It's not so much that roads are necessary, but that every single lot must be directly adjacent to one - it's entirely reasonable in real life to have large complexes that are pedestrian primarily, connected via some kind of mass transit, where road density is greatly reduced.
This is impossible in SC4, since every single building must be directly adjacent to a road.
Also, because of the city size limit increases between SC3000 and SC4, the pathfinding algorithm used for transit calculations is really barebones - your sims will only ever travel towards their destination. Even there was a direct subway line to their destination right behind them, they won't take it. This makes transit in the game a complete pain, since the model the game follows is counter-intuitive to the max.
The trick of course is, with a grid road network, this pathfinding works really well. This only compounds the problem - since a subway system, no matter how well designed, has a hell of a time competing with a road network - and in no time at all you have citizens screaming about congested roads, and a perfectly good subway system that's sitting at 5% capacity.
There are ways to "trick" the game - mostly involving designing your road networks in such a way that you create disconnected islands between demand zones. In essence, you're creating a ludicrously broken road network nobody will ever use just to get people onto mass transit. But it's worth it (in the game, and IMHO maybe real life also) - the capacity and density of rail mass transit blows the crap out of driving, and allows you to get people much further, much more quickly. Air pollution becomes a complete non-problem
This is impossible in SC4, since every single building must be directly adjacent to a road.
Also, because of the city size limit increases between SC3000 and SC4, the pathfinding algorithm used for transit calculations is really barebones - your sims will only ever travel towards their destination. Even there was a direct subway line to their destination right behind them, they won't take it. This makes transit in the game a complete pain, since the model the game follows is counter-intuitive to the max.
The trick of course is, with a grid road network, this pathfinding works really well. This only compounds the problem - since a subway system, no matter how well designed, has a hell of a time competing with a road network - and in no time at all you have citizens screaming about congested roads, and a perfectly good subway system that's sitting at 5% capacity.
There are ways to "trick" the game - mostly involving designing your road networks in such a way that you create disconnected islands between demand zones. In essence, you're creating a ludicrously broken road network nobody will ever use just to get people onto mass transit. But it's worth it (in the game, and IMHO maybe real life also) - the capacity and density of rail mass transit blows the crap out of driving, and allows you to get people much further, much more quickly. Air pollution becomes a complete non-problem