ERP explained: how Singapore prices a road by the half hour

Singapore introduced the world’s first urban congestion charge in 1975. The Area Licensing Scheme required a paper licence, displayed on the windscreen, to enter the central district during restricted hours, and it was enforced by people standing at the boundary looking at windscreens.

Electronic Road Pricing, launched in 1998, is that idea with the friction taken out.

What the charge is for

A gantry charges a vehicle for passing under it during a charged period. The rate depends on three things: which gantry, what class of vehicle, and which half-hour slot. The same gantry can charge nothing at ten in the morning and a substantial amount at half past eight.

That last point is the whole design. The charge is not for the road. It is for using the road at a moment when too many other people want to. Shifting a journey by twenty minutes can change what it costs, which is the behaviour the scheme is trying to buy.

Rates follow measured speeds

Rates are not fixed by statute and are not set to raise a particular sum. The authority measures average traffic speeds on the charged stretches and reviews the rates against a target band: fast enough that the road is working, slow enough that it is not empty capacity. Where speeds sit inside the band, the rate is left alone. Where they fall below it, the rate goes up; where they run above it, the rate can be reduced or removed.

This is why an ERP rate table is a poor guide to anything except the month it was published, and why a page like this one does not reproduce it.

The gantries are going

The successor system moves the charge off the roadside and into the vehicle. An on-board unit uses satellite positioning to determine where the vehicle is, and charges are applied without a structure overhead. Installation began in the mid-2020s and rolls across the vehicle population rather than switching over on a single date.

The significant part is what it removes: the need for a physical gantry at every charging point. A point-based charge requires somewhere to put the point. A system that knows where the vehicle is does not, which is what makes distance-based or cordon-based charging technically available.

Whether any of that is adopted is a policy question and has not followed automatically from the technology. The system was introduced to do what the gantries did, without the gantries.

How it sits next to the quota

The two schemes work on different things and are frequently conflated. The Certificate of Entitlement controls how many vehicles exist. Road pricing controls when and where those vehicles are driven. A country could run either without the other; Singapore runs both, and the vehicle quota premiums charted on the transport board are the price of the first, not the second.

For current rates, gantry locations and the state of the replacement programme, the authority is the source of record.