Will new transportation technologies increase urban density?

Will 21st century transportation innovations work against urban density, as the car did in the 20th century, or promote urban centralization, as the railroad did in the 19th century? Reducing the cost of commuting always reduces urban centralization in the classic Alonso-Muth-Mills model but that result reverses if the number of trips is endogenous and the elasticity of trips with respect to their costs is greater than one. That elasticity may have increased over time, as an increasing share of ...