As the capital of Baden-Württemberg, Stuttgart has about 600,000 inhabitants. Taking the entire metropolitan region into account, this number grows to 2.7 million and more than 1 million employees. Europe’s strongest region in terms of exports supports its strength through the automotive and mechanical engineering sectors. Companies such as Daimler and Porsche enjoy an excellent reputation worldwide. Several universities and numerous research institutions form together a diversified research landscape. Stuttgart is well-acquainted with its transport-related challenges, which result from high mobility demand from citizens and the economy. Nonetheless, the city is also working hard on solutions for urban mobility aimed at increasing quality of life and at reducing the negative impact of traffic on the environment.
CoEXist use cases in Stuttgart
Despite an excellent public transport system, a state-of-the-art traffic management center and cycling improvements, the city’s topography and the resulting network structure affect the reliability of the urban transport network. Congestion on the motorway can also influence traffic flow in the urban area.
For this reason, the city is eager to explore the impacts of CAVs on the road infrastructure and to what extent they can alleviate the traffic congestion in the city and its surroundings.
Impacts of CAVs on travel time and mode choice on a network level
The first use case of Stuttgart assumes that advanced CAVs will influence mode choice as cars become more comfortable and CAV users will experience various advantages including:
- shorter or more reliable travel times due to increased capacity,
- possibility to use in-vehicle time more efficiently,
- lower parking search, access and egress time with the introduction of valet parking.
The study assumes that once the CAV share of the traffic is higher than 50%, traffic flows are more seamless and the driver needs to be less engaged with the car. Thus, the perception of travel time is reducing by around 30%. This would have the following results.
- Highly automated vehicles may have a substantial impact on travel demand, thus the total distance traveled will increase in the long run.
- The model suggests that higher automation levels of CAVs increases the attractiveness of the car, which creates a modal shift from public transport
- If the perception of travel time is reduced and comfort is enhanced, users will take more and longer trips.
Overall, a possible rebound effect on travel demand may reduce positive impacts of CAV on capacity.
Impact of driverless car- and ridesharing services
In case CAVs are fully automated and enough ridesharing options are available, car-ownership becomes obsolete. Therefore, the City of Stuttgart is investigating the extent to which the introduction of fully automated ride- and car-sharing systems, capable of operating without drivers in the Stuttgart Region, can influence transport supply and travel demand.
The basic assumption is to have 100% CAVs capable of operating completely automated (and therefore driverless) within the Stuttgart Region. In this scenario, most of the car travellers would shift to ride-sharing services. As the potential for pooling is limited and as buses are replaced by smaller ridesharing vehicles, the kilometres travelled would decrease only slightly. However, the total number of vehicles needed to transport people could be substantially reduced, to only a quarter of the current number of vehicles, thus saving on space for parking and other types of activities.
The modal shift from public transport to independent ridesharing or carsharing depends on the price of the services and on car ownership levels. If the out-of-pocket costs for these services are approximately 50% higher than public transport and that car ownership remains at current levels.
- Ridesharing integrated into public transport can operate as a feeder service for traditional public transport and offer direct trips where public transport service quality is insufficient. Direct RS+ services provided at the cost of public transport gain a large modal trip share of around 25%. This leads to a total public transport share of 33% (baseline: 14%) and a reduced share for car modes of 41% (baseline: 54%).
- Assumptions on the willingness of people to give up their private vehicle and to share vehicles have a high impact on vehicle traffic. If half of the persons with access to a car relinquish their car, vehicle distance travelled will go down by approximately one quarter.
- The number of required vehicles can be reduced, if ridesharing is integrated into public transport (RS+) and carsharing is available. In this case, up to 25% of all vehicles can be omitted. This number can be further reduced with an increasing willingness to share.