How Google Maps calculates your journey time – and plans ahead for traffic

We’ve all been there. Happily cruising along a familiar route when suddenly Google Maps suggests a detour. Should you take it, or stick to what you know? After all, the traffic looks clear up ahead.

Here’s a quick guide to how Google calculates journey time in the first place, and why it’s probably a good idea to follow its suggestions, even when it’s not immediately obvious why.

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How Google calculates journey time

This one is quite simple. Google knows the speed limit for pretty much every section of road you could be driving on, and uses this to determine the time it will take to travel on each section of road. It also tries to prioritise major roads that have fewer stops, for example roundabouts and junctions, as this further impacts travel time. This gives it a baseline journey time.

However, when you’re using Google Maps you’re providing anonymised data about your location and speed of travel, which the software can then use – combined with everyone else using Maps – to estimate a more accurate arrival based on the real-time speeds on each road.

How Google recalculates your journey – and why you should pay attention

Google has explained that if it sees traffic on your route, it can then create diversions to get you around the issue if its modelling predicts that will get you where you’re going sooner.

However, the calculations are much more complex than they sound. Google can tap into local government data to know about road closures and accidents, so it can avoid those locations, and this can be reinforced by other drivers reporting issues through the app.

Your route is also determined by historical data. For example, if you set a route and motorway traffic is currently clear, but Google knows that it’s typically much heavier at the time you would be arriving, it will automatically suggest a quicker alternative.

On top of this, there are plenty of rural roads in the UK with a 60mph limit, but Google will know if people typically travel slower to account for it being narrow or having unsighted corners. This will be factored into estimated journey times. In fact, Google was reporting that it used AI for these calculations way back in 2020.

Another factor that is taken into consideration is road quality – Google will try to avoid sending you down a dirt road or a narrow, winding country lane, even if it looks like a good idea on the map.

Why should I trust its calculations?

Well, unfortunately it’s impossible to know if you made the correct decision to take a detour or ignore it – unless you’re travelling with a friend and take alternate routes, of course.

However, in 2020 Google released a blog saying that its ETA predictions were correct for 97% of journeys. If you trust that number, then the answer is pretty clear: you should listen to Google Maps, even if it doesn’t immediately make sense.

It’s far from perfect, though. Traffic estimations are exactly that – estimations – and therefore if it warns that stopped traffic ahead will add four minutes to your journey, that could be inaccurate, particularly if traffic is building and the data lags behind reality.

If your priority is to get to your destination as quickly as possible, consider using Waze. Although it’s owned by Google and uses much of the same information, its routing algorithms are more focused on avoiding hold ups, even if that means taking less-travelled side streets. It’s much more effective in the city, where there are a lot of alternative routes to take, than it is in rural areas, though.

How to get the most out of Google Maps

You can use Google Maps straight out of the box and it will work perfectly fine, however there are a few ways you can optimise it.

The first thing to do is to go to your navigation settings and tell the app which fuel type your car is, from petrol, diesel, hybrid and electric. You can then ask it to prefer fuel-efficient routes, optimised to your type of car. If you don’t mind your journey potentially taking a bit longer to reduce your running costs, this is a great option.

You can also find parking near your destination to save you doing prior research. As you get closer, the app will display nearby parking and let you know how long it will take to walk to your destination. Once parked, you can tap on the blue dot that shows your location and select ‘save parking’, so you never lose your car again.

Also remember that you can see public transport routes for your journey by selecting the train symbol, which will list the best combinations of walking, train and bus routes to get you to your destination. You might find it’s quicker and easier not to take the car.

It’s a good idea to check official public transport journey planners, though. There are plenty of users complaining on social media about the app not allowing enough time for connections, for example.

How to make Google Maps better

If you find an error in Google Maps you can submit the problem online by following the appropriate link on this website. It lets you add or fix roads, report offensive or incorrect business information, and update addresses.

You can also help fellow road users avoid longer journey times. If you come across roadworks, an accident or police activity, all of these can be reported in the app. This helps warn others of hazards ahead, and potentially reroute their journey instead.

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