My recent visit in Stuttgart has inspired me to take a closer look at the challenges that the city’s public transport network is facing. As a public transport consultant, I think the main issue is increasing the modal share of Stuttgart’s public transport. A relatively low modal share negatively impacts the quality of life in Stuttgart, including e.g. air pollution levels, as seen recently in the particulate matter (Feinstaub) alert.

I see the following actions as necessary for a higher public transport’s modal share:

1. Public transport fare review
2. Car park fees management plan
3. Bus network optimisation

Low modal share

According to the local transport plan for Stuttgart (link), in 2010 33.1% of all motorised journeys within the city were taken by public transport. While the annual traffic survey suggests that some improvement has been made since then, the table below shows that public transport in Stuttgart is in a worse position than in other German cities:

City	Public transport’s modal share
Frankfurt	40.5%
Hanover	37.2%
Dusseldorf	36.9%
Stuttgart	33.1%

In particular, the component of internal journeys (i.e. starting and ending within the city limits) with 37% share stands out. Typically, this component is the main driver of a strong overall modal share and it is above 50% for some peers. The main reason for that is a naturally good public transport offer in the core city, where frequency and accessibility are satisfactory for the majority of potential passengers. As a result, the relative attractiveness of a private car for short journeys through congested streets is low.

The above is most definitely the case for Stuttgart, with a dense tram (Stadtbahn) network within the city limits, supported by highly-integrated buses. Yet the modal share is barely above 1/3 of motorised journeys and not expected to reach 40% even by 2025 (the transport plan’s projection is 39% for 2025).

Causes

I have identified the following drivers of low modal share in Stuttgart:

• Public transport fare level and structure. Annual fare adjustments resulted in an aggregated increase by 24.6% between 2007 and 2015, despite aggregated inflation at less than half of that figure (11.4%) over the same period. As a result, passengers may feel they are asked to pay more without justification, e.g. the quality of service is perceived as unchanged.

Additionally, diesel price fell by nearly 20% between 2012 and 2015, while fares went up by 9% at the same time. This divergence created a strong incentive to select private cars as a preferred mode of transport, against the long-term goals of sustainable transport.

• City centre car park offer. High availability and relatively low cost of parking spaces in the city centre are typical reasons for selecting the car over public transport. Both availability and cost need to be carefully adjusted in order to reverse the modal choices, in line with the principles stated in the Transport Development Plan (Verkehrsentwicklungskonzept) 2030: multi-storey car parks more expensive than public transport, on-street parking more expensive than multi-storey car parks (link).

• Public transport offer in suburban locations not served by trains (S-Bahn) or trams (Stadtbahn). Passengers from such places usually have to rely on buses and the level of their integration with rail-based means of transport. In a scenario where bus frequency or a choice of directions are deemed unsatisfactory, combined with fare level and car park availability (as per above), a direct journey by car may appear much more attractive than a combined bus + train + tram journey, despite convenient interchanges.

Negative impact

Low modal share of public transport is one of the reasons for a relatively high level of air pollution in Stuttgart. A recent particulate matter (Feinstaub) alert has shown both the risks to population’s health as well as the threat to the city government due to a breach of EU regulations (link).

Additionally, unsustainable modal split results in an increased financial burden for the city of Stuttgart. The subsidy for public transport has been increasing every year since 2011 (by 17%, i.e. €44m in total), despite regular fare increases and improving cost coverage ratio.

Next steps

In my view, the following steps would need to be carried out in order to support the modal shift in Stuttgart:

• Public transport fare review. With experience in financial modelling, one could estimate the level of fares that would attract more passengers with total income unchanged (using a constrained optimisation tool).

• Car park fee management plan. This would include a step-by-step guide to moving the incentive from car use to public transport use, balancing the positive and negative actions towards car users (e.g. reduce provision of on-street parking and offer special reduced fares for new passengers at the same time).

• Bus network optimisation. An optimised network can deliver better service (e.g. higher frequency, better reliability) without a need to purchase new vehicles by realigning the bus routes: reducing duplication, using shorter, straighter (including tangent) and faster routes.

Details of an alternative bus network in the city centre are shown here. This includes an additional shuttle bus to P+R Wasen using the existing fleet and saving up to €6m on vehicle purchase and operational costs.