How is vehicle speed measured?


#1

I was looking at the GTFS realtime feed and noticed a bus doing 101km/h down Broadway in the city, which seems highly suspicious… you wouldn’t have enough distance to get a bus up to that speed, let alone with traffic and red lights!

Is speed data gathered from GPS readings (which can be inaccurate) or directly from the vehicle’s speedometer? In what ways can speed data be erroneous? Generally it looks very plausible.


#2

Hi @timbennett,

Speed data for bus real time feeds is captured from GPS readings in the Opal machines. The data may be inaccurate due to various reasons such as network problems or malfunctioning/faulty machines. If you have a specific example please let us know so we can look into it further.

Thanks.


#3

Thanks Alejandro, that sounds easier than hooking into the bus’s speed measurement. I think the high measurement I saw was just a one-off in a built-up environment where GPS can be unreliable, but if I ever notice a service returning consistently high readings I’ll flag it.