In general, I'd like to see curves on highways realigned so they have a constant radius. Rounding a curve, you can't set-it-and-forget-it as you can in North America. Instead, you judge the curve, set your speed and your steering wheel, get halfway around and - whoops, the radius suddenly tightens, better hope you weren't too close to the limits of traction.
But for a more general improvement I'd like to see roadbeds and surfaces redone for quieter travel and better economy. There were some newspaper articles a few years back about how, because of the particular substrates and surfaces used, our roads were relatively cheap to lay, but required much more maintenance than those overseas, and they sagged so badly under the weight of heavy trucks that the trucks were in effect always driving uphill at a 15% fuel penalty.