decars1-9, Exercise 3: True figures, different conclusions

Model answer (check the method):

Why both can be accurate: the two sides compare different things. Opponents compare the Autobahn with other roads and show it is safer per kilometre driven. Supporters compare high speeds with lower ones and show that crashes at higher speeds are deadlier. Both statements can be true, because the Autobahn can be safer than country roads and still be made safer by a limit.

A fairer comparison:
1. Compare like with like: Autobahn stretches with a limit against similar stretches without one, controlling for traffic, road design and weather.
2. Look at before-and-after studies where limits were introduced or removed.
3. Compare with other countries' motorways, noting differences in traffic and vehicle age.
4. Measure the same outcomes (deaths and serious injuries per distance driven), not a mix of measures.
5. Check who funded and wrote each study.

Result: the evidence tends to be strongest on the safety effect for specific stretches and more uncertain for the network as a whole, and the decision also turns on values (freedom, climate, risk) that statistics cannot settle.