Since we are pedantic, what you say isn’t true.
The tanker weights exactly as much as the weight of the water that it displaces. They are in balance. You describe it yourself. The tanker sinks deeper if it becomes heavier and swims more up as it becomes lighter.
The measure of “boat swims” is not the weight of the displaced water. It is wether there is some boat wall left sticking out of the water to keep more water from entering and displacing the air that keeps the submerged volume in weight balance with the water.
We could increase the training requirements and oversight. We could design road-networks in a way that makes speeding more difficult and enact stricter speed limits.
Whenever these measures are taking in an area they greatly reduce the number of people killed or seriously injured.