09 steering feels jittery/shaky

I'd say that your observation is fairly typical and normal...

The Prius has relatively light steering. If your front suspension needs alignment or if your tires are worn then the handling feel will get worse.

Another issue is that some owners may turn the steering wheel more than needed to compensate for road changes, which exacerbates the feeling of not being in control.

 

Hi Gmtran,

You probably need an alignment. The front wheel toe-in tolerance on a Prius allows slightly negative settings. Have them set it positive, buy within spec. The other issue is the rear wheel toe-in which there is not an adjustment provided. So, getting it right requires shims. Somebody on here will tell you what shim thickness to make for your readings.

My car had very sedate steering even at 70 with lots of wind and high speed semis at 15 deg F when I drove it home 384 miles. Although the wind was steady, and the angle to the car was varying depending on the road I was on.

If the problem occurs due to cross-wind gusting, only, then you are going to want to get a chassis brace like the BT Tech plate. My car was all over the lane with 40 mph gusts at 65 mph. Until I put the BT Tech plate on. I did testing where I held the steering wheel perfectly aligned with the car during a gust, and the movement during the gust was large. Due to the time delay and long period of the car's motion in response to a side-gust, its difficult to counter with the steering, and indeed, as Paul has indicated can make things worse. With the BT Tech plate, this all changes, and one can counter steer to keep the car easily on track.