  With the emergence of communication services with stringent requirements such
as autonomous driving or on-flight Internet, the sixth-generation (6G) wireless
network is envisaged to become an enabling technology for future transportation
systems. In this paper, two ways of interactions between 6G networks and
transportation are extensively investigated. On one hand, the new usage
scenarios and capabilities of 6G over existing cellular networks are firstly
highlighted. Then, its potential in seamless and ubiquitous connectivity across
the heterogeneous space-air-ground transportation systems is demonstrated,
where railways, airplanes, high-altitude platforms and satellites are
investigated. On the other hand, we reveal that the introduction of 6G
guarantees a more intelligent, efficient and secure transportation system.
Specifically, technical analysis on how 6G can empower future transportation is
provided, based on the latest research and standardization progresses in
localization, integrated sensing and communications, and security. The
technical challenges and insights for a road ahead are also summarized for
possible inspirations on 6G enabled advanced transportation.
