When a road is under repair, it is often necessary to reverse traffic flows. Special variously shaped dividing blocks are used for this purpose.
Contradictory requirements are set for such blocks. Not to be displaced, they must be heavy. But to be easy to carry and mount, they must be light.

To solve this contradiction, hollow blocks with a plug in the lower part are used. Two workers easily carry such a block and put it in a desired place. Then the block is filled with water and is ready to perform its functions. This solution gives one more advantage – a water-filled plastic block is much safer for drivers than, for instance, a concrete one.
Water will certainly freeze in winter, but who repairs roads at subzero temperature?