When you ride a bus, you might sometimes hear a loud “Beeeeep, beeeeep” sound. Ever wondered why that happens?
If you’re someone who takes the bus regularly, you’ve probably been curious at least once. So where exactly is that sound coming from?
Korea’s BIS (Bus Information System) in 2001
Translated from Korean by AI
Note: This content was created in 2001 and may differ from the current BIS system. Please keep this in mind to avoid any confusion while reading.
The illustration on the left, though a bit crude, shows a simplified version of a device called a Tacho. You’ll find it above the driver’s seat, and under normal conditions it works as a clock.
But it’s not just an ordinary clock — the Tacho communicates with devices installed at key points along the road. Those roadside devices are connected to the central database system, where all the information is stored.
Each bus-mounted Tacho has its own unique ID number, which is recorded in the central database along with the bus’s route number and vehicle number. When the bus passes a certain location, the Tacho exchanges data with the roadside unit, and a record is stored. When the next bus passes the same point, a new record is saved, and the system compares it with the previous bus’s record to calculate the time gap. That information is then sent back to the bus, and the Tacho emits its “Beeeeep, beeeeep” sound to notify the driver of the headway to the bus ahead.
When you hear “Beeeeep, beeeeep, beeeeep”, it’s the Tacho giving you information.
For example, the number 38 means that the bus ahead is bus number 38, and the one ahead of that is number 37.
The gap to bus 38 is 5 minutes and 25 seconds, while the gap to bus 37 is 10 minutes and 10 seconds.
The first three beeps indicate the time gap to the bus immediately ahead, and then a single beep follows to give the gap to the “second” bus ahead.
If the scheduled headway for this route is 5 minutes, this situation would be considered perfectly normal.
In another case, the Tacho might show that the gap to the bus ahead is 7 minutes, and the one ahead of that is 12 minutes.
That would mean that the bus ahead and the one in front of it are keeping a perfect 5-minute gap, but your bus is running 2 minutes late compared to the ideal schedule.
Seeing this, the driver might decide to speed up a little to get back on time.
There are many variations of the Tacho in use. Next time you ride a bus, check the headway time posted on the destination sign before boarding, then watch the Tacho once you’re on the bus. You’ll be able to tell whether the bus is running late or if it’s actually ahead of schedule.
