Public Authorities are responsible for setting speed limits on roads. It is obvious that the modification of speed limits affect travel time. Also, there are many academic studies highlighting the relationship between vehicle speed and other particular isolated social costs, such as speed and accidents, speed and pollution or speed and fuel consumption. However, there are very few comprehensive studies on the subject of optimum speed limits. Furthermore, when Public Authorities modify speed limits usually they justify the measure to achieve a particular goal. The aim of this paper is to develop a comprehensive methodology that relies on cost-benefit analyses to determine the optimum speed limit for a particular road. The methodology is then applied to two recent case studies in Spain. In the first one, the Authorities decreased speed limits on national highways from 120 to 110 km per hour to save fuel. In the second case, the Authorities also reduced speed limits on the M − 30 ring road from 90 to 70 km per hour on specific days to reduce pollution. It seems that the Authorities might not always perform a technical analysis of these measures before implementing these policies.

公共当局负责设置道路限速。很明显，限速的修改会影响旅行时间。此外，还有许多学术研究强调了车速与其他特定的孤立社会成本之间的关系，例如速度与事故、速度与污染或速度与燃料消耗。然而，关于最佳速度限制的综合研究很少。此外，当公共当局修改速度限制时，他们通常会证明该措施是为了实现特定目标。本文的目的是开发一种综合方法，该方法依赖于成本效益分析来确定特定道路的最佳速度限制。然后将该方法应用于西班牙最近的两个案例研究。在第一个中，当局将国家高速公路的限速从每小时 120 公里降低到 110 公里，以节省燃料。在第二种情况下，当局还在特定日期将 M-30 环路的限速从每小时 90 公里降低到 70 公里，以减少污染。在实施这些政策之前，当局似乎并不总是对这些措施进行技术分析。