According to road users, the speed limits in Hokkaido, Japan are considered unsuitable. Therefore, this study was undertaken to determine a better speed limit, which would be more efficient, in other words, a sustainable speed limit, by applying user life cycle cost (user LCC). User LCC is composed of cost from travel time, vehicle operating cost ( VOC ), emitted pollution (CO₂, NOx and noise), accidental cost, and congestion cost. The costs from travel time here were inversely proportional to the travelling speed. For VOC and cost from emitted pollution, the highest costs were generated while drivers were travelling at a too high or too low speed. The accidental cost was directly proportional to travelling speed. Lastly, the congestion cost was introduced to make the model more reliable and useful even though it is not a serious problem in Hokkaido. Here, the sustainable speed limit was calculated as the speed that has the lowest user LCC. Costs were calculated in units of yen per kilometre per day. The results showed that urban national highways had the highest costs while the rural national highways had the lowest cost. The sustainable speed limits could be 10 km/h higher than present speed limits on urban national highways, rural national highways and urban expressways, except for rural expressways that was 10 km/h lower. However, due to limitation of data, the results may not contribute towards the sustainability to the environment and city effectively. Moreover, in the future, if traffic volume and other costs change, it is recommended that the sustainable speed limit be reconsidered. JEL Classification: R41, L98, Q51