Why are the roadside land covered with plastic sheets?

very often you always see on the roads of singapore, the land beside the walk way (usually muddy ground) are covered with plastic sheets. any idea why is that so? what function does the plastic sheet serve?Why are the roadside land covered with plastic sheets?
It's like when they use pesticide on strawberry plants. They cover the ground with plastic so the pesticide doesn't go up into the air. That way they can use more toxic pesticides as well as use less of them in terms of quantity since they don't worry about evaporative losses. Some chemical tend to sublimate into the atmosphere and the plastic slows it down.Why are the roadside land covered with plastic sheets?
If they are on a hillside it could be erosion control.
kills the weeds

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