What you're asking for is what I usually see referred to as the
Appian Way. I have this Wonder laid out, but there's an XML tag missing. Here's what I have for the moment:
- Requires Construction
- Obsolete at Railroad
- Requires Paved Roads building (3 total)
- Cost 500 hammers, double production speed with Stone
- +2 culture, +2 GPP (Great Merchant)
- +50% trade route income
- +1 Road and Paved Road movement
The last part (+1 road movement) is an XML tag that's missing. You can adjust a route's movement with technologies or events, but not with buildings. I'd like to be able to adjust Road/Paved Road movement with the Appian Way and Railroad/Electric Railroad movement with the Golden Spike.