We present a comprehensive study on the impacts and associated changes in costs resulting from the implementation of Environmental Speed Limits (ESLs), as a measure to reduce PM and associated health effects. We present detailed modelled emissions (i.e., CO, NO, PM and PM), concentration levels (i.e., PM and PM) and population exposure to PM and PM under three scenarios of ESL implementation for the Metropolitan Area of Oslo. We find that whilst emissions of NO and CO do not seem to show significant changes with ESL implementation, PM emissions are reduced by 6-12% and annual concentration levels are reduced up to 8%, with a subsequent reduction in population exposure. The modelled data is used to carry out a detailed analysis to quantify the changes in private and social costs for the roads in Oslo where ESL are implemented today. This involves assessments related to human health, climate, fuel consumption, time losses and the incidence of traffic accidents. For a scenario using actual speed data from ESL implementation, our study shows a net benefit associated with the implementation of ESLs, whilst for a theoretical scenario with strict speed limit compliance we find a net increase in costs. This is largely due to variation in costs due to time losses between the scenarios, although uncertainties are high.