The main characters in this series are little trucks that have different personalities. Little red is shy and lack of self confidence, little yellow is slow, little pink is timid and little black is cool. In each book, these little trucks are given a mission to achieve. During the process, they will face different kinds of obstacles and they will need to resolve them on their own. Usually they will have helped others along the way and improved their confidence.
这套书也是一贯的宫西达也风格，主人公是四辆性格各异的小卡车，有点害羞且不自信的小红，慢性子的小黄，胆子很小的小粉，还有急性子爱耍酷的小黑。每本书中，小卡车都会接到一项送货任务。在完成任务的旅程中，小卡车们遇到了各种各样的困难，需要他们不断地想办法去解决。最终，它们都圆满的完成了任务，并且在完成任务的过程中还帮助了他人，也增加了自信，锻炼了胆量。
除了四辆小卡车外，书中还画了很多其他交通工具，警车，消防车，垃圾车，拖车，吊车，水泥搅拌车，道路清障车，道路救援车，还有飞机和轮船等等。这些交通工具们也有他们各自的工作，他们也给小卡车们提供了各种帮助，而小卡车们也在旅途中帮助了他们。