Do want to use Linux on the road? Here is (a yet incomplete list) of free resources about Linux usage for cars, trucks and automobiles. See here for free navigation and GPS resources and for free resources for bicycles.
GNUnilink(http://gnunilink.sourceforge.net/) is a PIC adaptor that emulates a Sony Auto CD Multichanger, enabling the AUX input on the rear of suitable Sony car radios. This in turns allows the owner of such a radio to use these inputs for a portable CD or MP3 player. GNUnilink contains an optional serial link between PIC and PC. Button presses can be sent to the PC. The PC can set disk/track numbers/names and provide a real-time counter.
nissaneculibrary(http://staff.scm.uws.edu.au/~luke/software/CONSULT/) allows the user to get realtime sensor data from their compatible Nissan car (90-96 300ZX, Silvia, 180SX, Skyline GTR, GTS, or Nissan with CONSULT plug). The user can also temporarily modify timing and fuel injection, and perform active tests on various systems, relays, and solenoids. It is useful for diagnosing problems with your vehicle.
The DashPC(http://www.dashpc.com/) car multimedia system is a UI for automobile multimedia implemented in Linux. Its provides a comprehensive interface for MP3, DVD, and CD playback, a radio card interface, and GPS navigation. It features an easy-to-use interface and a modular design. Its functionality is configurable and the system is expandable with the use of plug-ins, which currently include plug-ins for controlling video4linux supported radio cards, viewing images, and running external commands.
pyOBD(http://www.obdtester.com/pyobd) is an OBD-II compliant car diagnostic tool. It is designed to interface with low-cost ELM 32x OBD-II diagnostic interfaces such as ELM-USB. It will basically allow you to talk to your car's ECU, display fault codes, display measured values, read status tests, etc. All cars made since 1996 (in the US) or 2001 (in the EU) must be OBD-II compliant, i.e. they should work with pyOBD.