Not necessarily. One of the problems with high density is how to handle peak loads, like for rush hour. There's a limit to how many people can be on a metro, g

Not necessarily. One of the problems with high density is how to handle peak loads, like for rush hour. There's a limit to how many people can be on a metro, grocery store, etc. There's also a hard limit on how much you can scale the infrastructure before residents start choosing transportation options, that make the issue worse (like cars). The infrastructure also have to support a significant increase in garbage creation and resupplies for stores. If one of the main traffic arteries are blocked, the spillover to alternative routes might exceed the capacity and create delays, which are incredibly expensive. A lower density neighborhood, might not use the infrastructure as close to its maximum capacity on a day to day basis, but that creates redundancy for when a road is closed for maintenance and significantly lowers the risk of expensive delays. As with everything, there's several trade-offs between the options, and I think it's hard to give a definitive answer on what has the lowest emission, etc in a cradle to grave analysis. My personal preference is to take all such estimates with a significant "milage may vary" disclaimer