ISB1101: Identifying Buses

Every vehicle has a number plate, ISBs included. It is very simple. A few letters, a few numbers and a checksum letter. Later, I will explain the true meaning of the checksum.

Our ISBs have an interior number plate in the front of the bus, above the windscreen. It is meant to aid in identification of the bus should there be any incident or fault.

So when there is any problem with the bus, please just include the bus number plate inside your report! I always thought this was common sense, but NUSSU and OCA have always received a fair number of complaints that contain no identification of the bus whatsoever. If we are lucky, we can get the bus route, or timing. But evidently some people just hop on whatever bus comes to the bus stop, if they are taking a short ride.

With the Covid-19 situation in Singapore, I would also advise regular ISB passengers to make use of the interior number plate to note down which buses they have taken – I believe that the risk of getting infection from public transport is low if you take the right precautions like washing hands and not anyhow touching your face. But if we all record roughly what vehicles we were in, at worst it helps contact tracing, at best it gives you peace of mind if it turns out you didn’t ride with an infected person.

Reporting a bus

For any given route, there are usually between four and six buses that are doing that route for the week. Our longest ISB routes take less than an hour to complete, aside from BTC1 or BTC2. So if you specify merely the route and a one-hour period, chances are all the buses on that route will have been on the roads within that hour!

When submitting a report, it is of course helpful to give as much information as possible. Bus driver names are usually not identified inside the bus, but the number plate is mounted inside, as well as at the front and back of the bus exterior.

Students may report a bus for any number of reasons. It could be compliments or complaints about the driver’s behaviour, but also reporting of mechanical faults with the bus itself. If a seat is broken, or the bus stopping bell does not work, we would appreciate if students can report the fault to OCA supplying the bus number plate. It would save us a lot of CSI work!

The checksum

Earlier I promised to explain why the checksum is important. A checksum refers to a character appended to a sequence that is generated by an algorithm based off the other characters in the sequence.

To insert a bad Computing joke: “a checksum is basically a sh*tty hash function”. It takes in the existing string of characters and maps it to another character.

Many people have the misconception that Singapore number plates use a checksum to avoid forgeries by criminals. That may have been an intention, but it does not pass muster these days, for the algorithm is freely available online and any budding car thief could simply generate a legit number and stick it on his car.

Besides, even if it weren’t online, if I wanted to slap a fake plate number onto a stolen car I could just throw a Malaysian number onto it, right?!

The purpose of the checksum is related to crime, yes, but in a different way. It mainly serves to aid in the reporting of incident vehicles, so if a member of the public reports a vehicle and is unable to remember the full license number, the authorities can piece together the number plate with the help of the checksum.

Applying this to an NUS context now. Let’s say there is a mechanical fault with a bus that you were on, but you cannot recall the full number plate. You only recall it started with PC, and there was a 3, a 6, a 7 and an 8 or 9 in there.

We have quite a few buses, as it turns out, with those digits in the plate! Our Volvo B9L buses, registered in 2015, are mostly in the high PC3xxx to low PC4xxx series. There are five possible contenders: 3769, 3867, 3876, 3957 and 3967.

However, if you know the checksum, it would help narrow down the bus alongside other information.

PC3769’s checksum is R. It runs on D1/D2 and is white.

PC3867’s checksum is also R. It runs on A1/A2 and is orange.

PC3876’s checksum is P. It runs on B1, B2, C, BTC1 or BTC2 and is orange.

PC3967’s checksum is K. It runs on D1/D2 and is orange.

See how the checksum can distinguish 3769 from 3967 and 3867 from 3876?

Why are some number plates so short?

We have two buses with special number plates – PA2A and PA33K. These buses are used by our senior bus captains. While they’re in their office, their buses are used by other drivers for peak period fleet support.

Relax, the numbers were previously owned by the same company (ComfortDelGro) so it’s not like NUS spent a bomb on buying them; CDG just had to transfer them over, which costs significantly less than buying number plates as there is only an administrative fee.