The Vehicle Location System (VLS) is a satellite-based bus tracking system. It makes use of a combination of a few technologies, including the Global Positioning System (GPS), to determine the position of the bus.

VLS operates through employing four main components on the bus:
i) A GPS Receiver, which provides vehicle location co-ordinates via satellite signals;
ii) A Distance Converter, which converts odometer pulses into distance travelled based on the odometer calibration constant;
iii) Configuration Data, which contains tables on fare stages of each bus stop, bus stop surveyed co-ordinates, inter-bus stop surveyed distance, odometer calibration constant and radius of certainty; and
iv) A Central Processing Unit, which compares the actual readings on the roads against the Configuration Data.

The fare stage of a bus is determined first by the distance travelled. This is carried out by the distance converter which converts the pulses recorded by the odometer to distance travelled. This data is then matched against the
pre-programmed set of Configuration Data in the system. If the actual readings match those in the Configuration Data, the fare stage will be updated accordingly.

When the bus pulls over at the next bus stop and opens its doors, VLS will also check the co-ordinates of its location, via the satellite signal received from the antenna mounted on the rooftop of the bus, against the Configuration Data. If the actual readings match those in the Configuration Data, the fare stage will be adjusted accordingly.

As the GPS signal serves as a secondary means of confirming the fare stage, VLS is able to allow accurate fare stage updating even if the bus does not stop at every bus stop.

VLS tracks the location of the bus, which in turn determines its fare stage. This means bus drivers need no longer update fare stages manually. It eliminates human error, thereby reducing the chances of charging commuters the wrong fare.

VLS will ensure accurate fare deduction. Commuters will still need to tap their ez-link Cards when they are alighting to ensure the correct fares are deducted.

.No, the VLS is unlikely to affect the operations of the ez-link Card system. On the other hand, it is the introduction of the ez-link Card system that has allowed us to develop the VLS to ensure correct deduction of fares. This was not possible in the past without the ez-link Card system.

However, some commuters may take some time to adjust to tapping their cards for exit only when they are near the bus stop they intend to alight at. We have tried to mitigate this by activating all the readers, both at the entrance and exit doors, a good 100 metres before the next bus stop. This should give commuters ample time to tap their cards.

For entry processing, we do not foresee any problems as the majority of commuters tap their ez-link Cards while the bus is at the bus stop, so they are unlikely to be affected by these changes.

VLS is a complex system that affects the entire bus operation. LTA and the operators have to conduct extensive tests on individual bus routes and buses to ensure the system is robust and reliable before implementation.

The first trial started as early as June 2003. Over four weeks, 200 students tried out the system on buses along 17 service routes. Another round of testing involving 35 service routes was carried out in April this year. Results from both tests have enabled us to fine-tune the system and verify the Configuration Data, such as route distances and bus stop co-ordinates.

We have conducted comprehensive tests on the VLS to ensure that the system is robust and reliable before implementation.

In the event that there is a failure with the VLS or GPS, bus drivers will manually update the fare stages. Bus operations will not be affected and commuters can tap their ez-link Cards as usual.

There will be stickers placed at the exit doors of buses to inform commuters of the changes to the operation of the card readers. Posters will also be put up at the bus interchanges to familiarise commuters with these changes.

Commuters who wish to tap their cards in advance to exit process can continue to do so with the implementation of VLS. There is ample time for them to do so as all readers are programmed to allow processing 100 metres before reaching the next bus stop.

Commuters may also continue to entry or exit process at the front readers, and exit process at the readers at the exit doors while the bus is at the bus stop.

Commuters can start tapping their cards after the "Reader Disabled" logo on the readers goes off 100 metres before the next bus stop. Alternatively, they can tap their cards after the bus stops at the bus stop and before they alight from the bus. The latter is already the most common method used by commuters today. There will be no change to this even after the launch of the VLS.

We will roll out VLS on nine service routes this Sunday, 1 August 2004. They involve a total of 88 buses.

41 buses are from SMRT Buses. They ply service numbers 173, 180, 184 and 189. The remaining 47 buses are from SBS Transit. The buses ply service numbers 40, 228, 265, 268 and 506.

LTA and the bus operators have decided to roll out VLS in phases to better manage the implementation process. This is a cautious approach which will allow us to monitor the performance of VLS in actual operations before rolling it out on more buses.

Commuters will not experience much change, except that the ez-link Card readers will be de-activated until the fare stage gets updated 100 metres before the bus calls at the bus stop. Hence, we do not expect or foresee any major problems with the implementation of VLS.