How do those countdwns at bus stops work? I know what they do, but HOW do they do it?

Question

Reason for asking is that they are so often wrong - sometimes the next bus arrives early, sometimes late, sometimes one arrives without ever having been shown.

Answer 1

This is complicated and you need to have some background information.

What you call "countdowns" is known in the industry as "Real Time" data transmission. "Real Time" has long been a feature on certain railways, where the problems are far less than on buses.

First, every journey on a bus timetable is entered into a computer database. The database includes the times passing certain points (known in the UK as timing points, or in the US, as nodes) and a unique identifier for the journey (usually called trip number or journey number). The database also knows the distance between each stop on the service and can therefore calculate electronically the expected time of passing each point.

This data is held, inter alia, on a central computer.

On the bus is an electronic ticket machine, which through a clever peice of hardware, is connected to an on-board transmitter.

At the start of each journey, the driver enters (amongst other data) the journey number for the trip into the ticket machine. (This process is also needed to access the faretable for that journey which is stored either within the ticket machine or, more often, the drivers' module.) As the bus proceeds, the driver updates the farestage as he passes each in turn.

As the bus continues on its way, it passes a number of receiving stations where the ticket machine data is interrogated and transmitted to the central computer. The journey number is compared to the master schedule and, on the basis of this comparision, calculates the expected arrival time at later stops. The journey number confirms the destination of the bus.

The central computer than transmitts this data to those bus stops further along the route. Dead simple!

But, there are problems. The central computer is only able to guage the extent of delay prior to the interrogation of the ticket machine data. It cannot crystal-gaze about what the bus is going to drive into. It might be heavier traffic (so that the estimates at later stops will be an underestimate), or it becomes traffic-free (so the bus appears to arrive earlier). You can't win!

Furthermore, despite what is claimed, ticket machines on buses are in a semi-hostile environment and data can get scrambled.

There are other operational difficulties, such as unscheduled short working, which add to the problem.

The above is just a very broad brush approach to a complex question, but I hope it helps.

Answer 2

Every bus has a tracker in it and every bus stop a reader.
Now lets say you're waiting at bus stop C for bus 1 and bus1 is at bus stop A. Now the reader at bus stop A picks up that it is Bus
1 is there and it is programmed that the estimated journey time to the next bus stop is 4 Min's and the next one 7 Min's. So with its Gps type devise it sends a signal to Stop B and it's sign says "Due" and a signal to Bus stop C and it's sign says 7 Min's.
These things are programmed to give the average time though and doesn't take traffic into consideration. That's why buses sometimes come earlier or later than the sign says.

Answer 3

each bus has its own helicopter
the helicopter follows the bus
and the pilot of the heliocopter uses a telephone
to call each of the bus stops
inside everybus stop
the spirit of the dead ancestors live
they have no earth;y abilities except the power to answer the telephone and work the display system
the reason some busses are not announced is
1 if the helicopter isn't working then they can't be announced - the most likley explanation
or 2
the spirit of the dead ancestors do not like you and deliberately set out to annoy you and thwart your travel plans
this is unlikely as these spirits know that they will be in lots of trouble if they start this again (its a long story)
so the helicopter has crashed (these stories are often covered up and do make the media)
or
more likely
the pilot is ill and has taken time off
there is actually a shortage of these pilots (being a highly skilled job)
and therefore there is little cover for illness
hope that helps

Answer 4

Automatic Vehicle Location technology (AVL) tracks the movement of 250 buses, giving up-to-the-minute, accurate information about bus location, traffic congestion and arrival times at 84 bus stops on the Quality Bus Corridor from Leith to Straiton. In turn, central computers relay this information to BusTracker signs across the city. This shows passengers exactly what time buses will arrive at their stop.
http://www.edinburgh.gov.uk/transportedinburgh/Buses/tracker/tracker.html
http://www.tfl.gov.uk/buses/ini-ibus.asp
http://www.uktelematicsonline.co.uk/html/vehicle_tracking.html

hope this helps :)

Answer 5

They just run according to the bus timetable in a lot of cases, or calculate the time since the bus left the starting point of its route - hence why they're wrong!

I know in London they're talking about installing a new system based on GPS which will be a lot more accurate.

Answer 6

No / oh hun i understand each and every time u see a female with long black hair you will think of this is me // yet u understand i do never wait on the bus end plus u gave me ur motor vehicle right this moment keep in mind?

Answer 7

No idea - we don't have such things out here in the sticks!
There's usually about an hour gap between buses round here and the post comes by pigeon.

Answer 8

sensors, just like at a drivethru for fast food