That seems rather efficient in terms of space. Making race tracks of any kind multi use is tricky. At least with full size tracks (think 5km road length or so) park area can definitely be made in and around, but cart tracks are pretty compact. In that image I don't see anything that can be cut out while maintaining safety and functionality. Some races also use temporary road circuits but that brings in other issues from the massive effort required to set up and take down for just one event per year.

I think the primary pollutants from car racing in general are exhaust and micro-plastics (rubber from the tyres wears off on the road and gets into the environment). Both can certainly be mitigated.

Even so, I wonder to what extent we'll allow polluting activity on a small scale for hobbies and entertainment. Of course polluting just for fun isn't necessary (fireworks for example) but amateur/hobby sports definitely have a place in a socialist society.

They could also develop electric go-karts as well. They don't need to be powered by fossil fuels. My local go-kart place is just inside a big warehouse and they just move tires around to make differently shaped tracks, that could certainly be an option for it rather than building a whole dedicated racetrack.

If we banned cars and introduced free public transport, go-karters could have the roads practically to themselves without needing bespoke racing tracks that only have one use. There might be pedestrians and cyclists but the cyclists are used to it because of cars and pedestrians are slow, so easily avoided.