It clogs systems, causes accidents, wastes energy and makes people unhappy. It’s more than a bad experience on a website — in cities, bad user experience (UX) design can actually kill. We’re talking about signage, public spaces, civic and emergency communications and other forms of urban design that influence our daily routines and, in some cases, are there expressly for our safety.

As more parts of our cities go digital, we have the opportunity to make cities not just safer and more functional, but more human, intuitive and enjoyable with UX that’s responsive to the world around us. While bad UX can cause anxiety, confusion and even injury, great user experience design can create efficiencies, keep us safe, get us where we are going faster and turn everyday city drudgery into moments of discovery, surprise and enjoyment.

Driving change in cities, with all their heavy infrastructure, mega-scale projects and regulations, can seem stifling and impossible. But by focusing on simple design adjustments on top of existing infrastructure, we can make huge positive impacts more nimbly, on shorter time frames and often with much smaller budgets.

Great experiences don’t have to be complex: One of the greatest innovations in transit user experience in the past 50 years is not the autonomous car or the hyperloop, but rather a sign on a train that says “Quiet Car.” This simple piece of vinyl has an immense ROI, having made a positive impact on hundreds of thousands of commuters, allowing them to catch up on precious sleep or focus intently, fundamentally altering commutes from lost time into productive hours.

The Pentagram-designed “LOOK!” warnings painted on the street at crossings is another lightweight, ingenious improvement. Its eyes prompt you to look the way they are pointing, and have likely saved countless cell phone zombies and tourists from getting run over by a taxi or bus, not to mention clearing the way for city emergency response resources.

A poorly designed train platform can cause fatal accidents on a busy day.

And Janette Sadik-Kahn’s famous Times Square revolution here in New York transformed one of New York’s most famous landmarks. With little more than some paint, some lawn chairs and some cement flower boxes to protect pedestrians from vehicles, she turned a busy street into a pedestrian plaza. In cities across the world, mayors and planners have built on this model, turning streets into parks, closing them down to cars, opening them up to human interaction and improving the quality of life for residents and visitors.

Digital technologies interfaced with the physical world give policy makers new tools to shape outcomes in response to on-the-ground conditions — think digital signs or physical actuators like movable barriers or lighting that can be pre-programmed and change in response to events in the environment.

With this flexibility, city leaders can optimize for different outcomes at different times, while still using the same principles of our analog tools. We still need to See, Think and Act, but updated for a digital context, we need Data, (Artificial) Intelligence and Programmability.

In the analog world, we use humans with clickers to count traffic. Now, we have access to massive data sets from mobile phone location services, as well as the rapid instrumentation of cities with computer vision and environmental sensors to understand on-the-ground conditions in real time.

The possibilities of a digital urban UX isn’t all about machine-driven, cold mathematical efficiency.

In the analog world, we had urban planners limited by access to data and their ability to model outcomes in complex city systems. Today, processing billions of real-time signals from our sensors, mobile devices — and relevant historical data sets — can support and inform action toward a desired outcome. Leveraging artificial intelligence from emerging systems like Google’s DeepMind or IBM’s Watson, these systems may identify alternatives we haven’t even thought of yet.

With the flexibility of a digital infrastructure, we can act on data-derived insights and test UX hypotheses in real time. We can make meaningful but reversible tweaks to the built environment by changing a digital sign, traffic signals or even controlling actuators to modify space or real-world infrastructure like escalator direction.

The feedback loop has improved, too. We used to have one-time community meetings or rarely answered surveys. Now, sensors and data sets can allow us to measure the impact of our intervention implicitly, allowing city dwellers to vote with their feet without compromising privacy — and enabling quick edits to improve algorithms and future outputs.

Linking with city systems data from traffic cameras and mobile apps like Google Maps or Waze could change the direction of one-way streets and open highway shoulders to temporarily ease traffic. A block party nearby wouldn’t slow things down; it would be accounted for and routed around. The same sensors and apps that detected the traffic could help inform whether the interventions were working, improve algorithms and know when to revert things back to normal when the rush was over.

Now, what if we could use these same tools to manage demand of the city itself? What if we could move people off culturally imposed peak cycles rather than build for them? Could we could do more with less?

The possibilities of a digital urban UX isn’t all about machine-driven, cold mathematical efficiency; it is also about people and human values. These tools can be used to make a more beautiful, friendly city. One that accommodates varying needs, languages and abilities. One that adjusts to make things more comfortable, more familiar, more festive or more exciting.

It’s time to turn the practice of UX to cities. UX designers will have a lot to do — figuring out what to optimize for and how to do it ethically will be a critical task. With millions of people, billions of pieces of data and thousands of touch points, what do you optimize for? Safety, speed of travel, enjoyment, economic improvement, discovery? How do you avoid the stale cycle of Amazon or YouTube recommendations?

As we build more hooks from the digital into the physical world, we’ll have greater programmability, new kinds of experiences and countless, subtle ways to optimize city life. Figuring out what to optimize for may be the biggest question of our time.