The world is on the brink of the biggest transformation in transportation since the invention of the internal combustion engine. Self-driving cars are no longer the stuff of science fiction but a rapidly advancing technology whose impact on cities may be greater than we can currently imagine.

According to forecasts generated by various artificial intelligence models and transportation analyses, the widespread adoption of autonomous vehicles could increase traffic volumes on city streets by roughly 30 to 50 percent. If that scenario materializes, a four-lane road may no longer be sufficient in the future, with capacity needing to expand to the equivalent of six lanes. Likewise, a major highway that now has three lanes in each direction may eventually require five lanes in each direction.

The reasons are straightforward. A self-driving car no longer has to wait in a parking lot or driveway. It can drive to pick up its owner, take the children to school, then head to pick up another family member or travel on its own to its next assignment. Every such empty trip adds more vehicle miles traveled. Even if the total number of cars does not increase significantly, the burden on city streets could grow substantially.

The largest share of public transit users consists of people who rely on it out of necessity rather than preference, such as young people who do not yet have a driver's license. This group stands to benefit the most from autonomous vehicles, since they would be able to travel independently and safely without a license. It is reasonable to assume that a large share of them — estimated at more than 70 percent — would choose personal transportation over public transit under those circumstances.

Another major user group consists of older adults, for whom convenient door-to-door travel is the highest priority. If autonomous transportation becomes significantly cheaper than taxi service, a substantial share of this group as well — estimated at 50 to 60 percent — could prefer self-driving vehicles to conventional public transit.

If these developments occur, public transit in Estonia could lose more than half of its current ridership. That would fundamentally alter the traffic models and assumptions on which cities and transportation infrastructure are currently planned.

Unfortunately, urban planning in Estonia is often moving in the opposite direction. Instead of preparing for future traffic volumes, many places are reducing the capacity available for automobile traffic. If autonomous vehicles become widespread at the pace currently forecast, today's decisions could prove inadequate within just a few decades.

If traffic volumes increase to the extent projected by multiple forecasts, rebuilding individual intersections or optimizing traffic signal timing will no longer be enough.

Tallinn needs strong transportation arteries — fast primary connections that function like the arteries of the human body. The heart could not supply the body if its arteries were replaced with veins, and the same principle applies to urban traffic. If the main transportation corridors become slow, fragmented or too limited in capacity, the city itself begins to suffer and decline.

Whether these transportation arteries follow existing major roads, pass through neighborhoods or are built partly along new routes is ultimately a matter of planning. What matters is that they provide enough capacity to meet future transportation needs.

At the same time, not every mode of transportation has to share the same street space. Pedestrians, cyclists and green spaces also need uninterrupted networks of their own, which do not have to run alongside roadways. When every mode of transportation is given space suited to its purpose, mobility, safety and the overall quality of the urban environment all improve simultaneously.

Urban planning and street network design are investments that last at least half a century. New buildings are designed with a 50-year service life, but they often remain in use much longer. The same is true of streets, intersections, bridges and the urban environment as a whole. That means every decision made today will shape how people move around cities well into the middle of the next century.

If we design cities around yesterday's traffic model, we may discover that the infrastructure we build no longer meets society's actual needs. The purpose of urban planning is not to react to change after the fact, but to anticipate it.

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