Ask Phoebe: GPS helps buses to run to timetable

AT says that the quality of the predictions has increased significantly over the past year. Photo / Brett Phibbs

I was wondering if you could explain how the electronic bus "real time" boards work?

It seems that these boards are rarely correct and I wonder how they get the buses' ETA? When a bus is overdue an asterisk replaces the arrival time. However, after a minute or so it disappears and the next arrival time shows.

When you ring Auckland Transport's number, the person on the line has only the same timetable information we can get online or at stations, etc. When you ask why they don't know where the bus is you are told that they are AT, not the bus company. Surely for our bus service to function well there needs to be some communication between the buses and AT?

Why can the electronic boards allegedly predict when the bus will arrive but a human who is meant to be providing that service can't? Why are the buses not on a GPS that AT can log in to and see where the buses actually are, not where the timetable says they are?

Apologies for the length of this, but yet again I and others have been left waiting for over half an hour with the "help centre" providing absolutely no help.

I cannot remember the last time I caught an Auckland bus that was on time.

Julia Newall, Herne Bay

Here's how it works. Buses are fitted with onboard global positioning system (GPS) equipment so they can be tracked on the bus route.

At the start of a trip, the driver keys the route number and departure time into the ticketing machine. As the bus travels along its route, predicted arrival times are sent to the electronic display boards at the bus stops. This information is relayed along the route as the bus passes set points, using information from the GPS.

"Due" means the bus is expected to arrive within two minutes. If the system can't find a service it knows should be starting, it displays the scheduled arrival time on the screens until the driver logs the service in. If after 10 minutes the service is still not logged, it shows as DLY (delay). As well, there is a GPS-based signal pre-emption process that lets bus drivers communicate their position to the city's traffic signals system.

If a bus approaches an intersection with signal pre-emption, the system can request traffic signal priority for the bus. For example, if the lights are green but about to turn red, the green phase can be extended by up to 10 seconds so that the bus can keep up with its schedule. If the lights are red, the green phase can be brought forward by 10 seconds.

AT says that the quality of the predictions has increased significantly over the past year because of new GPS units installed on all buses and 98 per cent of all buses are now tracked in the system.

Correction
The gun turret from HMNZS Taranaki was in the yard of Scrap Steel Recyclers, not Pacific Steel as stated last week. The error is regretted.