The other pillar of Singapore’s traffic demand management strategy is road pricing. Road pricing serves as an effective tool to manage traffic congestion as it helps to internalise the external costs of driving e.g. the impact on other road users, so that motorists are more aware of the true costs of motoring.
Road pricing was first implemented in the form of the Area Licensing System in 1975, which levied a flat charge on all vehicles entering the Central Business District (CBD). In 1998, this was replaced by the Electronic Road Pricing (ERP) System, which leverages on technology to allow for a more effective and flexible method of congestion charging. The Radio Frequency Identification (RFID) technology used also allows an automatic deduction of congestion charge on any vehicle passing under a road pricing gantry during its operating hours. As charges are levied on a per-pass basis, motorists are more aware of the true cost of using their vehicles.
Purpose and Effectiveness
The ERP system provides a targeted solution for congestion pricing by allowing the authorities to pin-point specific congested spots and vary the congestion charge according to prevailing traffic conditions. Therefore, the charges can either increase or decrease according to the demand of usage of the priced-road or expressway, which is reviewed quarterly.
By pricing congested stretches, ERP system helps to moderate and spread out vehicle usage for optimal usage of the road network by encouraging motorists to consider alternatives. These would include using other routes to arrive at their destinations, travelling during the off-peak periods, switching to public transport or car-pooling.
Since its introduction, the ERP system has been effective in managing traffic congestion and resulted in traffic speeds remaining within the optimal speed range. However, the ERP system cannot operate in silo and has to work in tandem with vehicle ownership control measures, increasing and optimising road capacity, as well as encouraging motorists to shift to public transport to maintain a smooth-flowing road network.
Traffic Measurement Method
Since July 2008, LTA has gradually applied the 85th percentile speed measurement method to determine whether ERP rate changes are necessary, instead of average (mean) speeds, starting from the city centre to the rest of the gantries on the outskirts.
The current lower threshold speeds (45 km/h on expressways and 20 km/h on arterial roads), set 10 years ago based on an NTU study, are close to the point where traffic can easily slip into the unstable zone where ‘stop-start’ conditions become common. In order to create a buffer, LTA decided to use a more representative method of measuring actual traffic conditions for ERP rate reviews, with speeds determined using the 85th percentile method.
The 85th percentile speed method is an international traffic engineering practice for assessing traffic conditions. With the revised speed method, 85 per cent of motorists will experience speeds above the threshold.
ERP II
As congestion becomes increasingly pervasive, it would not be practical to continue erecting physical gantries to address the congestion problem. In addition, the ERP charges imposed at discrete gantry points also lead to undesirable consequences e.g. congestion spills over to nearby minor roads in residential areas, thus leading to localised congestion.
In the longer term, the LTA is looking into upgrading the ERP technology to put in place a more effective system of congestion management. It is envisaged that the next generation ERP system (ERP II) can help to overcome such problems by making distance-based congestion charging possible along congested stretches of roads and expressways.
This would be a more equitable and economically efficient system than the current point charging system where motorists are charged based on the number of gantries they drive through rather than distance travelled on a congested road. Furthermore, motorists who join a congested road after the gantry points are not charged even though they also contribute to the congestion of the road.