Scary for sure. I don't own a 4x4 so we always launch with a 2wd. Our ramps get super slick as well to the point where you have to hold on the to the vehicle and take baby 6" steps to get to the trailer to unlatch the bow eye but I have never had an issue with the vehicle slipping. Even on ramps this slick I have never even spun a tire pulling out, empty or loaded. I wonder if the texture of concrete or maybe the type of algae is the difference maker?