Think I'd prefer a motorway at night to a dark field. Not that I've ever done it, but I'd use my remaining height to dive low over the traffic in the direction it's going. Any car's going to come to halt if a plane swoops down in front of them, but you needn't cause them to do an emergency stop and get shunted. Once the traffic under you has stopped, you put your flaps in, kill your airspeed to less than the traffic in front, which you can't fail to miss if they keep moving faster than you are. Aim to land on the hard shoulder - only one lane would need to swerve round you if it came to it and you can pull off onto the verge once your speed is low enough. Motorways tend to be lit from the centre, not the edge, so the most you'd take out is a couple of 100yard markers. And if you're unlucky, maybe an SOS phone...