There’s a curious anomaly with Apple Maps and Google Maps that took me a while to understand.

I live in Beach Haven on Auckland’s North Shore. Travelling from here to the Auckland isthmus is straightforward for 21 hours of the day, but between 6:30 and 9:30 am, car traffic is congested to the point where it can take 90 minutes, even more in the worst case.

The same car trip at other times might take 20 to 25 minutes.

Bus trips to the central city, Ponsonby or Newmarket are easy thanks to a much improved network that whisks passengers down Onewa Road and over the bridge in minutes. It doesn’t make sense to use the car in these cases.

For travelling almost anywhere else a car is essential. Multi-leg trips on public transport are possible, but often not practical. In some cases there’s no sensible return option.

So car it is.

And that’s where the digital maps get weird. This applies equally to Apple and Google Maps.

Ask, say, Apple Maps for the travel time from Beach Haven to Greenlane Clinic. Outside the rush hour it’s 30 minutes. No problem.

In the rush hour the app tells me the travel time is 38 minutes. Yet, when I attempt the trip, 38 minutes after leaving home I’m still only halfway down Onewa Road.

Why are both maps consistently wrong about travel times for this and similar trips?

My theory is that the maps get travel time data from phones. Phones sitting in cars move along roads like Onewa Road at a snail’s pace. But these are massively outnumbered by phones whisking along Onewa Road on the buses. Google and Apple don’t know if a phone is in a car or a bus, so the aggregate data shows travel times that aren’t possible in a car.

That’s my theory. If you have a better one, please share.