PLT OF C208 CARGO ACFT AT ONT BLOCKING VEHICLES AND A COMPANY IN BACK; TAXIED ONTO TXWY S WITHOUT CLRNC WHEN UNABLE TO COMMUNICATE WITH GND DUE TO A CONGESTED FREQ.

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I STARTED TAXIING FROM THE ACR X PARKING RAMP AREA TO UP TO THE ACTIVE TXWY S; WHICH I STOPPED SHORT OF. AS I SAT THERE WAITING TO GET TAXI CLRNC FROM GND CTL; I NOTICED 2 VEHICLES WITH THEIR LIGHTS FLASHING. THE 2 VEHICLES WERE DIRECTLY OFF MY L WINGTIP; ABOUT 10 FT AWAY; AND BEHIND ME WAS COMPANY ACFT. IT WAS CLR TO ME THAT MY ACFT WAS BLOCKING THE ROAD. IT SEEMED TO ME THAT THE VEHICLES WERE IN A HURRY; MAYBE TO DEAL WITH SOME SORT OF EMER. THE 2 VEHICLES COULD NOT GET BEHIND ME NOR COMPANY ACFT NOR THE ACR RAMP -- BECAUSE IT WAS CONGESTED WITH RAMP PERSONNEL AND TUG VEHICLES. GND CTL WAS VERY BUSY; I BELIEVE THAT ONLY ONE PERSON WAS WORKING GND AND CLRNC. I TOLD GND MY INTENTION TO TAXI; HOWEVER THE CTLR WAS TOO BUSY AND I NEVER GOT A REPLY. I HAD NO CHOICE SO I LOOKED AROUND -- NO ONE WAS AHEAD OF ME. I PROCEEDED WITH CAUTION AND TAXIED. ONTO THE TXWY S IN ORDER TO GIVE WAY TO THE EMER VEHICLES; THE 2 VEHICLES THEN PASSED BEHIND ME QUICKLY. ABOUT 2 MINS WENT BY BEFORE THERE WAS A PAUSE ON GND FREQ; WHICH THEN I ASKED GND IF I COULD START MY TAXI. GND CTL REPLIED 'YOU'RE ON AN ACTIVE TXWY...GO AHEAD AND TAXI TO RWY 26L AND CALL THE TWR WHEN YOU GET TO YOUR DEST;' WHICH I DID.