A dual mode transponder for engaging in RF communications with a roadside
reader from a vehicle. The transponder includes an antenna, an electronic
toll collection (ETC) component, and an external interface. The ETC
component implements a pre-defined ETC communications protocol to detect
and interpret received signals and generate response signals when
operating in an ETC mode. The ETC component also includes a bypass port.
The external interface is coupled to the bypass port and has an external
port for receiving input signals. The ETC component includes a bypass
module for receiving a bypass instruction and entering a bypass mode. In
the bypass mode the ETC component refrains from implementing the ETC
communications protocol. Instead, the ETC component transmits the input
signals relayed from the external interface to the ETC component to the
reader.