I always thought expressways are an important thing missing from the late game. In modern world, many large cities have far-spanning suburbs thanks to expressways. Here's my thught's on it:

1- Build Expressway would be worker action requiring Industrialism and combustion.

2- They are as roads for movement purposes (because tanks and other military equipment can already travel at their max speed in normal roads)

3- If a tile with cottage/hamlet/village is connected to a city with expressways, its growth rate is doubled.

4- If a tile immediately outside the city radius (within the 2nd culture level radius for city of culture level 1; within the 3rd level culture radius for cities with fully developped workable areas) is connected to the city through at most two other expressway tiles, that tile becomes included in the city's workable tiles.

5- To gain any of the bonuses, the city must have access to oil.

I never modded in civ4, and I certainly can't mod to the complexity above. I thought I might throw this idea in here and see if anyone is interested.

That's a great idea, if I can find time I might have a go at that :) .

That's a pretty excellent idea, and doesn't seem very complex.

One thought---what's the behavior if that civ is running the Emancipation civic? (4x growth?) What about Police State? (only 1.5x growth?)

One thought---what's the behavior if that civ is running the Emancipation civic? (4x growth?) What about Police State? (only 1.5x growth?)

I suppose so, given the speed growing metropolises spawn suburbs in our time.

or maybe it will be more balanced to word it as +100% growth rate, instead of double. That way, with emancipation it will be 3x. But doesn't really matter, the main bonus it provides is the extra workable tiles in the 3rd culture radius in my opinion.