  The highway vehicular ad hoc networks, where vehicles are wirelessly
inter-connected, rely on the multi-hop transmissions for end-to-end
communications. This, however, is severely challenged by the unreliable
wireless connections, signal attenuation and channel contentions in the dynamic
vehicular environment. To overcome the network dynamics, selecting appropriate
relays for end-to-end connections is important. Different from the previous
efforts (\emph{e.g.}, clustering and cooperative downloading), this paper
explores the existence of stable vehicles and propose building a stable
multi-hop transmission backbone network in the highway vehicular ad hoc
network. Our work is composed of three parts. Firstly, by analyzing the
real-world vehicle traffic traces, we observe that the large-size vehicles,
\emph{e.g.}, trucks, are typically stable with low variations of mobility and
stable channel condition of low signal attenuation; this makes their
inter-connections stable in both connection time and transmission rate.
Secondly, by exploring the stable vehicles, we propose a distributed protocol
to build a multi-hop backbone link for end-to-end transmissions, accordingly
forming a two-tier network architecture in highway vehicular ad hoc networks.
Lastly, to show the resulting data performance, we develop a queueing analysis
model to evaluate the end-to-end transmission delay and throughput.
  Using extensive simulations, we show that the proposed transmission backbone
can significantly improve the reliability of multi-hop data transmissions with
higher throughput, less transmission interruptions and end-to-end delay.
