Mr Ivan Tan Ri Yao has rightly pointed out that the recent increase in Electronic Road Pricing (ERP) rates on the north-bound Central Expressway (CTE) may reduce the ongoing snarl-up by pricing out motorists who are averse to paying the higher tolls ("ERP an effective way to ease congestion"; Forum Online, Aug 29).

The desired impact is highly case-specific though, and relies on several factors, such as the price of the toll to the affected road user, the availability of alternative routes and modes of public transport, as well as the preferences of drivers.

The question that the Land Transport Authority should ask is: Where do these road users go during peak hours to get to work?

The ERP is considered an effective mechanism in diverting traffic away from a congested stretch of road and regulating the growth in private transport, which contributes to a shift to more sustainable modes of public transport.

In reality, the implementation of ERP on certain roads merely shifts vehicles to non-priced roads, thereby having little effect on overall congestion.

Given the constant demand for driving, a price hike on the CTE may initially lead to reduced congestion.

However, when drivers discover that alternative routes are in a gridlock, the likelihood of them shifting back to the CTE is far greater than of them switching to public transport.

Road congestion will increase again - this time, perhaps with even more vehicles stuck in the queue, as previous users of non-priced routes now switch to using the CTE.

Edmund Khoo Kim Hock