WHILE ATTEMPTING TO GAR AN MD88 HOLDING NEAR THE RWY; A SECOND MD88 CREW MISJUDGED THE EDGE OF THE HARD SURFACE AND DEPARTED THE TXWY.

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ACFT WAS PUSHED OFF GATE XX IN SAT AND THE ENGS WERE STARTED. THE ACFT WAS GIVEN TAXI INSTRUCTIONS TO RWY 3. THERE WAS ANOTHER ACFT HOLDING SHORT OF RWY 3 ON AN ATC HOLD. WE ATTEMPTED TO TAXI AROUND THE ACFT THAT WAS HOLDING SHORT WHEN OUR L MAIN GEAR DEPARTED THE TXWY. IN NIGHT OVCST SKIES; THE DISTANCE BTWN ACFT WAS HARD TO DETERMINE. WE ASKED GND TO HAVE HOLDING ACFT MOVE UP TO PROVIDE MORE ROOM. WE THOUGHT WE HAD ENOUGH ROOM TO PASS BY. THE TXWY EDGE LIGHTS WERE LIT AND I THOUGHT I WAS ON HARD SURFACE. THE TXWY EDGE LIGHTS WERE IN A GRASSY AREA AND THE L MAIN WHEEL ENDED UP IN THE MUD. RECOMMENDATIONS: IF THE TXWY EDGE LIGHTS ARE DISPLACED FROM THE HARD SURFACE TXWY; THERE SHOULD BE MORE DISTINGUISHING MARKINGS EITHER ON TXWY OR ON TAXI CHART OR IN SPECIAL GREEN PAGES TO INDICATE THAT THE TXWY EDGE LIGHTS ARE NOT ON THE WT BEARING SURFACE. IT WOULD ALSO HELP IF THAT AREA HAD BETTER LIGHTING. SUPPLEMENTAL INFO FROM ACN 532650: CAPT WAS NOT CLRING L; FO WAS ACCOMPLISHING CHKLIST AND CLRING TO THE R AT THE OTHER ACFT.