Most people say it is a bug of DYOM scripts and propose you to remove traffic and try to set the route points so that they don't hit objects (i..e street poles.)
My own theory is the coordinates you set the route point: x; y; z. I say that because we are given a Jet Pack to go from a route point to another one faster. Let's say your first route point (which works perfectly) is at coordinates: 55; 17; 33. Let's say your second route point, which is five meters away from the next one: 60; 17.51; 33. The second Y (17.51) could be what makes the driver make circles: mostly due to setting the route point while not completely on the ground level.
Another reason could be that the route point is too far, meaning it would be some more leading to it. Or also: driving too fast in a corner can provoke such a reaction.
To conclude: it's mostly luck (sometimes it will not do it, even after ten tries; other times, it could do it twenty times in a row.)