Speed externalities – the impacts that a driver’s speed choice imposes on others – are usually quoted to justify highway speed regulation in the form of maximum speed limits. However, speed externalities could already be internalized if a pre-existing policy were in place that is related to speed, questioning the traditional rationale supporting speed limits. Given the relationship between speed and fuel consumption and the omnipresence of fuel taxes around the world, it comes as a surprise that pre-existing taxes on motor fuel are completely missing in the debate on the general appropriateness of speed regulation. In this paper we develop an economic equilibrium model of highway speed choice accounting for (i) a market failure – speeding externalities capturing the fact that drivers do not internalize the adverse consequences of speeding on other highway users and the society as a whole; (ii) a famous speed related behavioral anomaly – causing adverse effects drivers impose on themselves by falsely predicting the time saving potential of speed; (iii) a pre-existing fuel tax – closing the wedge between the privately and socially optimal speed. The latter creates a ‘government feedback effect’ reflecting the positive feedback effect of speed on fuel tax revenue and so the broader beneficial fiscal impacts of speed choice ignored by drivers. Numerical computations for Germany indicate a dominant ‘government feedback effect’ ((iii) outweighs (i)) for mean speeds up to around 120 km/h presuming fully variable travel time budgets and beyond that speed level when drivers put (some of the) travel time savings from speeding into more highway traveling. This implies that speed externalities are largely internalized and that the externality rationale in favor of speed regulation does not apply to the majority of drivers. Nevertheless, a moderate speed limit on German highways of 130 km/h would probably not compromise economic efficiency, at least as long as the share of diesel cars is significant. Generally, when drivers are subject to lack of rationality leading to excess speeding, (iii) is not able to outweigh (i). Then, speed limits remain highly warranted provided that appropriate “nudging” is not available. The numerical finding is likely to hold for a large number of European countries too but probably not for North American countries where fuel taxes are considerably lower.

速度外部性（驾驶员的速度选择对其他人的影响）通常被引用为最大速度限制形式的高速公路速度调节的依据。但是，如果已经建立了与速度有关的现有政策，那么速度外部性可能已经被内部化，从而质疑支持速度限制的传统理由。考虑到速度与燃油消耗之间的关系以及全世界燃油税的无处不在，令人惊讶的是，在关于速度调节的一般适用性的辩论中，完全不存在预先存在的汽车燃油税。在本文中，我们开发了一种高速公路速度选择的经济均衡模型，该模型可解决以下问题：（i）市场失灵–超速外部性反映了驾驶员并未将超速对其他高速公路使用者和整个社会的不利影响内部化的事实；（ii）著名的与速度有关的行为异常-通过错误地预测速度的省时潜力而引起驾驶员施加的不利影响；（iii）预先征收的燃油税–缩小了私人和社会最优速度之间的差距。后者产生了“政府反馈效应”，反映了速度对燃油税收入的积极反馈效应，因此驾驶员选择忽略了速度选择的更广泛的有益财政影响。德国的数值计算表明，在平均速度高达120 km / h的情况下，假设完全可变的旅行时间预算，且驾驶员放下时速超出该水平（其中一些），则“政府反馈效应”占主导地位（（iii）胜过（i））。通过加快公路行驶速度来节省旅行时间。这意味着速度的外部性在很大程度上已被内部化，并且支持速度调节的外部性原理不适用于大多数驾驶员。然而，至少在德国汽车中占有相当大比例的情况下，以130 km / h的速度对德国高速公路实施适度的限速可能不会损害经济效率。通常，当驾驶员缺乏理性导致超速行驶时，（iii）不能超过（i）。然后，如果没有适当的“微调”功能，则仍然极力保证速度限制。这一数字发现也可能适用于许多欧洲国家，但可能不适用于燃油税低得多的北美国家。