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If you're driving in San Francisco one week and then New York City the next, you're probably not paying attention to the small differences in rules when it comes to sharing bikes lanes, passing school buses, and turning right on red.

If you're in a self-driving car, those state-by-state distinctions aren't just a nuisance (and potential ticket since ignorance isn't a legal defense), but rules the self-driving companies don't want to overlook, no matter how tedious. The software controlling the car needs to have those slight variations in traffic law programmed in, especially since companies don't want negative media attention or a blemished record showing it broke the law.

Self-driving technology company Aurora looked into regulations for autonomous vehicles (known as AVs) across 29 states and found that they can vary. California has one set of testing rules, while other AV-friendly states like Texas and Arizona have others.

But then you also have the general rules of the road that autonomous vehicles have to obey like any other car. Again, any sort of consistency across states is a pipe-dream. But for AVs, those rules are important, even if a human driver isn't likely to look up that California requires stopping for a school bus (but not on a multi-lane road.)

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Charity Allen, Aurora's regulatory counsel, wrote a blog post Wednesday calling for more consistent rules of the road when it comes to AVs. She argued that companies like Aurora with its self-driving software have to keep up with a clunky system that tracks traffic laws, plus update and maintain a constantly changing database to remain law-abiding and safe.

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"Programming individual state road rules into our system is challenging, but not crippling," Allen wrote. As AVs try to become more widespread throughout the country, a more consistent framework would be helpful for the companies building the software and vehicles. But different states and cities have individual needs when it comes to cars on the road based on weather, city layouts, population density, and other factors. It's not as simple as creating a uniform driving code.

Currently, self-driving cars are sticking to a few key states like California, Arizona, Pennsylvania, Michigan, Texas, Florida, and others. For the companies, it's easier to keep track of one state's idiosyncrasies.

Waymo, the Google self-driving car spin-off, accounts for different road rules at the mapping level. For its self-driving cars operating in 25 different cities in several states, detailed 3D maps incorporate rules specific to those streets and jurisdictions. Although the term "map" is used here, the information is not what you'd see on Google Maps. Instead it's a series of information like red-light rules, pothole locations, sidewalk lengths, posted signage, and more very specific details, like a city-specific law about speed limits in school zones.

Follow the rules! Credit: Smith Collection/Gado/Getty Images

Even finding the regulations for each state is an inconsistent experience. The literal "Rules of the Road" are tucked away into different manuals, codes, and handbooks across each state. Aurora pointed out how Arizona, California, and Pennsylvania each differently organize their vehicle and driver information.

Then you have the local city level, which adds another layer of complexity and opportunity for more law-breaking if those additional rules aren't tracked and plugged into the self-driving systems.

The U.S. Department of Transportation has yet to implement a nationwide policy for self-driving. Instead, it has a developing draft framework, "Preparing for the Future of Transportation: Automated Vehicle 3.0." The latest version came out in October and any hopes of Congress passing a self-driving car bill are waning.

Once a federal standard is set, expanding self-driving cars might happen quicker instead of stalling out at the state line.

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