From my training, I wouldn't try to resuscitate the patient. Firstly, it is obvious the cardiac arrest was secondary to some sort of other massive injury sustained from the accident, which means that he has almost no chance of living unless you can fix the injury that caused the arrest. If, for some reason, the patient had a cardiac arrest and THEN crashed I would still not resuscitate for very long. The patient is in PEA (which has a very poor survival rate).
I would ascertain from the bystanders what happened (attempting resus while doing so), see the pt was in PEA and then stop resuscitation efforts if there was no ROSC within 10min. After deciding to stop resus then hand over pt to Police on the scene to deal with.