We present a novel methodology for calculating the density of charging infrastructure required to enable electrification of all passenger cars in a large geographic region. We combine this method with models of charging infrastructure cost, forecasts of levelized costs for operating combustion engine and battery electric cars and forecasts of market penetration, to calculate the socio-economic value of passenger car electrification over the 2020-2040 period. Recommendations for urban regions are derived based on application of the method to Stockholm County, Sweden. Electrification is shown to generate long-term savings of up to 1800 euro per car-year and the opportunity cost of delaying the transition by a single year is comparable to the full cost of deploying the infrastructure that enables the shift. Large-scale deployment of dynamic charging is a cost-viable alternative to static charging for full electrification of urban passenger car fleets.