Not-so-short cuts: how humans are terrible at navigating cities
New research from MIT suggests that rather than taking the shortest path to our destinations, humans regularly make take longer routes, particularly ones that face towards our endpoint. Helen Collins investigates why we are so inefficient at navigating and how this approach evolved.
We are all too familiar with the stress of navigating around a new city. Even hardened city-goers will recognise the feeling of running late to a meeting or event and trying to work out the fastest way to get to an unfamiliar place. Yet it always seems to take longer than you’d planned.
Well, you’re not alone. New research published in the journal Nature Computational Science last month found that humans are naturally very inefficient navigators, often taking longer routes than necessary to reach our destination. The study, led by Professor Carlo Ratti at MIT, used GPS data from over 14,000 people as they travelled around two major US cities: Boston and San Francisco.
The authors applied several computational models to work out how the participants planned their routes. Surprisingly, people rarely took the shortest possible route.
“Instead of calculating minimal distances, we found that the most predictive model was not one that found the shortest path, but instead one that tried to minimize angular displacement — pointing directly toward the destination as much as possible,” said Dr Paolo Santi, a co-author of the paper. The scientists termed this approach as “the pointiest path”. Known technically as “vector-based navigation”, these findings suggest our brains like us to face towards our destination, but this makes us take more convoluted routes.
Prof Ratti was also interested in whether people take different routes to and from specific places, called “asymmetric navigation”. Writing in The Conversation, Ratti recalls: “Twenty years ago, I was a student at the University of Cambridge, and I realized that the path I followed between my bedroom at Darwin College and my department on Chaucer Road was, in fact, two different paths.” Was it just him that did this, or do we all make similar asymmetrical journeys?
The new results confirm how we tend to travel. It also agreed with previous studies showing that we often use key landmarks in our journey to navigate. Moreover, we often underestimate how long roads are, leading us to take lengthier routes.
Summarising the findings, Prof Ratti said: “Based on thousands of walkers, it is very clear that I am not the only one: Human beings are not optimal navigators.” Why, then, did this mode of navigation evolve, rather than one which could save us time?
One hypothesis is that we simply aren’t used to living in big cities. For most of human history, people lived in rural communities. If you wanted to go somewhere new, you simply walked towards it or used landmarks such as mountains and rivers to guide you. Of course, this is very different today; we have so many more obstacles to avoid.
According to Prof Ratti: “In the savanna, calculating the shortest route and pointing straight at the target would have led to very similar outcomes. It is only today that the strictures of urban life — traffic, crowds, and looping streets — have made it more obvious that people’s shorthand is not quite optimal.”
Thus, there is a conflict between reaching our goals quickly and saving energy. By taking the shortest route we might take less time travelling but we may expend a lot more mental energy planning our route. So, a system that can get us close to the shortest route but is easier for our brains to compute is optimal.
“It is only today that the strictures of urban life — traffic, crowds, and looping streets — have made it more obvious that people’s shorthand is not quite optimal.”
Of course, this research is far from exhaustive, as the authors point out. For one thing, they didn’t have any information about the journeys apart from their GPS routes. There may be other factors affecting how we plan routes, such as the time of day, how busy the roads are, or if we want to avoid certain parts of town. More research is therefore needed into the decisions we make when planning our journeys.
This is an important finding for the field, as well as for those of us who are perpetually running late. It gives us new insight into how people use cities, which will help to design cities to better meet the needs of the population. This could include pedestrian-only routes that better suit our needs such as safer and quieter footpaths.
So, next time you’re trekking out-of-town or traversing a busy high street, just remember your brain simply didn’t evolve to deal with these situations. And don’t be fooled by your natural sense of direction, you may be taking a not-so-short cut after all.
