You need a boat horn. As you pass the driveway were the automobile is preparing to leave you give them a three second burst. You inadvertently timed it so you were never were they were looking for traffic. This is easy to do when they are distracted with there cell phone, coffee and tobacco. I use my very loud voice to say hello. I have had to yell as I approach a side road or driveway and they are starting to roll into the road. For a flashing taillight to work it has to be in there line of sight. The same with a bright or flashing headlight for daytime use. I frankly believe that high viz clothing has very little effect. There wasn't a bike lane. A painted line in the road wouldn't make it safer.