But that was over a hundred years ago. Ruddy's engine design has evolved considerably, so that in order to use alternate fuels, the engine or the fuel have to be reworked.
While it can be done, the transformation would be slow and expensive, in order to not bring commerce to a standstill.
Used vegetable oil wouldn't even be a pisshole in a snowbank compared to demand, so I would suggest that to be collected and used by dedicated engines. Perhaps stationary diesels used by municipal power plants, schools, or sewer authorities.
For commercial transportation (read trucks), new vegetable oil would have to be brought online at a rate. making the engines to use it efficiently a realistic choice for the truck buyers. A very large juggling act that only the feds could manage, I'm afraid. Of course whenever the feds get involved, smart choices and logical solutions, seem to go down the drain.
