In the United States, speed limit recommendations are typically designed to be “related to crash risk; provide a reasonable basis for enforcement; fair in the context of traffic law; and accepted as reasonable by a majority of road users.” But how these recommendations are chosen is based on dozens of potential criteria, including determining a speed which 85% of drivers won’t exceed; infrastructure conditions; minimizing travel time, traffic noise, and air pollution; and finally, injury minimization. It is notable that with regards to this final injury criterion, two transportation studies from the United Nations Economics Commission for Europe[2,3] show that collision above 70mph guarantees fatality, irrespective of posted speed limits.
Using this threshold of 70 mph for behavioral comparison, Drivemode reviewed the data of over 150K anonymized Android users in 2017, driving over 3.2 million miles and producing over 82.4 million points of anonymous GPS location data. With this information, Drivemode studied the incidence rate of drivers exceeding 70 miles per hour relative to overall driving sessions in each state.
"Drivemode's ability to analyze driving data at scale provides unprecedented insights into the behaviors of American drivers," said Yo Koga, co-founder and CEO of Drivemode. "In this study, tracking driving speeds in both absolute terms and relative to a benchmark reveals how driving trends could inform driver safety and lawmaking. That data provides a window into how effective posted speed limits are in prompting drivers to maintain safer speeds.”
Nationally, 9 states have a maximum speed limit under 70 mph, 23 states have a maximum limit of 70 mph and 18 states exceed 70 mph, with the highest posted limit of 85 mph in Texas. Using over 55 million GPS location points and over 7.2 million data points of speed from 71 mph and above, Drivemode determined that on average, American drivers exceed 70 mph during 13.13% of their drivetime.
The graph below shows the state-by-state percentage of drivetime exceeding 70 mph in red and the corresponding legal maximum speed limit in light gray.
States With Highest Percentage Of Drivetime Exceeding 70 mph
#1 Wyoming: 21.09% (max limit 80 mph) #2 South Dakota: 17.07% (max limit 80 mph) #3 New Mexico: 16.50% (max limit 75 mph) #4 Kentucky: 15.71% (max limit 70 mph) #5 Alabama: 15.43% (max limit 70 mph)
Overall, the data shows the percentage of time driving above 70 mph increases as the state maximum speed limit increases; however, there are notable exceptions to this trend which confirms that driving behavior is informed by more than posted speed limits alone.
States With Max Speed Limit of 75 mph+ And Low Percentage of Drivetime Exceeding 70 mph
#21 Nevada: 10.45% (max 80 mph) #22 Texas: 10.43% (max 85 mph) #28 Idaho: 9.75% (max 80 mph) #33 Maine: 8.26% (max 75 mph) #34 Colorado: 8.24% (max 75 mph)
Despite high speed limits, drivers in some states prefer to drive at speeds that are more moderate. Among states with a max limit of 75 mph, New Mexico (#3) is driving 16.5% of the time above 70 mph whereas Colorado (#34) is driving half of that time at 8.24%. Though these two states are in the same region of the West with the same 75 mph maximum limit, New Mexico is more rural—its population density is only 17.2 people per square mile compared to Colorado’s 50.8—so its roads may lend themselves to speedier driving. Texas is also noteworthy for having the highest maximum speed limit of 85 mph, but sits in the middle of the pack at #22, with drivers spending only 10.43% of driving time above 70 mph.
Top States Most Frequently Exceeding Max Speed Limit of 70 mph
#1 Kentucky: 15.71% #2 Alabama: 15.43% #3 Mississippi: 14.65% #4 Iowa: 13.08% #5 West Virginia: 11.87% #6 Wisconsin: 11.87% #7 Tennessee: 11.47% #8 Missouri: 11.13% #9 South Carolina: 10.37% #10 Georgia: 10.25%
Of the 23 states that have a 70 mph maximum speed limit, the list above shows the top ten states where drivers are most frequently exceeding that limit. Though posted limits are legal benchmarks, from state to state and even road to road, communities have contextual experiences of how “official” posted limits truly are. In some places, 5 mph above a posted speed limit is culturally accepted, whereas other groups may embrace 10 or 15 mph above the limit.
“I believe we will see that as more autonomous vehicles share the road, issues of determining speed limits and their enforcement will require more scrutiny,” said Koga. “Drivers frequently exceed posted speed limits to keep up with traffic flow. However, if an autonomous vehicle is required to drive at the posted limit, it may become a danger within faster traffic flow. We already see how autonomous driving features like Tesla's autopilot had to increase driving speed beyond the legal speed limit; their cruise control is called ‘Traffic-Aware Cruise Control.’ Software developers are defining the meaning of the ‘speed limit’ through these choices. Perhaps when autonomous cars are the majority of vehicles on the road, safer speed limits can be more easily standardized and consistently observed.”
Notably, drivers in Massachusetts (#35) and New Jersey (#37) speed like they’re on roads in states that are far more rural. Both Northeastern states have a maximum speed limit of just 65 mph, yet they have a higher percentage of dangerous driving time relative to the 70 mph threshold, at 8.19% and 8.03%, respectively. Interestingly, they both rank near our previous example of Colorado (#34) for incidence rate above 70 mph, however the population density of Massachusetts is 858 and New Jersey is 1210 per square mile.
Below are the 50 U.S. states, ranked by percentage of time spent driving over 70mph, out of overall driving time.
|Rank||State||Region||Percentage of driving time above 70mph||Maximum Speed Limit||Population Density Per Square Mile|
Data cleansing included conversion of raw data of meters per second to miles per hour and rounding to integers; removing outliers, invalid data, and erroneous GPS locations; capping dating at erratic or possibly unrealistic gps report of speed (eg: exceeding 125 mph). Quality checking included GPS distribution checks and state latitude/longitude average map plotting tests.
- Methods and Practices for Setting Speed Limits: An Informational Report, Federal Highway Administration Safety Program.
- Consolidated Resolution on Road Traffic, Speed and Fatality Studies from United Nations Economics Commission for Europe (UNECE), p. 23.
- Intelligent Speed Assistance: Why Do We Need It?, Speed and Fatality Studies from United Nations Economics Commission for Europe (UNECE), p. 5-7.
- Governor’s Highway Safety Association speed limits by jurisdiction and speed limits by state.
- United States Population Density
- Insurance Institute for Highway Safety 2016 Fatality Facts State By State