  The real-time traffic monitoring is a fundamental mission in a smart city to
understand traffic conditions and avoid dangerous incidents. In this paper, we
propose a reliable and efficient traffic monitoring system that integrates
blockchain and the Internet of vehicles technologies effectively. It can
crowdsource its tasks of traffic information collection to vehicles that run on
the road instead of installing cameras in every corner. First, we design a
lightweight blockchain-based information trading framework to model the
interactions between traffic administration and vehicles. It guarantees
reliability, efficiency, and security during executing trading. Second, we
define the utility functions for the entities in this system and come up with a
budgeted auction mechanism that motivates vehicles to undertake the collection
tasks actively. In our algorithm, it not only ensures that the total payment to
the selected vehicles does not exceed a given budget, but also maintains the
truthfulness of auction process that avoids some vehicles to offer unreal bids
for getting greater utilities. Finally, we conduct a group of numerical
simulations to evaluate the reliability of our trading framework and
performance of our algorithms, whose results demonstrate their correctness and
efficiency perfectly.
