This can be done, but it will take decades and major construction activity. Which may be constrained by the fact that steel and concrete production is CO2-heavy too. (And not just that, AFAIK the Netherlands put very strict limits on construction activity because of nitrogen emissions from the construction vehicles.)
In the West, a lot of the middle class settlements have spread thin and wide, making public transport inefficient. Redensification is possible, but complicated - it involves a lot of people moving and at least some of them losing their gardens.
Meanwhile, construction of new railways or upgrades of existing tracks (including light rail) meets heavy NIMBY opposition on every step, even in countries where rail is widely used for commute (such as in Czechia).
In contemporary developed civilization, it is much easier to ban than to build.
In the West, a lot of the middle class settlements have spread thin and wide, making public transport inefficient. Redensification is possible, but complicated - it involves a lot of people moving and at least some of them losing their gardens.
Meanwhile, construction of new railways or upgrades of existing tracks (including light rail) meets heavy NIMBY opposition on every step, even in countries where rail is widely used for commute (such as in Czechia).
In contemporary developed civilization, it is much easier to ban than to build.