase in car mileage. When looking at the data, it is therefore important to consider exactly how it is recorded. Another point that influences the informative value is the definition of the types of traffic flows to be recorded. A distinction is made between journeys within the urban area (internal traffic) and through traffic from the surrounding area. The modal split of the individual traffic flows can vary greatly depending on the definition. If, for example, commuters or visitors from the surrounding area are also included, the share of motorized private transport often increases significantly.

In general, it is also important to always classify the data in the context of the absolute figures. A general increase or decrease in total traffic volume, for example, also leads to an increase or decrease for the individual means of transport. It is also necessary to look at developments in society as a whole in order to interpret the data. This was observed during the coronavirus pandemic, for example. The external circumstances led to an increase in the use of cars, cycling and walking, while the use of public transport decreased. The development of the modal split over the years cannot therefore be seen in isolation from current circumstances.

Despite all the hurdles, the modal split is a good tool for recognizing changes in the composition of traffic. However, it must be interpreted correctly. To do this, it is essential to consider not only relative modal split values, but also the absolute values on which the calculation is based and to familiarize oneself with the methods used to record them. By taking a detailed look, however, exciting developments can be identified. And it is precisely the classification of the data and the search for the causes of certain trends that can ultimately also be helpful in urban and transport planning.

You can find more exciting statistical knowledge about traffic here.