Harnessing the Deaths of Unfortunate Animals
While it is advisable to not use the remains of animals killed by vehicles in necromantic practices there is another thing that can be done with these former lifeforms. One can set up a dedicated altar in the vicinity and take small tokens from these unfortunate creatures. By placing a few hairs or something similar in a bowl on the altar from each piece of roadkill you create a magical connection to the site of their death.
This can effectively allow the lifeforce released from the animals death to be channeled to the altar and through that down into the ground below. In this manner you can both honor the creature's death and ensure that their sacrifice is not wasted by rerouting the released lifeforce to vegetation surrounding the altar. Furthermore if you place small offerings of the kinds of food consumed by the slain creatures when they were alive you can ensure that their spirits rest easily. This is recommended because restless animal spirits can lure others of their own kind to their doom at the site of former deaths.