A smoother expressway experience for all with ramp metering

The Bus Service Enhancement Programme and recent enhancements to bus priority measures are valuable additions to our public bus system.

However, a missing link remains. Without concerted measures to ensure buses have a comparative advantage when entering and using expressways, express, long-haul and premium services will be limited in their impact in enhancing the convenience of commuters.

Buses should ideally have a dedicated lane on expressways, such as high-occupancy vehicle (HOV) lanes or bus rapid transit (BRT) services seen in other countries.

There is another widely-adopted measure that we could introduce here to create a win-win situation for both buses and private vehicles. Ramp metering is a measure used in many other regions, including Australia, East Asia, Europe and North America, to control the flow of slip road traffic entering expressways by allowing only one vehicle, or a limited number of vehicles, to pass at a single time.

This is accomplished by installing a traffic signal for each lane in the entering slip road that displays either a red (stop) or green (go) light. The lights alternate quickly to ensure only one vehicle from each lane passes at a time. The traffic signals are positioned right before the slip road merges into the expressway.

Studies have shown these ramp signals streamline the vehicular flow, maintaining regularity in both the main expressway flow and the entering slip road flow. This has been shown to increase vehicular throughput, speeds and safety. In addition, the merging traffic is less chaotic.

By programming ramp meters to give priority to buses and carpools, high-occupancy vehicles will have more streamlined access to expressways. Hence, buses will have priority when entering expressways, while vehicles will generally have a smoother expressway experience.

The implementation of ramp metering requires public education, increased enforcement, careful algorithm design on an islandwide scale and potential infrastructural enhancements to handle the suburban vehicular queue at high-traffic slip roads.

In addition, variable display signs are required to redirect traffic from entry points with heavy vehicular flow to alternative routes when necessary. When designed and implemented carefully, the benefits of this congestion-reducing scheme have been known to far outweigh the costs in other countries.

It is time that a paradigm shift from a private-oriented to public-oriented system be implemented in our transport network, in keeping up with the progress made by other cities in this area.