As an avid herpetologist, I want to thank you for not harming that turtle. A lot of those are ruthlessly killed for being "mean", as if they have a choice!
In spite of your well-intentioned repositioning of the turtle, it will probably waddle across the road again, as this is egg-laying season, and the female turtles will exit the water and travel long distances to lay their eggs in holes they dig themselves. They are hard-headed and will continuously try to head the way they want, understandably ignornant of vehicle traffic. Egg-laying is the only time these turtles will exit the water for prolonged periods of time.
And in spite of what someone said here, common snapping turtles do NOT live hundreds of years. The average life span is around 30 years or so. It is the allligator snapping turtle of the deep south that can live in upwards of 150 years. The alligator snapping turtle is an altogether different species and has a much smaller natural range. Also, in spite of their mean looks, they are more docile than the common snapping turtle.
Joe