I'm gonna try to clear things up a bit better for those who don't understand how Time Stop in Jojo's Bizarre Adventure works.
It's correct that Jotaro can move in frozen time. And by that logic, DIO can also move in frozen time for 2 seconds. (quoted from previous answers)
This is indeed true to some degree. In a technicality, Dio should be able to move like Jotaro can, but this is not the case. Time Stop can allow for multiple stand users to stop time at the same time or at different intervals if they can move in stopped time.
Jotaro can stop time for 5 seconds and he uses it (refer to time stop) in the 9th second of DIO's time stop, and at this moment, Za Warudo's time stop has been replaced by Star Platinum's and DIO can only move for 2 seconds. He ended up being frozen in the 11th second after Za Warudo was activated, but since it has already been replaced by Star Platinum's (refer to time stop), DIO has used up the 2-second that he can move in frozen time. (quoted from previous answers)
There is, however, a theory that Time Stop can overlap if 2 stands use it, thus leading to the effect of Dio being able to seemingly keep moving after his previous limit was achieved. As stated in the Anime, his peak limit of time stop duration was 11 seconds. Seeing as how Jotaro supposedly stopped time for 5 seconds and stopped it at the 9th second of Dio's Time Stop while moving in stopped time, this evidence can support this theory as the visual and audio effects of Time Stop going into effect is only seen when time is flowing like normal.
As for the road roller, I can kinda see why Dio would want to make sure Jotaro is dead by crushing him with the heaviest thing he could find. Like he said, "You can never be too careful when handling with the Joestars." Where he found the road roller is what stumps me.
stops timethen only they can move on the stopped time