This seems easily fixable, no? Just make cars opaque black and assign progressively decreasing z-index to each spawning light. (Unlikely anyone will leave page open long enough to reach min value, and you could just reset at that point.)
The tricky thing is, this project's renderer is currently a queue of circles to draw to a canvas. It's under 100 lines of JavaScript. So any increase in complexity will require substantial changes, like abstracting over types of drawables.
Anyways, run this in your browser inspector to hot-patch the live demo so that each car has an opaque black circle as its body/chassis:
for (let i = 0; i < cars.length; i++) { console.log(i);
cars[i].headlights = cars[i].headlights.concat([ {xy: new V2d(0,0), z: cars[i].headlights[0].z, r:cars[i].headlights[1].xy.x, col: "black"} ]);
cars[i].rearlights = cars[i].rearlights.concat([ {xy: new V2d(0,0), z: cars[i].rearlights[0].z, r:cars[i].rearlights[1].xy.x, col: "black"} ]);
}To be clear, since of course this is the internet and one must be precise or else get nit-picked and "outplayed," I obviously meant 5 minutes for the author who already knows the layout of the code. Obviously. Any charitable interpretation would have taken that as a given. 25-40 minutes sounds more appropriate for a newcomer examining it for the first time.