The case for speed limits

This is Simon, a software engineer at Datawrapper. This week I’m looking at data about German motorways and the current speed limit debate.

Germany, home of such legendary car makers as Porsche, Mercedes, and BMW, has one of the most sophisticated motorway networks in the world – the Autobahn. At the same time, Germany is one of very few countries without a general speed limit. Therefore, on at least 18,000 kilometers of German motorways, you are allowed to drive as fast as you can.

The abolition of speed limits on motorways dates back to the Wirtschaftswunder years of the 1950s when the car was a symbol of technological and economic progress. To this day, cars are an important part of Germany's national identity, which includes, evidently, free and unrestricted speeding on the Autobahn. The German aversion to speed limits has been explained as a quasi-religious obsession, similar to the debate around gun control in the U.S.

From a rational point of view, the problems associated with fast driving seem obvious — they include noise, air pollution, and a higher risk of serious accidents. And then, of course, there is the climate impact. As the chart below illustrates, CO2 emissions rise drastically at speeds beyond 80 km/h. For the given example, a modern passenger car meeting the latest European emission standards, CO2 emissions double between 80 and 160 km/h, the latter speed being quite common on unrestricted sections of the Autobahn.

Because of the negative effects of speeding, several attempts have been made to introduce a general speed limit in Germany. But conservative and libertarian politicians have fiercely fought any new regulations, often using misleading or unsubstantiated claims. Andreas Scheuer, mostly remembered for his questionable track record as a former transport minister, famously said that a speed limit was “contrary to every common sense”, therefore completely ignoring a wealth of research by government agencies and other institutions. To counter this irrational notion, I'll try to debunk some of the most popular myths and misrepresentations surrounding Autobahn speed limits.

Myth #1: People don’t actually drive that fast

Opponents of speed limits often claim that the majority of people do not regularly drive faster than 130 km/h, or, in a similar argument, that there are only very few motorway sections without speed restrictions. Based on these claims, they conclude that a general speed limit would simply be unnecessary.

If we look at the data, however, the picture is quite different. In Germany, 18,000 kilometers of motorway have no speed limits, which means that you can legally speed on roughly 70% of the network. Only less than a third of all motorways have some form of a speed limit, either temporary or permanent. Also, an official study of motorway traffic from 2010 to 2014 by the federal road agency BASt shows that speeds beyond 130 km/h on German motorways are indeed normal, even on sections that already have speed limits in place. In a more recent analysis of car navigation data, a team of data journalists from Zeit Online showed that a third of all car traffic on German motorways is faster than 130 km/h. They also found that a large share of drivers routinely ignored existing speed limits.

Myth #2: A general speed limit would slow everyone down

This somewhat contradicts myth #1, but it is still an idea that resonates with many people. However, dense motorway traffic actually flows better at moderate speeds, as smaller differences between fast and slow vehicles reduce friction caused by braking and accelerating in dense traffic. That means, while a speed limit would indeed slow faster drivers down, it may also have positive effects on overall traffic flow.

Related to this argument is that there would be a certain economic loss due to reduced speed. This is mostly based on the idea that time spent in traffic comes with a cost for drivers and that slower driving is therefore more expensive. But a case study in the German state of Brandenburg found that even where speed limits did slow traffic, the costs from time lost with a limit of 130 km/h were more than offset by the economic benefits of preventing traffic accidents.

Myth #3: The climate impact of speed limits is actually tiny

In the current debate, this seems to be the favorite argument of speed limit opponents. And while it is true that the direct effect of a general speed limit of 130 km/h would be relatively small compared to Germany’s overall emissions, it could still save millions of tons of greenhouse gas emissions per year. As outlined in a 2021 report by the German environmental agency UBA, a speed limit could reduce emissions by up to 6.2 million tons of CO2 equivalents, which is 14% of the current emissions from car traffic on German motorways.

Given that Germany has to reduce traffic emissions substantially and that a general speed limit would not have any serious negative impact on people’s lives, the speed limit should be low-hanging fruit for policymakers. Other measures, such as higher gas taxes, road tolls, or driving bans for older vehicles, would have much more serious implications. Also, as this UBA report points out, a general speed limit is expected to have secondary climate benefits down the line. It could make high-performance cars less attractive to consumers, boost sales and production of energy-efficient vehicles, and reduce the use of cars in long-distance travel in favor of high-speed rail.

Myth #4: The climate impact of speeding is obsolete with electric cars

This is my favorite argument on this list because it is so easy to debunk. While it is obviously true that battery-powered electric cars do not have direct greenhouse gas emissions, they are still subject to the same basic physics as any other car. At higher speeds, they produce more noise and particulate matter due to tire abrasion, and they also need substantially more energy due to air resistance. The actual greenhouse gas emissions depend on the energy mix used for charging the batteries, but as long as we do not have abundant climate-neutral energy, it makes sense to save energy by driving at lower speeds.

Myth #5: A general speed limit would not make roads significantly safer

Some opponents argue that Germany’s motorways are “the safest in the world” and that therefore, a speed limit would only have a marginal effect on road safety. This sounds obvious to many Germans, as we are very proud of our world-class cars, roads, and driving education. However, there is no data supporting the claim that German motorways are significantly safer than those in other countries. When looking at fatality rates per kilometer, Germany’s motorways are not even in the top ten of Europe, let alone the world. In fact, German motorway fatality rates are regularly worse than the E.U. average.

Of course, some countries that already have speed limits also report higher fatality rates. That is because many factors contribute to road safety, such as traffic density, road infrastructure, geography, and general driver behavior. A better approach is to compare motorways within Germany. In an analysis of data on motorway accidents in Germany, the data journalism team at Der Spiegel found that there are fewer severe accidents and fatalities when speed restrictions are in place. Based on that analysis, they suggest that introducing even a moderate speed limit of 130 km/h could save up to 140 lives per year.

Much of the opposition to a general speed limit is based on the fact that it will not, in itself, solve the larger problems. A speed limit alone will not prevent all traffic fatalities, nor will it save the climate. However, no single change to the transportation system can do this. A broader transition may include much bigger changes, such as phasing out petrol and diesel cars, prioritizing public transport over individual car ownership, or improving the infrastructure for cyclists and pedestrians. 

In the end, a general speed limit is just a small step on a long way toward a more sustainable transportation system. It is, however, a first step that would be very easy to take.

Data and credits

The data for the graphics in this blog post comes from multiple sources. The choropleth map on top extends on an earlier version made by my colleague Daniela Haake. Other data is taken from the following sources:

• Spiegel Online: Tempolimit könnte bis zu 140 Todesfälle im Jahr verhindern by Patrick Stotz
• Zeit Online: Wo Deutschland rast by Kai Biermann, Paul Blickle, Andreas Loos and Sascha Venohr
• Umweltbundesamt (UBA): Klimaschutz durch Tempolimit 
• Bundesanstalt für Straßenwesen (BASt): Geschwindigkeiten auf Bundesautobahnen in den Jahren 2010 bis 2014
• Landesbetrieb Straßenbau: Auswirkungen eines Allgemeinen Tempolimits auf Autobahnen im Land Brandenburg
• European Commission: Going abroad - Speed limits
• European Commission: Traffic Safety Basic Facts 2018 – Motorways

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As always, do let me know if you have feedback, suggestions, or questions. I am looking forward to hearing from you! You can get in touch with me via simon@datawrapper.de, Mastodon, or Twitter.