In the light of recent CERN LHA experimental data, we can now answer this with confidence in the following way:
Assuming that the Higgs boson is the new particle that has indeed been observed in the LHC:
1) In a car you cannot travel at the speed of light because a car and you have a non-zero rest-mass which means it must communicate with the Higgs field, and that causes you to ALWAYS travel less than the speed of light.
2) The speed of light is the same for all observers no matter how fast they are travelling relative to some other moving object. The reason for this is that photons NEVER interact with the Higgs field. i.e. they not only have zero rest-mass, they MUST travel at the speed of light. (And so must every other massless particle).
These two statements are as near to facts as you will get. Therefore your question is not realistic.