HOW much priority should the City of Cape Town give to public transport over private vehicles? Cape Town’s new Integrated Rapid Transit (IRT) system borrows many lessons from Bus Rapid Transit (BRT) systems in South American cities, where leaders have been prepared to limit radically the space available for private vehicles in order to build bus lanes. The assumption was that this would be balanced out as more people used public transport and left their cars at home.

The City of Cape Town has taken a more pragmatic approach, following the principle that the IRT infrastructure should have no lasting impact on the currently available road space, which is too busy as it is.

Instead, new lanes are being built in the road reserve, or entirely new roads are being built just for buses on available land. Where these options aren’t available, buses will be required to operate in normal mixed traffic, or share a single lane. So far the City has also avoided expropriating land to expand roadways.

But there are places where simple solutions cannot provide all the answers. One of these is at intersections.

In South America, many buses are equipped with wireless sensors that turn traffic lights green so they never have to stop. This can cause long delays for motorists trying to drive across the bus lane and so is not considered an option for Cape Town.

But at the same time, it would be impossible to run a scheduled bus service if buses get locked up for long periods of time at intersections.

Instead, Cape Town is preparing to introduce a hybrid system where buses that are running late will trigger a slight variation in the programming of the traffic lights ahead of them. This will help them get through a bit faster without giving them overall priority.

But the problems don’t end there. For intersections to function smoothly, they require additional lanes to separate vehicles that are going forward and vehicles that are turning.

This means that there often isn’t space for new bus lanes in the areas before and after intersections. And, where the bus lanes split at an intersection, buses may also require extra turning lanes.

In South American cities, one solution has been to ban vehicles from turning right at intersections along BRT routes, eliminating the need for turning lanes. However this requires rerouting traffic along surrounding roads, and is not really an option in residential areas.

Instead, engineers working on the IRT system have had to come up with customised solutions for sharing the road at each intersection.

An example of this is a ‘pre-signal system’, where traffic lights are set up just before an intersection’s turning lanes begin. These lights control the sharing of the turning lanes between buses and cars, and also allow buses to ‘jump the queue’ waiting at the intersection.

Changes like this require significant upgrades to the structure of intersections. The surfaces of intersections also have to be replaced to make the tarmac strong enough for buses to travel on regularly, as is the case on all parts of the road where buses will travel in the same space as cars.

When these upgrades are taking place, Capetonians can expect short-term disruptions in traffic going through intersections on IRT routes, but they can rest assured that in the long run, they are getting the best possible compromise, with the new IRT system set to ease traffic congestion significantly while causing minimal disruption to the existing road space.

Source: Cape Town