You’re not allowed to collect roadkill that you have killed (presumably to stop people actually trying to kill stuff).
But the car behind can pick up,reminds me of my mate ,phone call one morning ,Ive got a Deer ,can you butcher it for me ,had to pick it up ,else next vehicle would be quarry lorry n would be mashed into road.(butcher by trade).
Rule of thumb if its still warm it’s fresh .