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Autonomous Vehicle Infrastructure: Defining the Domain


Autonomous Vehicles: Still need a road to drive on.


While excitement has been building in recent years for having fully autonomous vehicles (AVs) on our roads, the delivery has proven to be challenging for many vehicle manufacturers. When the conversation surrounding AVs first started, many manufacturers focused on achieving fully autonomous vehicles (SAE Level 5), where human driving is eliminated.


That goal is still years in the future, but today’s drivers are already benefitting from many of the incremental steps the industry has taken toward full autonomy. And continued collaboration between private industry and the public sector is helping to deliver the technology and infrastructure improvements AVs will need to operate safely in more locations. Here’s a quick refresher on the AV levels established by SAE International, a global leader in developing standards for the mobility industry:

  • Level 0 represents no automation, much like a 1968 pickup truck.

  • Levels 1 and 2 include varying degrees of driver assistance features that are becoming increasingly common in today’s vehicles, such as adaptive cruise control, lane-keeping assistance, and emergency braking.

  • Level 3 represents conditional automation, in which the human must retake control when the vehicle determines it is no longer capable of driving.

  • Level 4 represents conditional automation in which the vehicle handles all driving functions within its operational design domain (more on this below).

  • Level 5 represents a fully automated vehicle. In terms of planning and designing for AVs, it is time to shift the focus to level 4 automation. Vehicles at levels 1 through 3 will have a minimal effect on transportation infrastructure design, and level 5 simply represents the most technologically advanced version of level 4. Preparing for this level of automation first requires a solid understanding of the operational design domain.

Finding the Use Case: What Is the Operational Domain?

The operational domain is the area in which level 4 AVs can safely operate. Vehicles that fit into level 4 of the SAE International scale will be able to provide completely autonomous functionality, but only in specific circumstances. How we define these circumstances or the operational domain for the vehicle, will determine how and where a vehicle can operate — and there are many ways to define that domain.


A domain could be defined geographically, such as a warehouse, a specific route, or an entire city. It could also be defined by roadway features, such as a dedicated lane or set of streets with highly precise GPS, well-defined lane markings, and high-reflectivity signs. It could even be defined environmentally, allowing the vehicle to operate only during the day or not in snow.

Level 4 automation is not incredibly difficult to achieve if the domain is strictly controlled. However, the trade-off is that the more strictly defined the domain, the less useful and applicable the vehicle becomes. Technically, level 4 AVs are already in use, such as farm tractors that follow a lead vehicle, automated guided vehicles in warehouses with specific paths, and airport people movers that operate on tracks in a separated right-of-way. These types of vehicles and their functions are not useful in all situations, but as their domains grow so does the complexity that the vehicles must be able to handle.


The Connecticut Department of Transportation recently received three level 4 autonomous buses; however, the operational domain of these buses is not entirely clear. Will they only be autonomous during docking — pulling up to the curb to pick up passengers — or will their operational domain include certain road segments or even entire routes? Since buses operate on particular routes and make predetermined stops to pick up and drop off passengers, they operate in a much smaller domain than most vehicles that operate in traffic. A private vehicle operating in the same city would require a domain that covers an entire region and many different routes for a wide variety of trips. With a dedicated and trained operator — such as in a bus — the vehicle could have a narrow domain in which to operate at level 4 but could operate at level 2 or 3 everywhere else.

To achieve more rapid deployment, some manufacturers have discussed designing domains to avoid certain complex situations. For example, if the domain were the entire city of Boston, the AV would likely encounter roundabouts and large traffic circles. If those roadway features are too complex for the AVs, the domain could be defined to avoid those features in Boston and provide alternative routes.


Preparing for Deployment: How Is the Domain Facilitated?

By determining where AVs can be most useful, and then defining domains accordingly, it is possible to deploy these vehicles in certain areas sooner and also inform how they will function in the future. At the present state of AV technology, significant infrastructure improvements will be needed to achieve broad level 4 deployments. These improvements may include physical separation, operating speed requirements, high-definition maps of the area, precise GPS, improved signing and striping, or any number of other site-specific or manufacturer-specific provisions.


Robust collaboration among vehicle manufacturers and transportation planners will be needed to design effective domains that incorporate the necessary technology and infrastructure improvements to support AV technology. And these improvements will work in concert with the adoption of connected vehicle (CV) and electric vehicle (EV) technologies, which compound the safety and economic benefits as well.


As we consider the many factors that impact AVs, focusing on the domains at the intersection of usefulness and readiness will bring the most value, making it clear that private industry and public-sector agencies will need to work closely together to make AVs a reality for more drivers, more quickly.


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