A STUDENT PLT BECAME DISORIENTED AT NIGHT WHILE TAXIING AT LGB; IN LIGHT RAIN SHOWERS. THE INSTRUCTOR PLT INTERVENED. THE INSTRUCTOR PLT ALLEGES THAT THE YELLOW CTRLINE TXWY LIGHTS AT LGB TXWY D3 AND RWY 30 SPLIT L AND R IN THE RWY ENVIRONMENT; AND CAN MISLEAD A PLT TO CONTINUE FOLLOWING A YELLOW LINE RATHER THAN CROSS THE RWY TO JOIN THE OTHER TXWY.

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AFTER LNDG RWY 25L; MY STUDENT AND I WERE TAXIING BACK FOR TKOF RWY 25L; FULL LENGTH. ALTHOUGH WE REQUESTED PROGRESSIVE TAXI INSTRUCTIONS; THEY DON'T LIKE TO TAKE THE TIME TO GIVE SMALL ACFT TRUE PROGRESSIVE INSTRUCTIONS RELATED TO THE ACFT'S PROGRESS ALONG THE TXWYS. GND GAVE US A NORMAL TAXI CLRNC DESCRIBING THE RTE BACK ALONG THE S SIDE OF RWY 25L AND RWY 30 AND CLRED US TO 'HOLD SHORT OF RWY 30 AT D3.' SO EVEN THOUGH THE OBJECTIVE WAS TO FAMILIARIZE THE STUDENT WITH THE DIFFICULTIES AND DANGERS OF TAXIING AT NIGHT IN BAD WX AT AN ARPT UNFAMILIAR TO HIM; WE WOULD JUST FOLLOW OUR TAXI INSTRUCTIONS. NO PROB SO FAR. UPON APCHING D3 WE RECEIVED A CLRNC TO CROSS D3 AND TURN L ON TXWY L. THERE'S THE PROB. THERE IS NO YELLOW TXWY LINE TO FOLLOW FROM D3 STRAIGHT ACROSS TO RWY 30! AS MY STUDENT BEGAN TO CROSS D3 HE TRIED TO FOLLOW THE YELLOW LINE; ASSUMING IT WOULD SOMEHOW TAKE HIM ACROSS TO TXWY L. THIS WOULD HAVE PUT HIM IN POS ON RWY 30 AT D3 WITH TFC COMING IN BEHIND. AFTER OBSERVING MY STUDENT'S DISORIENTATION I TOOK THE CTLS AND EXECUTED THE INSTRUCTION TO CROSS D3 TO TXWY L AS I EXPLAINED THE SIT TO MY STUDENT. IT WAS DARK AND DIFFICULT TO SEE ACROSS 30 TO LOCATE THE CTR OF D3 AT TXWY L. A TXWY LINE WOULD HELP A LOT. WE WERE NEVER IN ANY IMMEDIATE DANGER AND DID NOT CONFLICT WITH ANY ACFT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE INSTRUCTOR PLT'S INTENT WAS TO HAVE THE STUDENT CROSS RWY 30 AND TAXI N ON TXWY L TO THE APCH END OF RWY 25L; FOR A FULL LENGTH TKOF. THIS INSTRUCTOR PLT'S CONCERN IS WITH THE YELLOW CTRLINE TXWY MARKINGS AT THIS TXWY AND RWY INTXN. THEY APPEAR TO BE DESIGNED FOR ACFT DEPARTING THE RWY ENVIRONMENT; INSTEAD OF ACFT TAXIING ONTO THE RWY. BY FOLLOWING THE YELLOW LINE; STUDENTS MAY TAXI ONTO THE RWY AND TURN EITHER L OR R; INSTEAD OF TAXIING STRAIGHT ACROSS THE RWY. (THE TXWY LINE SPLITS ON THE RWY; IN EITHER DIRECTION.) ON THE EVENING THAT THIS RPT WAS SUBMITTED; THE FORWARD VISION FROM THE COCKPIT WAS OBSCURED BY RAIN ON THE WINDSHIELD; AND MINIMAL LIGHTING. IT WAS DIFFICULT TO SEE THE BLUE LIGHTS ACROSS THE RWY AND MAINTAIN ORIENTATION DUE TO THE REDUCED VISIBILITY AND THE LOW HT OF THIS ACFT. THIS RPTR AND STUDENT WERE UTILIZING AN ARPT DIAGRAM.