2004 Honda City Car vibration

Hello,
My car usually vibrates almost always, although the engine insulators are not worn that much. I can drive for hours on in-city roads and the car would vibrate all the way (with and without ac). However, when I drive on the freeway for about 10min at 90km/h, the vibrations almost stop and the car feels really smooth for the rest of the ride even after I get back to slow roads.

I would like to know what this speed is temporarily "fixing" such that I'd fix it myself for good.

Thank you.