To drive innovation, phase out speed limit signs.

We need better transportation infrastructure. In the case of automotive roadways — which is in a sorry state in America — better should include:

• Increasing safety
• Enabling innovation
• Reducing carbon emissions and other waste
• Lowering cost

A small way to start accomplishing all four of these improvements is to phase out roadside speed limit signs. Instead, speed limits should be posted in an authoritative database. That speed limit from that database can then be displayed to the drive on a vehicle dashboard or phone navigation app.

Increasing safety and enabling innovation

Currently, companies have to build or license their own maps. The dependent product can only be as good as the map upon which it is built — remember when Apple Maps was directing people to drive across active runways? Autonomous vehicles, traffic optimization algorithms, delivery services, and industries not yet dreamed of all require accurate digital maps.

We need companies to innovate on how they use maps to navigate and explore the world, not spend time recreating the map itself. We should consider an authoritative digital map a critical piece of transportation infrastructure. Eliminating physical speed limit signs is a perfect forcing function for the adoption of this digital roadmap because it requires the map to be authoritative, it eliminates the need for autonomous systems to waste effort using machine learning to read speed limit signs, and it requires a review of the speed limits themselves.

The availability of the digital maps and speed limit data would also allow for academic research into all manner of transportation problems. This would include mitigating risk at intersections or roads with frequent accidents, alleviating congestion, and reducing fuel consumption. As more data becomes layered in with the map — as it inevitably would — research would expand to inform public policy, public transit design, and numerous other decisions.

Digitally broadcasting and displaying the speed limit is a boon to safety. An always-visible speed limit would reduce instances of a driver not knowing what the speed limit is. As autonomous vehicles become more prevalent, it would eliminate the risk of a vehicle’s camera misreading a speed limit sign. Eventually, speed limits may be adjusted in real time based on traffic or weather conditions.

Reducing waste and lowering cost

I estimate there are well over 9 million speed limit signs nationwide. While there is no national standard for spacing between signs — each state sets their own — the National Committee on Uniform Traffic Control Devices MUTCD recommendations provide good baseline for estimates. For example, Freeways should have a sign after every interchange and every 25 miles thereafter. Meanwhile, Urban Collectors should have the limit posted every quarter mile.

Applying those distances to the 4.2 million miles of roads tracked by the Bureau of Transportation Statistic’s Public Road and Street Mileage yields approximately 8.2 million signs based on mileage. It’s difficult to estimate the number of interchanges, intersections, or limit increases or decreases that require more frequent posting, but rounding up to 9 million is still an underestimate, if anything.

The cost to install a single sign varies based on size and distance from an urban center. I also don’t have access to the contract bids from construction companies. But if an MUTC compliant 40 MPH Sign cost $79 and a bulk order of a highway-sized signs cost $133 each, then let’s say $100 per sign. Add the cost of steel for the post ($120), concrete for the base ($5), and labor ($50)… that’s around $275 per sign.

So $2.5 trillion tied up in speed limit signs, give or take.

Not to mention 15,000 tons of aluminum and 61,000 tons of steel. These are super rough, probably comically low estimates. And yes, I realize that has been invested over decades, not all at once. Annual upkeep is still probably in the millions of dollars, as signs are damaged or wear out. New roads are always being built as well.

As I’ll discuss below, a digital map would cost orders of magnitude less. But think of what could be built with all of that metal tied up alongside roadways… enough aluminum for 576 Boeing 787 Dreamliners... enough steel to rebuild the towers of the Golden Gate Bridge, with some to spare.

Comparison to OpenStreetMap

OpenStreetMap is a community-maintained global map database. It is supported by a nonprofit registered in the UK, The OpenStreetMap Foundation. It is the best freely available database of roads (as well as trails, railway stations, and more).

OpenStreetMap uses Protocol Buffers, designed by Google, to encode data. This format makes it is easy to export data, build routing applications, or conduct other analysis. Maps can even include legal speed limits with the maxspeed= tag.

An official government map is the only way to make the map truly have authority. Literally, a law could be passed which makes the Government’s database of speed limits on roads the speed limit for that road.

While these are many of the features that a government-sponsored solution must also have, a government sponsored database would not be redundant.

For starters, a non-profit, volunteer supported organization can only expect be expected to have limited accuracy. More importantly, OpenStreetMaps can only use what data is available to the public. An official government map 1) would force improvement of data quality and 2) is the only way to make the map truly have authority. Literally, a law could be passed which makes the Government’s database of speed limits on roads the speed limit for that road.

The OpenStreetMap Foundation’s Treasurer’s Report shows a 2020 total operating expense of £174,138. This includes hosting fees for the map servers as well as a slew of administrative expenses.

After converting from GBP to USD and increasing the expenses by an order of magnitude to account for employee salaries and bureaucratic overhead, cost to maintain the country-wide database would still be less than $2.5 million annually. That number feels small to me, but even doubling our tripling it is a far cry from the trillions currently invested in speed limit signs.

Secondary considerations

As with any revolutionary change, it is absolutely imperative that secondary and long-term impacts are considered.

• Insurance companies may track if someone is speeding. But this is already happening with Safe Driving Apps, which track miles driven, time of day, how fast you drive, quick stops or turns, if you are using your phone, and more. So really the only difference is the degree of certainty the insurance company has about what the speed limit really is. That actually might be a good thing for consumers — if they are still so inclined to install that type of surveillance on their device.
• Every vehicle would be forced to connect to the Internet. Again, this is already on the rise as safety features, remote start, updates to firmware, and other benefits increasingly encourage vehicle connectivity. If truly every vehicle was forced to have a connection then there would be increased demand for manufacturing the chips and antennas (something the industry is already struggling with) and the ever present cyber security concerns. Auto companies would then be further encouraged to collect and, probably, sell data of your whereabouts and driving habits. Implementing this policy would increase the urgency of privacy concerns, but these concerns are already present; if anything, it would bring them to better light.
• Owners of older vehicles would be reliant on their phones. As speed limit signs are removed or not replaced, if you drive an older vehicle your phone would be the only way to know what the speed limit is. In order to safely see the limit you would need to mount the phone to the dashboard, which is less than ideal. Likely, vehicle manufacturers would begin to redesign the dashboard to easily display the speed limit to the driver.
• This would set the foundation for digitization of other signs. Once migrating to digital speed limit signs proves successful, other signs could be included. For example, digital Steep Grade signage could help semi-trucks with route planning. Long-term, digitization of all signs would be hugely beneficial for autonomous vehicles.
• It burdens local governments by forcing modernization. For rural counties or municipalities in particular, the expertise and budget to create a digital map would be challenging. Federal funding would likely be required to assist the transformation. However, while some cities are independently moving towards digital records, these local governments would not be able to on their own; this gets them the benefit of digital records sooner.

Conclusion

Implementing a government sponsored digital roadmap that includes authoritative speed limits would allow for phasing out physical speed limit signs. Removing the signs themselves would take years to gradually accomplish, but the benefits to innovation, safety, carbon emissions, and cost would be quickly realized. There would be some growing pains as vehicles become increasingly connected and local governments have to modernize. Security and privacy concerns will continue to increase regardless, so it is better to be intentional in addressing them and seize the benefits a digital roadmap offers.