It’s commonly assumed that the introduction of fleets of driverless taxis will help to reduce private car ownership, particularly in cities.
But a new simulation for the Swiss city of Zurich has come to a slightly different conclusion, suggesting that if automated private vehicles are also available, consumers might not only keep their vehicle, but find its convenience and flexibility so attractive that the overall number of kilometres driven might increase.
"If the fleet is too small, the service is not attractive to users"
The study, led by Professor Kay Axhausen of ETH Zurich’s Institute for Transport Planning and Systems, explored how the city’s traffic volume might change if automated taxis were to be introduced at some point over the next two decades.
The team found that offering a ridesharing service with automated vehicles would not reduce the number of private vehicles, and that automated transport might even increase the number of kilometres driven.
The researchers contrasted their findings with previous studies, such as those conducted in Singapore and Austin, Texas. The Singapore study found that with automated taxis available, total demand for mobility could be met with just a third of the current vehicle fleet. In the Austin study, researchers predicted that the city’s vehicle fleet could be reduced by as much as 90 percent.
ETH Zurich said previous simulations had assumed too high a demand for automated taxi services, without taking into account user preferences regarding flexibility, costs and waiting times.
“Previous simulations mostly assumed ideal conditions, such as that every road user opts for an automated taxi provided waiting times are below a certain level,” said Axhausen.
His team developed a simulation that takes into account supply and demand, as well as users’ individual patterns of behaviour. For a given fleet size, the simulation then generates a certain price per ride and a certain level of demand.
In the first scenario, the researchers supplemented the city’s existing transport system with a fleet of self-driving taxis. In a simulation with 150,000 agents representing 10 percent of Zurich road users, more than 60 percent of transport was achieved by “automated public transport” – including self-driving buses, rail and taxis. This scenario saw the share of motorised personal transport fall from 44 to 29 percent.
Axhausen’s team experimented with different fleet sizes and found that the ideal level of demand and price for Zurich would lie with a fleet of some 3,000 automated taxis. At this level, the price equated to about half a euro per kilometre driven – similar to the current per kilometre costs of a conventional private vehicle, but much lower than the cost of a conventional Zurich taxi.
“If the fleet is too small, the service is not attractive to users,” said Axhausen, “but if it’s too large, the service becomes too expensive and similarly unattractive.”
In the team’s second scenario, participants had the option to buy their own automated vehicle instead of sharing one. In this scenario, the overall number of cars per household remained almost unchanged.
“The combination of high flexibility and the chance to make good use of time spent in the vehicle makes this form of mobility very attractive – especially when all family members can use the vehicle,” said Axhausen.
This simulation also saw private driverless cars increase volume on the roads, with the virtual agents in the study travelling up to 250,000 extra kilometres per day in automated private vehicles.
The researchers believe that their findings require a reevaluation of automated urban transport. “Automated taxi fleets will initially remain relatively small due to costs alone, and the assumption that personal transport will give way to shared automated vehicles is incorrect,” said Axhausen.