This paper assesses the potential environmental impacts of a large-scale deployment of off-hour deliveries (OHD), focusing on CO2 and pollutant emissions. We use a methodological framework involving four steps: transport demand estimation, traffic simulation, emissions calculation and emissions environmental social cost calculation. Based on five scenarios, depending on the scale of the shift to OHD, and applied to the case of the Lyon urban area, we find that OHDs lead to a reduction in CO2 and pollutant emissions. However, their impact is rather small. The maximum reduction in CO2 emissions is 3.4% for 100% OHD for the whole urban area of Lyon (1.9 million inhabitants and 3325 km2). Some factors (population size, density, traffic conditions, research methodology, vehicle fleet composition, etc.) limit the comparability of the results obtained from other case studies. One of the reasons for this low environmental impact of OHDs is that the LUA is a small and not very congested metropolitan area. This impact is 5% when we focus on the densest area (core of area with 0.7 million inhabitants on 2.2% of surface area) which is more important than in the least dense area (outskirts of area with 0.6 million inhabitants on 83.6% of surface area) with 2.6%. These results confirm the limited impacts of OHDs in smaller, less congested urban areas. It also reaffirms the need for OHDs to be implemented in the densest parts of metropolitan areas. The maximum decrease in the environmental social cost is 4.25 million euros per year. Furthermore, the analysis reveals that the adoption of OHD makes it possible to achieve gains of 2.5 million hours per year in travel time that augur a productivity gain for all the actors involved in urban goods movement.