There are certain rules that should never be broken because it is made for the benefit of the many. Now, some of these rules would keep you safe and others are there to set things in order. Nevertheless, we should always obey them as these rules are made for our good.
Likewise, it is not safe to stand on a moving vehicle, especially the larger ones like the bus and trucks because we might fall while doing that. Now, of course, no one will be foolish enough to do that unless you are a moron. Not only that you will be laugh at, but also you will be endangering yourself.
However, this game makes that possible as your character would be standing at the roof of the truck. The truck keeps moving forward. Your character is a bunny that need to jump to get some object to keep the truck moving. However, there are certain things that you wouldn't want to get as that might slow you down or kill the bunny. You need to remember that you need to feed the bunny too, so get those carrots. You need the fuel to run the truck. This is a race and you need to win it to advance to the next level.