Speed limits on German highways are a major point of contention, seen as a restriction on personal freedom by some, and as life-saving by others. But what is actually true? One scientist at Ruhr University Bochum, Germany, has compiled new, reliable data for the first time in about 50 years. The results show that a speed limit of 75 miles per hour (120 kilometers per hour) would reduce the number of crashes with severe injuries by 26 percent, and the number of traffic fatalities by 35 percent. The study has been published online in the journal Transportation Research Part A: Policy and Practice from August 5, 2025.

German highways are the Holy Grail for many fast drivers, because in no other European country is it possible to drive at unlimited speeds on many highway sections. Germany has so far relied on only a recommended speed of 81 miles per hour (130 kph). Although supporters of a speed limit point to safety and environmental protection, there is relatively little data that speaks for or against a speed limit. The last major study was conducted between 1974 and 1977, over 45 years ago, and vehicle technology and roadway construction have advanced considerably since then. At the time, researchers examined the effects of an 81 mph speed limit compared to only a recommended maximum speed. This experiment was conducted on nearly 1900 miles of highway. The study found that introducing a 81 mph speed limit reduced injury crashes by about 10% and fatalities or severe injuries by roughly 20%.

“Since no no suitable data for such an analysis previously existed, I compiled an entirely new data set from a variety of sources,” says Maike Metz-Peeters from the Chair of Economic Policy and Applied Econometrics at Ruhr University Bochum. This set covers about half of the entire highway network and spans the years 2017 to 2019. The dataset covers about half of the entire German highway network and spans the years 2017 to 2019. It provides data in 500-meter sections, including information on road conditions, traffic volume, weather, and regional factors. Since most sources are publicly available, an open version of the dataset has been released for reuse. “Nothing comparable has existed before,” says Metz-Peeters.

The data set was analyzed with a modern method of causal machine learning known as Causal Forests. These methods build on classical machine learning methods to allow causal effects to be estimated under specific assumptions. “In simple terms, the algorithm looks for road segments that are as similar as possible in the relevant characteristics and only differ in whether they have a speed limit or not,” Metz-Peeters explains. “Because segments with and without a speed limit differ systematically on average and because we can never fully capture all risk factors, such a comparison will always be incomplete.” To address this, the central assumption of the study is that segments with speed limits are on average more dangerous as comparable segments without a limit, meaning that if no speed limit had been introduced, they would have had more crashes than similar segments without a speed limit. “Characteristics that could violate this assumption—for example, factors that could lead to a speed limit even though they are actually associated with more cautious driving behavior and thus fewer crashes—are given special consideration and omitted from the prediction when necessary. Based on the data and the assumptions made in the study, the resulting estimates are conservative, and the actual effects may even be larger,” says Metz-Peeters.

Based on this data, the impact of a 75 mph limit can be estimated most reliably. The results show 9 percent fewer crashes with minor injuries, 26 percent fewer crashes with severe injuries, and 35 fewer fatal crashes as a result of a local speed limit of 75 mph. The study also indicates that speed limits are particularly effective at entry and exit, ramps, and on less frequented roadways. The latter seems surprising at first, but is in fact plausible: where there is less traffic, cars tend to drive particularly fast and with large speed differences, increasing crash risk. In heavy traffic situation, by contrast, high speeds are not possible anyway, so a limit has little effect. This result would contradict recommendations that speed limits should be flexible and lifted during low-traffic periods. “Because the estimated differences are only partially statistically significant, these indications should be more closely examined in further studies,” explains Metz-Peeters.

Extrapolated to all currently unrestricted segments of German highways, a limit of 75 mph would prevent approximately 53 fatal crashes with 58 casualties, 649 severe crashes with about 904 seriously injured, and 801 minor crashes with about 1375 lightly injured per year. The resulting savings in accident-related costs amount to about 216 million euros annually. “However, it’s hard to predict whether the results translate to a general speed limit throughout the entire highway network,” says Metz-Peeters. Driving behaviors may adapt and the number of crashes could decrease even further. “On the other hand, speed limits could also lose their signaling effect, because they specifically highlight dangerous areas. As a result, crashes on previously limited sections could even increase This can only be speculated and cannot be determined by similar observation studies or locally restricted experiments.”