TFC CONFLICT 20 MI E OF BWI AT 10000 FT RESOLVED BY FOLLOWING A TCASII RA.

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RTE OF FLT CLRNC WAS DQO V166 BELAY DIRECT DCA DIRECT LDN J134 COLNS.... FO WAS FLYING ON AUTOPLT AT 10000 FT MSL. JUST PAST BELAY INTXN; WE GOT A TA ON TCASII. TFC WAS HEAD-ON SHOWING 200 FT BELOW. ABOUT 15 SECONDS LATER WE GOT AN RA FOR US TO CLB. WE FAILED TO GET THE TFC IN SIGHT. WE CLBED TO 10600 FT WHEN THE FO SPOTTED THE TFC GOING BY TO OUR R ABOUT 1 NM HDG E. WE WERE FLYING A 'LOW ALT ESCAPE RTE.' THIS WAS SOMETHING NEW TO MYSELF AND THE FO. I DON'T KNOW IF THIS IS COMPANY GENERATED OR SOMETHING WITH ATC TO HELP RELIEVE CONGESTION IN THE PHL/DCA AREA. THIS ROUTING KEEPS US AT 10000 FT UNTIL WELL PASSED DCA BEFORE WE CLB. I CALLED PHL APCH TO WARN THEM OF OUR RA; BUT THEIR ANSWER WAS THAT WE SHOULD BE TALKING TO BWI. APPARENTLY; PHL FORGOT TO SWITCH US. I THINK THAT WITH US AT A LOW ALT WITHOUT POSITIVE CTL IS HAZARDOUS. PHL DEP WAS VERY BUSY DURING THIS TIME. THE FO AND I DISCUSSED THE POSSIBILITY THAT WE MISSED THE CALL BUT IT WAS DOUBTFUL. IN ANY EVENT; A DEDICATED FREQUENCY TO CTL JUST THESE FLTS WOULD CUT DOWN ON FREQ CONGESTION. I SHUDDER TO THINK WHAT MIGHT HAVE HAPPENED IF OUR TCASII WAS MEL'ED THAT DAY.