ROAD congestion has been a talking point in recent years, with the passenger car population growing by 7.4 per cent in 2006 and a record 9 per cent last year.

To curb car sales and car usage, the Government recently announced an expansion of the Electronic Road Pricing network. It will also halve the allowable annual vehicle growth rate to 1.5 per cent from next year.

The aim is to get more car owners off the road and onto buses and trains. A sound objective on the whole, but congestion is surely too multi-layered a problem to pin the blame entirely on cars.

There are more than 500,000 passenger cars in Singapore, making up 60 per cent of the total vehicle population of 851,000. One could argue they are the main contributors to congestion.

Let us assume that is true. The assumption would lend logic to the punitive way private cars are taxed, making them among the costliest in the world.

But there are a further 150,000 or so vehicles which are also used for private transport. Most of these are taxed nowhere as heavily as cars. And we are not talking about motorcycles.

We are talking instead of commercial vehicles - vans, pick-ups, trucks, buses, lorries and trailers. They are meant for business use, and so taxed quite lightly.

Most of them are not subject to the 20 per cent Customs Excise duty that car owners pay. Most pay only 5 per cent in Additional Registration Fee (ARF), versus 110 per cent for cars. The bulk of these run on diesel, which is not taxed. Petrol duty is around 40 cents a litre.

The low taxes for commercial vehicles are meant to keep business costs down. But this goodwill has been abused for years. It is easy to spot vans, trucks, lorries and even trailer cabs being used as de facto cars. Granted, these are often low-income people who cannot afford taxis.

But there are also those who are quite well-off who buy commercial vehicles for private use. They can be spotted in Japanese mini-vans, diesel-powered Land Rover Defenders and even tow trucks - all bearing commercial vehicle plates.

In 2002, the Land Transport Authority clamped down on such misuse, requiring buyers to show proof that they own businesses. Even so, it has not stopped people from registering $2 companies to bypass the law. It is only now, with the arrival of China-made cars and the relatively low COE prices, that such vehicles are losing their shine among car buyers.

So what do we do about the 150,000 commercial vehicles which are sometimes used as de facto cars? In some countries, the authorities hold ad hoc checks on commercial vehicle drivers. If they cannot show proof that they are using the vehicle for work, they can be fined.

That is going to be difficult to implement here. The simplest solution would be to tax all vehicles alike. A panel van takes up the same road space as a Toyota Corolla, so they should be taxed equally.

This does not necessarily mean raising the commercial vehicle ARF to match the car's. Instead, the car ARF could be lowered a little.

In fact, it would be good if all the various vehicle taxes (except for motorcycles) could be made uniform. Removing the excise duty and having an ARF of 50 per cent would be a good start.

To minimise the impact such a move would have on tax revenue, the scrap rebate - which car owners get if they deregister their cars before the 10th year - should be, well, scrapped.

The simplification would free up the sizeable human resources the LTA and Customs department tie up to implement the various tax and rebate schemes.

More importantly, it would all but eradicate the problem of car importers under-declaring the value of their vehicles to evade tax. If ARF was low enough, there would be little incentive to cheat.

This would free resources and time spent cracking down on cheats - including the scams arising from the multi-million-dollar paper trade of scrap rebates.

A non-discriminatory vehicle taxation system is the way to go, especially when we already have in place as absolute a vehicle population control mechanism as the COE.

When asked recently why public buses were not exempt from ERP, Transport Ministry permanent secretary Choi Shing Kwok said the Government wanted to keep the system 'pure'. Hence any vehicle that contributes to congestion (except emergency vehicles) should be charged.

The application of upfront taxes should likewise be 'pure'.