“Fill It With Regular” by Michael Shea (1986)
A gasoline additive spawns a fungus that hungers for oil-based materials.1 I love the way Shea works his rhetorical muscles here:
…. He drove fast, as the few other cars on Redwood were doing, slewing and screeching. His tires were spongy now, taunting him with collapse. He rolled past vineyard and pasture, trailer parks and sprawled junkyarded country houses. Fine fungal lawns toupeed all asphalt-shingled roofs — white lawns where antennas stood like stark, futuristic trees. Furred garden hoses lay in yards like feathered snakes in the grass. The pallid fuzz outlining window frames baffled him till he realized the monomers composing most caulks were hydrocarbons. On one porch he saw a shuddering puffball shape — just discernibly a dog, on its back, fighting to breathe, its paws kneading the air. Ken’s rear left tire gasped, and sagged, and started jouncing. He braked, the brakes locked, the Maverick came ass-around, crossed the shoulder, dropped its rear in a rain ditch, and blew the tire on the right.
Raging, he got out hugging his bag, hotfooted across the sporulating mat, and jumped the ditch. He landed ankle-deep in sweet, sane, earthly grass — and partly in a cowpat. He roared some nouns and gerundives, found and flung an-illogical rock at his car, whose front left tire sank with a wet cough. Ken broke out a beer and strode north, hurrying not to hear the last tire go. He stooped through the wire and straddled the wooden fences, and tiptoed the high- way only where berry-choked streams compelled it. The space he moved through now was that magnified space into which everyone emerges from a failed car — full-scale space, toilsome and time-swallowing, where to reap one aim or object, you had to plow across acres of hours. “I should’ve stocked up better,” Ken muttered. He shifted his burden and cursed the weight of the stew.
Dale was where he had left him, but sitting straighter, rapt in the newscast again. “Enzyme slicks, Kenny! Like a sudden digestive assault. What is it, near nine? Look there!”
"Man! That’s 101 north of Novato?”
“Yup! Just where the southbound backup always starts — and I think its being rush hour’s saved a lot of lives. From there on down, no one was going very fast when the fungus came on.”
They watched an aerial view of confluent freeways where, at this hour, San Francisco-bound traffic routinely braked to join a creeping clog twenty miles long. Today the free-flowing traffic had come up on the clog at lower than usual speeds, though generally drivers had managed to maintain a cautious, coping flow over this invader of their path. They came in slower, but the enzymatic sweat was brutally sudden in its increase, and their tires had turned greasy in their swift liquefaction. Brakes jammed fruitlessly. With seeming abandon — some with fey, balletic half turns — cars skied into the phalanxed bumpers of the idling backup.
Now the clog sat unmoving on twenty miles of flats, smoke penciling up here and there from the rivered vehicular jigsaw. South of the crazed skewing of the pileup zone, the jumbling of the derelict armada was less severe, though everywhere were sideways chromeboats with crumpled corners, ram-welded pairs of tailgating muscle-cars, and jacknifed serais pillowed on luckless imports. Diced safety glass, like a sugar spill, everywhere jeweled the prickly vigor, the pubic wetness of the mold….
The Magazine of Fantasy & Science Fiction, October 1986
[1] A subsequent unrelated novel-length treatment of a genetically engineered thingummy that eats the world's oil-based products: Ill Wind (1995) by Kevin J. Anderson and Doug Beason. It's a hard-sf pseudo-doomsday with a rebirth of Casey Jones as folk hero as a tertiary parenthetical motif. It's a novel worth seeking-out.