ACR HAS TCASII RA AND TA. LEVELS OFF TO AVOID.

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WHILE CLBING THROUGH 8000 FT TO ASSIGNED ALT OF 14000 FT; PIT DEP CALLED VFR TFC 12 O'CLOCK; CLOSE RANGE AND 9500 FT. SKY WAS HAZY AND HE WAS NOT ON OUR TCASII. WE REDUCED OUR RATE OF CLB AND THE TARGET APPEARED AT 12 O'CLOCK AND 2 1/2 MI ON TCASII. WE LEVELED OFF AT 9000 FT AND RECEIVED A DSND RA. I SAW HIM PASS OFF OUR L WING SLIGHTLY ABOVE AND ABOUT 3/4 MI. WE WERE THEN HANDED OFF TO CLE CTR. CLE INFORMED US THAT HE HAD PASSED THE VFR TA TO PIT DEP. IN THE ATC SYS TODAY THE MOST DANGEROUS AIRSPACE THAT I CAN IMAGINE IS THAT JUST OUTSIDE AND ABOVE A TCA. ALL VFR TFC WITH VFR RATED PLTS AND THOSE NOT WISHING TO PARTICIPATE IN RADAR SEPARATION ARE SANDWICHED BTWN 8000 AND 12500. THOSE NOT EQUIPPED WITH MODE C TRANSPONDERS ARE PACKED BTWN 10000 AND 12500. 10000 FT IS WHERE THE FAA ALLOWS RELAXED CABIN ATMOSPHERE; NONSTERILE COCKPIT AND EXTERIOR LIGHTS OFF. ADDITIONALLY THIS IS AN AREA WHERE AIRSPACE RESPONSIBILITY CHANGES HANDS FROM DEP/ARR TO CTR. NUMEROUS HDOFS AND MUCH COORD IS REQUIRED. I HAVE LONG FELT THIS TO BE ONE OF THOSE FOCAL POINTS OF WEAKNESS WHICH IS A MASSIVE ACCIDENT WAITING TO HAPPEN.