Cars Only Roads


A solution to gridlock?

There is a solution to gridlocked road junctions, being built now here in Kuching, Sarawak, Malaysia which merits more attention from road designers and authorities. The fact that it is happening is one story. The question “why hasn’t this obvious idea been done before?” is another.

Surface Transportation News #147, has followed the progress of the scheme:

Innovative Underpass Project in Malaysia

Signalized intersections drastically reduce the throughput of major city roads arterials, compared with limited-access highways of the same number of lanes……………….

While the concept has not yet been implemented, an important step toward the idea is taking place in Sarawak, one of the states in Malaysia. The Borneo Post reported in mid-December that the Ministry of Infrastructure Development has signed a contract to implement a low-clearance underpass solution for the Petra Jaya Roundabout in Kuching. It’s intended as a pilot project for a projected 15 congested intersections in Kuching that had previously been planned for overpasses—but were not going forward because of both high cost and strong aesthetic objections.

The idea was first proposed to the Ministry in 2013 by Colin MacGillivray (a reader of this newsletter). The Ministry solicited an outside study from an engineering company, which made a persuasive case. The cost could be kept low by restricting the clearance height to 2.5 meters, allowing cars and light trucks up to 2 meters high—about 94% of all motor vehicles in the area. And by using underpasses instead of overpasses, aesthetic objections are almost entirely done away with. The 15 planned projects include some intersections with traffic signals and others with roundabouts. In both cases, higher vehicles will still be able to use the existing lanes.

MacGillivray notes that shallow underpasses have fewer, less-deep retaining walls, and shorter ramps compared with 5 meter full-height underpasses. And flyovers require 5 meter clearance underneath, which requires long ramps. They also must support the weight of all vehicles, including heavy trucks. Such bridge structures built from steel or concrete are expensive compared with roads on the ground, which is what underpasses are.

– See more at:

A submission to the Ministry of Infrastructure in July 2013 for upgrading a congested roundabout was approved by Cabinet in 2014. The validation of the concept was the existence of the A86 Paris Tunnel for cars only. The contract for the first pilot project at the Kipali Interchange also known as the Petra Jaya Roundabout started in November 2015.

The picture in the Borneo Post story shows the existing Petra Jaya 5 road roundabout with cars only underpasses serving the main directions of traffic flow.

The concept works at normal traffic light junctions as well. The cost of the work is 25% of the same routes using flyovers. At the Petra Jaya Junction 95% of vehicles can use the underpasses, so 5% use the existing route. Most urban roads, excluding industrial and port areas have over 90% or more cars. Even an SUV is less than 2 metres. Drivers are familiar with car parking buildings so underpasses are simple to use.

There appear to be no standards for “cars only” roads anywhere in the world.  JKR, the road authority in Malaysia are rightly being conservative.  The vertical and horizontal geometry for the first cars only roads, ramps and bridges as are as already specified for all vehicle roads which carry container trucks.

The essential point about this solution in any city is that as many junctions as possible should be upgraded to prevent down stream effects. That is why 15 upgrades have been identified by the Sarawak State Government

Here are some references about cars only roads:
Bob Poole has been actively promoting “cars only carriageways” for many years.
Academic paper from PANOS D.PREVEDOUROS, associate professor of civil engineering at the University of Hawaii at Manoa.

Paris A86 tunnel was built to avoid a historic area at minimum cost.

Cars Only Roads