I recently began to notice a disturbing trend of automotive and even regular “journalists” claiming that speed limits are too low and that safety would be improved by increasing them. This disturbing misinformation is based on 30-year-old research and most concerningly promotes the dangerous perception that speeding is anything but morally reprehensible.
The research on which this claim is based was largely conducted prior to increases in the speed limits in the 90’s. With a baseline speed limit of somewhere around 55 mph, researchers determined that few motorists actually follow the speed limit and the consequences of slightly exceeding the limit are small compared to the increased risk of some drivers speeding and others driving slower. Based on this, the DoT adopted the 85% rule by which speed limits are set in part based on the actual speed drivers choose to drive rather than road design to minimize the speed differential between slower and faster drivers.
Today, we have speed limits in excess of 80 mph in some states and with the benefit of hindsight can evaluate the real-world consequences of increasing speed limits. Furthermore, in 30 years researchers have come a long way and developed much more sophisticated methods to measure the relationship between speed and traffic accidents.
In the early 2000’s, the DoT began to look at what the effects were from years of increasing speed limits. While some studies appeared to show increased speed limits may have decreased the rate of minor accidents, the rate of serious or fatal accidents had increased.
(Newer research taking road conditions into account in addition to speed (such as approaching an intersection or curve) has since shown that the methodology of the research showing higher speeds decreased minor accidents is likely flawed. Higher speeds increase the risk of all accidents, minor and major.)
In 2017, the NTSB put out a report on the effect of high speed on traffic safety. In it, they point out that higher speeds increase the energy involved in an accident, increase the risk of high-fatality accident types (ex road departure), and that many fatal accidents involve vulnerable road users such as cyclists or pedestrians.
The EU publishes a summary of current research on speed and traffic accidents. They point out that not only does speed increase the risk of serious accidents, but that the increased risk of an accident when some motorists drive faster than others on which the 85% rule is based is primarily due to the increased risk the speeding motorist will be in an accident, not the slower one. They also point out that higher speed limits mean unexpected road conditions are more likely to exceed the capabilities of a vehicle or driver.
To drive the point home, both the EU and NTSB point to Australian research that speeding even modestly is comparable to drunk driving in increasing the risk of a traffic accident.
The IIHS also points out that due to the adoption of the 85% rule, speed limits have crept up beyond the scope of even the flawed research on which it was based. Motorists who exceeds the speed limit by 5-10 MPH gradually cause the average speed of traffic to increase every time a road is surveyed.
Hopefully, the DoT will base their decisions on science and not libertarian propaganda. The NCUTCD has recently voted to ask the DoT to all but eliminate the 85% rule and base speed limits on road conditions, not whatever reckless speed some drivers choose.
Ironically, higher speed limits probably actually slow down traffic. Finnish research shows that during peak traffic hours, when most people actually commute, speed limits of about 40 kph (~30 mph) allows faster flow of traffic than higher limits. Therefore even in the name of convenience a lower speed limit makes more sense than a higher one.