  Tradable mobility credit (TMC) schemes are an approach to travel demand
management that have received significant attention in the transportation
domain in recent years as a promising means to mitigate the adverse
environmental, economic and social effects of urban traffic congestion. In TMC
schemes, a regulator provides an initial endowment of mobility credits (or
tokens) to all potential travelers. In order to use the transportation system,
travelers need to spend a certain amount of tokens (tariff) that could vary
with their choice of mode, route, departure time etc. The tokens can be bought
and sold in a market that is managed by and operated by a regulator at a price
that is dynamically determined by the demand and supply of tokens. This paper
proposes and analyzes alternative market models for a TMC system (focusing on
market design aspects such as allocation/expiration of credits, rules governing
trading, transaction costs, regulator intervention, price dynamics), and
develops a methodology to explicitly model the disaggregate behavior of
individuals within the market. Extensive simulation experiments are conducted
within a departure time context for the morning commute problem to compare the
performance of the alternative designs relative to congestion pricing and a no
control scenario. The simulation experiments employ a day to day assignment
framework wherein transportation demand is modeled using a logit-mixture model
and supply is modeled using a standard bottleneck model. The paper addresses a
growing and imminent need to develop methodologies to realistically model TMCs
that are suited for real-world deployments and can help us better understand
the performance of these systems and the impact in particular, of market
dynamics.
