I have a small vibe I can plug into the lighter outlet of the car. The vibrator part fits into my panties or thong, with a short and very light cord which is later connected to the car-lighter cord. I put the controller of the vibe on the steering wheel and once I'm on the freeway I just give myself very brief buzzes, a couple of seconds at a time, until I get close (to orgasm). Then I stop, wait about the same length of time it took me to 'get close' before I let myself resume buzzing. Then I buzz again. The times between 'sessions' decreases each time I stop. When the time between buzzes gets down to about 10 seconds or so, I move the little vibe up and down against my clit while I buzz. I can draw this out for a while-the longer the better-but I always cum within 30 to 45 minutes. Sometimes I get too close to cumming before I stop, and I cum accidentally. On long trips I can get at least two or three cums out of this technique. This is a really, really great technique!!!
Warning-do not do this without placing a pad or towel underneath your bottom. You'll get *very* wet! I lower my slacks or hike up my skirt and use a thick towel beneath me.