Properties of Aluminum and Carbon Frames?

[Veronica]

Would I need more of a touring bike instead of a lightweight racing style for highways?

No, not really. My steel bike that I use for touring and unsupported rides is actually a cross bike. I use that bike when I want/need to carry more stuff. Mostly because I think my Cervelo would look ridiculous with a big bag on it.

Veronica

[pll]

I wonder if the vibration you felt was what people refer to as "speed wobble" or "shimmy". Some references to it:

• On Sheldon Brown's web site
• Wikipedia
  
• Bike Radar
• Discussion in Cycling Tips (with a video)

I would have your LBS rule out any equipment problem, but it appears that the wobble can happen on any bike. Luckily, I have never felt it. From the articles, some things that appear to help: unweighting the saddle, perhaps by standing on the pedals, pressing a knee against the top tube, keep the cranks horizontal and not vertical if you are coasting down, not having a 'death grip' on the handlebar.