Eventually the roads will erode, releasing the plastics as microplastics. Just kicking the can down the road (so to speak).
Alternatives for plastics don't look good, but a few look better.
1. Used plastic -> recycle to new plastic. Result: $$$ for inferior plastic. Uneconomical so showstopper.
2. Used plastic -> burn as fuel. Result: $ with some nasty air pollutants. Somewhat economical from energy production, but awful health costs, so long term uneconomical.
3. Used plastic -> bury in landfill. Result: $ and sequesters carbon, but will eventually leak into water. Very economical, but high costs in long-term. Drinkable water will be/is the new oil.
4. Used plastic -> pyrolisis into diesel. Result: $$ and can replace new fossil fuel. Can burn cleaner than diesel from crude. Not as economical as diesel from crude, so might need government support to become economically competitive with crude based fuels.
My vote is for #4, pyrolisis into diesel.
https://ir.canterbury.ac.nz/bi...
"The energy consumption for .. pyrolysis .. 1.328 MJ/kg. The calorific value of the hydrocarbon products is about 42.3 MJ/kg... the plastic pyrolysis is an energy-efficient process... This technology can be applied to significantly reduce the conventional landfill or incineration of waste plastics. "