To meet growing demand for a greener cityscape the Highways Department is putting extra effort into its bridge design and construction to include more environmental elements.

Bridges & Structures Division Senior Engineer Chan Che-keung recently told news.gov.hk the department is studying the viability of planting grass on top of footbridges, and considering expanding the scale of vertical greening, such as under bridges and over noise enclosures.

Green scene: Senior Highways Engineer Chan Che-keung shows how plants will be added to the sides of a new footbridge on Lung Cheung Road. Examples of vertical greening can be seen on the Kong Sham Western Highway noise barriers and under the Canal Road Flyover.

People oriented

Mr Chan said the initiative will help them achieve their goal of "people-oriented development" to foster a quality living environment for residents, such as by installing covers and lifts for footbridges to give better pedestrian access.

Noise barriers will be built with transparent panels for greater visibility for the people, but with conspicuous stripes or eagle-like patterns to alert birds of their presence.

To reduce glare nuisance to nearby residents, the department will design noise enclosures with non-reflective glass roofs and study whether solar panels can be installed to power lighting and save energy.

Environmentally friendly

"New technologies in recent years have not only made quality upgrades possible, but also enable us to adopt more transparent designs allowing natural light and greening elements for bridges, giving a spacious and environmentally-friendly feel," he said.

To green the noise barriers, soil and fertilisers will be added to them for different plants, including flowers or climbers.

The department can place pot plants on bridge railings and sides. Greening is also possible under bridges, by choosing plants adaptable to a dimmer environment.

Main considerations

Mr Chan said before greening a bridge, consideration must be given to its design loading, and other issues including irrigation, drainage, impact on bridge maintenance and safety.

"The biggest constraint lies in the extra weight from soil and water, as the original design loading of existing bridges might not be able to cope with it. The bridge width is another constraint as we have to ensure pedestrian flow will not be affected after putting plants on it," Mr Chan said, adding newly-built bridges will be made wider. For example, a four-metre wide bridge will require a 25% increase in width for a 50cm extension on both sides to provide plant space.

As plants can rust bridge parts and affect inspections, one solution is to use rustproofing and to prune plants. Mr Chan said bridge safety is of prime importance and greening will be conducted as far as possible without compromising this.