Ad hoc networks can be formed on highways among moving vehicles, each equipped with a wireless LAN device. However, during times of low traffic density, it is likely that such networks are disconnected. This paper tests the hypothesis that the motion of vehicles on a highway can contribute to successful message delivery, provided that messages can be relayed---stored temporarily at moving nodes while waiting for opportunities to be forwarded further. Using vehicle movement traces from a traffic microsimulator, we measure average message delivery time and find that it is shorter than when the messages are not relayed. We condclude that ad hoc relay wireless networks, based on wireless LAN technologies, have potential for many emerging applications of this kind