Reader Hor Chong Hann wrote in to askST: "What is the rationale for the Land Transport Authority (LTA) implementing Electronic Road Pricing on Saturdays for the Central Business District area?"

Transport reporter Zhaki Abdullah gets the answers from the LTA.

With a network of more than 70 active gantries islandwide, the Electronic Road Pricing (ERP) system is meant to manage congestion on heavily used roads, such as in the Central Business District (CBD) and Orchard Road areas, as well as on major expressways.

Though ERP gantries are currently not activated in the CBD on Saturdays, they are activated in other places like the Orchard Road area on that day. This is because the area is primarily a commercial district where traffic demand is high even after office hours, said the LTA, noting that severely congested roads would affect the business of restaurants and shops in the area.

"It is therefore necessary to implement ERP in the Orchard cordon up to 8pm during weekdays and Saturdays to maintain the flow of traffic," said the LTA, adding that the ERP helps keep traffic in the area moving at the "optimal range" of between 20kmh and 30kmh.

ERP rates vary for different roads and time slots, depending on traffic conditions in the area. This is to encourage motorists to change their route, mode of transport, or time of travel. For example, on weekdays for the Orchard Road gantry, the ERP charge between noon and 5.30pm is 50 cents, whereas on Saturdays it costs 50 cents between 12.30pm and 12.35pm, and $1 from 12.35pm to 6.30pm.

The LTA noted that for those who wish to avoid paying ERP charges, the Orchard Road area is served by several MRT lines and stations, as well as bus services.

Singapore became the first city in the world to have an electronic road toll system when the ERP was introduced in 1998, replacing the Area Licensing and Road Pricing schemes.