B737-300 CREW EXITING ON TXWY T; AND A BRASILIA TAXIING W ON TXWY B; ALMOST COLLIDED.

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AFTER LNDG ON RWY 28R IN SAN FRANCISCO AND TURNING OFF ON TXWY T; WE WERE CLRED TO CROSS RWY 28L. I ELECTED TO CONTINUE ON TXWY T; EXPECTING TO TURN ON TXWY B TO CONTINUE TO OUR GATE. AS WE CROSSED RWY 28L; I OBSERVED A BRASILIA MOVING W ON TXWY B AT AN ABNORMALLY HIGH RATE OF SPD. I HAD TO APPLY BRAKES TO AVOID A COLLISION. THE BRASILIA AIRPLANE NEVER SLOWED. UPON CONTACTING THE TWR LATER; A PERSON IDENTING HIMSELF AS A SUPVR INFORMED ME THAT THERE IS SUFFICIENT ROOM TO STOP THE AIRPLANE ON TXWY T WHILE HOLDING SHORT OF TXWY B. IF ONE WERE TO DO THIS; THE AIRPLANE WOULD BE ON THE RWY SIDE OF THE HOLD SHORT MARKINGS. DON'T AIRPLANES EXITING ACTIVE RWYS HAVE RIGHT-OF-WAY OVER AIRPLANES TAXIING ON ADJOINING RWYS? AREN'T WE SUPPOSED TO CLR ACTIVE RWYS EXPEDITIOUSLY? MANY RWYS HAVE SHORT PARALLEL OR ANGLED TXWYS FOR EXITING THE RWY WHICH REQUIRE INTRUSION ONTO PARALLEL TXWYS IN ORDER TO CLR THE ACTIVE RWY. THE TWR SUPVR ALSO INDICATED THAT TXWY T IS A SPECIAL TXWY; AND THAT THE AIRPLANE IS IN FACT OFF THE ACTIVE RWY IF ONE STOPS SHORT OF TXWY B. IF THAT IS THE CASE; WHY ARE THE HOLD SHORT LINES PAINTED WHERE THEY ARE ON THE TXWY SURFACE? HOW CAN ONE BE ON THE RWY SIDE OF THE HOLD SHORT LINES AND STILL BE EFFECTIVELY CLR OF THE ACTIVE RWY?