There's a lot to engineering a successful heated slab outside. Proper insulation and moisture control (wet soil decreases the efficency significantly), proper flow (you may need a manifold system rather than just a single serpentine run). Then, there is what class system you want: 1, 2, or 3. If I remember correctly, class 1 means snow can accumulate, but it will melt eventually; 2, melting occurs regardless of snow load, but some might accumulate; or 3, hot enough to keep snow off, regardless of the rate (often used around hospitals, etc). To do it right, with minimal operating costs, it has to be sized and installed properly. Depending on the size of the tubing, that spacing might be excessive or too far apart. Adding moisture sensors, temperature sensors, mixing valves can all make it more efficient. There is no need to heat the slab on a very dry day, no condensation to freeze, etc. I've never installed one, but I looking into doing it once for my condo complex (we have a significant hill). Couldn't talk them into it.
Also, you may need a heated drain to dispose of the moisture - you don't want the liabilty of meltwater running into the street and freezing - very bad idea. As is it creating an ice dam at the side of the driveway. It can make the walk to the sidewalk very challenging. Get help from someone who specializes in this is my unprofessional opinion. You can glean some good info from the web, as that is where I got most of mine - don't remember the manufacturers sites I tapped, but google will come to the rescue. Most of the companies that do in-home radiant heating have sections that deal in snow removal - check them out.