SINGAPORE - The way motorists are charged will not change when the satellite Electronic Road Pricing (ERP) system kicks in, as the current model has been effective, said Transport Minister Ong Ye Kung.

In a Facebook post on Thursday (Sept 10), Mr Ong said it is much better to continue congestion pricing in a way that motorists are used to when Singapore switches to the new ERP system in 2023.

"Distance-based charging is a significant policy change which has many implications and should be studied carefully," he said.

Currently, motorists are subjected to a cordon-based congestion pricing framework where they are charged a one-off fee at gantries leading into more congested areas. A distance-based system, where fees would vary depending on how far motorists choose to drive, have had mixed reactions from the public.

Some think it is more equitable while others dread its implementation.

The new ERP system is capable of charging by distance, said Mr Ong, "but as a policy, we are holding back".

During the Budget earlier this year, Deputy Prime Minister Heng Swee Keat said the technology for distance-based charging was "still several years away".

In his post on Thursday, Mr Ong addressed questions and grouses from motorists about the new on-board unit (OBU) that will be installed in vehicles for free from the second half of 2021.

The three-piece OBU for vehicles comprises an antenna, a touchscreen display and a processing unit. It has drawn criticism for its perceived bulkiness.

Some asked why the three-piece unit could not be integrated into one, as with the OBUs issued to motorcyclists. Others asked if they could simply use their own phones instead and do away with the standard-issued units altogether.

Mr Ong said: "Technically there is no problem having an integrated unit. The issue is heat. From time to time, we park our cars under the hot sun, and a processing unit on the dashboard could not function without a big cooling unit."

Hence, the contractor designed it to be a separate module under the dashboard, instead of making it part of a much larger integrated OBU, he added.

The minister noted that the Land Transport Authority (LTA) may use the OBUs to alert motorists of other important traffic-related information when there is a need to, a function that would be more difficult if motorists just use their phones.

Using smartphones to pay ERP remains a "possible future upgrade", he added.

"But to start the new system, better to have a standard issue. If we use our own smartphones for ERP, there will be operational issues like battery running out, forgetting to bring smartphones, et cetera."

Data security was also a concern for the LTA in its decision to kickstart the new ERP system with the OBUs instead of smartphones, he said.

On concerns that the OBUs could block the windscreen and affect driving, Mr Ong said the dimensions of the new OBUs are only slightly bigger than the current in-vehicle units - 152mm by 80mm compared to 121mm by 78mm.

The LTA, together with workshops, will evaluate how best to install the units to minimise blockage of the windscreen, he added.

On comments about the lack of consultation on the OBU design, Mr Ong said the LTA had some practical constraints, having called an international tender for the project.

It had to choose the best system among the various proposals it received. Thereafter, it is contractually bound.

"There can be consultations and change of design but it will affect the contract," he said. "We will have to see how to do this better next time."