Electronic road pricing (ERP) rates in Singapore will go up to a new high of $4 per pass for car-owners from Monday.

The charge - the highest since the rates were introduced in 1998 - will hit drivers using the Pan-Island Expressway (PIE) slip road into Central Expressway (CTE) between 8.30 am and 9 am.

The revised ERP rates were greeted with dismay by motorists, especially cabbies, who are bracing for a sharp drop in the number of passengers taking the route.

According to The Straits Times today, the ERP will be raised by 50-cent for use of the Central Expressway (CTE), East Coast Parkway (ECP) and Pan-Island Expressway (PIE).

For car drivers using the PIE slip road into the CTE between 8.30 am and 9 am, the hike will take the charge up to $4. Drivers of heavy goods vehicles will hav eto pay $8.

Car drivers using the slip road between 7.30 am and 8.30 am pay S$3 - an increase from S$2.50 now.

Car drivers passing the CTE gantry north of Braddell Road towards the city will pay S$2 between 7.30 am and 9 am - up from S$1.50.

Those passing the ECP Fort Road gantry have to pay S$1.50 between 7.30 am and 8 am; S$2.50 between 8.30 am and 9 am and S$1 between 9 am and 9.30 am ? up from S$1, S$2 and Singapore fifty cents respectively.

Charges at all other gantry points will remain unchanged.

Reacting to news of the higher ERP rate, taxi driver S. H. Ngiam told The Straits Times: "I foresee 40 per cent of my customers will not take that route. They will bypass the route and cause bottlenecks elsewhere."

Transport researcher Paul Barter describes the S$4 charge as 'kind of alarming', but notes that ERP rates changed according to traffic patterns.

The assistant professor at the Lee Kuan Yew School of Public Policy predicts that the next generation of ERP may 'spread the charges around' to more roads to avoid sharp pricing at isolated gantries.

He also envisages distance-based charges requiring motorists to pay according to the length of the journey rather than the current flat rate.

One way to make this palatable, he says, is for ERP revenue to be used more directly to improve public transport in congested corridors.

The Land Transport Authority reviews ERP rates quarterly to 'achieve optimal traffic flow' - defined as speeds of 45kmh to 65 kmh for expressways, and 20 kmh to 30 kmh for main roads.

Rates for some gantries were reduced by Singapore 50 cents in the last review in November last year. The next review will be in May.

Meanwhile, off-peak hours cars characterised by their white-on-red number plates are getting red-hot in Singapore.

Record sales nearly doubled their number to 24,213 last year - nearly ten times the figure just three years ago.

The spike, said a Straits Times report, is due largely to the relatively lower prices of the cars, especially budget models, which are made even cheaper after the $17,000 tax-break for off-peak cars.

More than one in 20 cars on the roads here today is an off-peak car. It can be driven before 7 am and after 7 pm on weekdays, and any time on weekends and public holidays. Owners can use them outside the stipulated hours if they buy a $20 supplementary day licence.

Last year, 12,476 new off-peak cars were snapped up, a huge increase from 7,054 in 2005 - setting a new high for off-peak car sales for the fourth year running.

Most were budget cars, essentially because the $17,000 tax break works to be a a bigger percentage price cut on cheaper models.

First-time car buyer Teo Chai Soon, a minibus driver, bought an off-peak China-made Chery QQ in November for S$19,000, after subtracting the tax break.

The 40-year-old father of two young children says: "The car is cheap and something I can afford. My wife is a Malaysian, so a car is more convenient when we visit her folks."