Ahhh, tickling in a car.
When I was but a budding fetishist, late in high school, I had what could best be described as a "tickle slave" - a hot girl who thoroughly enjoyed being tied up, blindfolded, tickled senseless, then having her brains fucked out. One evening (early morning, really) I met her and handcuffed her wrists behind her back (this was when I thought handcuffs were cool). I put duct tape over her mouth and a blindfold over her eyes, then sat her in the back seat on the passenger side. I buckled her in, took off her shoes (she was wearing black thigh highs and a black one-piece dress, with black heels), and tied her ankles together with a necktie, then poked her bound ankles through the headrest of the front passenger seat. I used the ends of the necktie to bind her ankles to the stems of the headrest then cinched it down on her ankles snugly.
After making sure she was as comfortable as she could be, I drove her into the city from the burbs, where I picked her up. The entire drive was an anticipatory experience for her - blind, unable to speak or move, she could only wait for me to hit the brakes. Every time I stopped at a red light (and only at red lights), I'd reach over and begin tickling her incredibly ticklish stockinged soles. Muffled giggles, squeals and snorts would mosey their way from the back seat. It was about a half hour drive, and it was thoroughly enjoyable.