Fact check 50: “30% of accidents are caused by excessive speed”
“Speed is the problem.” We hear this often from NDOT engineers and TRPA/ CMP bureaucrats as justification for drastic speed reduction and reconfiguration measures of 4-lane US 50 that remove large sections of 2 lanes a way to slow traffic and “make it safer” by minimizing accidents.
But is it true? Does data support the claim that 30% of accidents are caused by excessive speed? Is speeding in fact the root cause of 30% of accidents along US 50 from Stateline to Spooner Summit?
Our Tech Team has taken a deep dive into the data to find out. Using original traffic accident reports from 415 accidents (2016-2020) and applying statistical hypothesis testing methodology to the reported data, we found that the claim of 30% of accidents caused by speed is false by a wide margin.
30% of accidents due to speeding would be 141 of the 415 total accidents reported. The data, however, shows that only 17 of 415 reported accidents can be attributed to unambiguous speeding, while another 33 are attributed to possible speeding. Taken together, these account for only 50 accidents where speed is a factor or about 12%—nowhere near the 141 needed to prove the 30% hypothesis.
Even when evaluated on a segment basis, not one road segment of the six along the corridor rises to the 30% of accidents caused by excessive speed standard.
Since speed is a factor in only about 12% of all accidents, road-diet and speed calming measures are not likely to improve road safety demonstrably. In fact, such constraints on traffic flow and congestion flow may aggravate the risk of accidents and driver frustration.
Conclusion
The NDOT/CPM hypothesis that speed is the problem must be rejected. Actual crash data invalidates this claim and premise for the elimination and reduction of lanes along our only fire evacuation corridor.
➡︎ For full report, see Statistical Hypothesis Testing Applied to US 50 Accident Data
