I. Introduction
The development of the next generation networks push the researches of intelligent transportation. Vehicular ad hoc networks (VANETs) are the most considered network model for an intelligent transportation system. The decentralization, heterogeneity and nontrustworthiness of VANETs pose the challenges in secure message-transmission and transaction-execution [1], [2]. Advanced technologies such as cloud computing, smart chips, blockchain, etc., promote the development of VANETs [3], [4], [5]. Integrating blockchains with VANETs can provide solutions to some existing challenges. The establishment of VANETs can greatly promote breakthroughs in applications such as driverless and intelligent road rescue. Traffic safety and efficiency are constantly being optimized due to the extensive research of VANETs. The complex VANETs require the data transmission schemes to be extremely scalable. Hence, scalable computation is an important part of advancing VANETs technology. Furthermore, the increasing data scale of Internet of Things (IoT) and new trends in data applications have spurred the growing demand for scalable computation in new networks [6], [7]. In traffic networks, vehicles collect and upload their own attribute data or surrounding road condition information monitored by on-board units (OBUs) [8], [9]. Meanwhile, roadside infrastructure and remote servers can collect and analyze uploaded information. As a result, according to the analysis results, the traffic control center formulates the optimal traffic flow management strategy and emergency response method [10], [11].