Promoting urban carpooling: a total social cost approach based on the Lyon case study

This paper investigates the impacts of several implementations of daily mobility policies and external shocks on social costs, with a particular focus on carpooling. This social cost is calculated considering consumer's cost, external costs, as well as the expenses and incomes of public authorities and private companies. Four transport modes are considered: solo driver, carpool driver, carpool passenger and public transport. A modal choice model is then applied to trips with 6,287 different origin-destination of the eastern Lyon area. Simulations of time-gain and monetary scenarios are then realized to observe impacts on demand and consequently on the other parameters affecting the social costs. Our results show that consumer's costs explain the majority of the total social cost. Values commonly used for externalities barely impact the social cost in the simulations and traffic reduction measures impact more public and private revenues than they reduce externalities, leading to higher total social costs. Moreover, results illustrate significant variations at the geographical scale, depending on the ODs where the policies are applied. These results suggest implementing daily-carpooling incentives should be decided conscientiously considering the local context.