Exhaust related
 

I have noticed some black ash (like carbon powder) at the end of the
tail pipe of my 1996 civic (212K km). I was able to clean the black
formation using a tissue paper. The muffler is relatively new and the
vehicle is very well maintained (I bought it used). Oil changed in Jan
and May.

I drive the car to go to school which is about 6km from my home. A
friend told me that running the car for such a short distance on a
regular basis would develop problem with exhaust system and will be
difficult to pass the emission test (due Jan 2007).

Any suggestions on what should I do to take care of this problem? I
have decided to run the car on highways for about 15 minutes every
week. Will that be a good thing to do? Thanks in advance.

Other relevant information:
The smoke is colorless and I used fuel injector cleaner a month ago.