To be an accident-free city is Hong Kong's ultimate goal. Drivers, passengers and pedestrians all have a role to play in reaching this target, as do bridge and road barriers - the last line of defence in protecting road users.

On July 10 last year, 21 people died and 20 others were injured after a container truck hit a double-decker bus, causing it to crash through a guardrail and down a hill off Tuen Mun Road near Ting Kau Village. (See Full Story.) Since then, the Government has accelerated measures aimed at strengthening key barriers.

Better protection: Highways Department Chief Engineer Wong Po-chi explains the design of the new three-rail vehicular barrier. To strengthen protection for road users, a three-beam barrier has been installed in front of the existing parapet along Tuen Mun Road.

Highways Department Chief Engineer Wong Po-chi says engineers produced a preliminary design to improve existing barriers immediately following the incident.

Computer simulation tests found the new design's containment capability is double that of the existing design.

In an interview with news.gov.hk, Mr Wong explained the new design adds posts and rails to the existing vehicular barriers, known as P1.

"With this design, we can at least contain a bus at a speed of 65 kilometres per hour (kph) or above. This is a drastic increase to the original P1 barrier design, which can only contain a bus at 38kph," Mr Wong said.

"We are still doing enhancement on this design to see if further improvements can be made. But the design will only be confirmed and developed when we have a detailed one near the end of the year."

$13.6m barrier-strengthening works completed

Meanwhile, strengthening works have been done at 23 road sections, mainly along Tuen Mun Road and Tolo Highway, at a cost of $13.6 million. Additional three-beam barriers have been installed in front of the existing vehicular parapets.

Mr Wong said parapets of the same design were in use in some European countries. An additional metal beam offers a more flexible barrier and better protection to smaller vehicles, and provides interim enhancement to the barriers' containment capacity.

He said that lawmakers had approved a sum of $93.7 million in June to enable improvements to 39 priority locations that are similar to the spot where the Tuen Mun incident occurred.

The fund will be used to study ways to enhance parapets' containment capabilities and for upgrading existing parapets at the 39 locations.

These locations have in common a high posted speed limit, high traffic volume, and high bus and commercial vehicle usage. They are all close to an expressway entrance with weaving traffic, situated high above ground, with residents underneath the road sections.

Improvements to priority locations to start next month

"We will be doing the work in two phases to speed up the project. The first phase will be along the most critical parts, which are mainly along Tuen Mun Road. The works will commence in August, scheduled for completion in December," Mr Wong said.

"For the remaining locations, we will invite tenders in August or September this year with a view to starting the works immediately after the completion of phase one in December, that is, in January for completion in December next year."

P1 is the most commonly used vehicular barrier in Hong Kong, with a lifetime of about 10 to 15 years.

In 2000, the department enhanced the design of the three-rail P1 parapet. With strengthened post-to-rail and post-to-base connections, bolted splicing between rails, and re-oriented top rails, the enhanced design has better containment capability than the first generation.

More than two-thirds of P1 vehicular barriers upgraded

"We have been replacing the P1 parapet with this new design. After the incident, there is a need to speed up the replacement programme and now we have already replaced 70% of the 100-km P1 parapets," Mr Wong said. 

The other 30km will be replaced by December. 

Apart from improvement works, the department has also reviewed existing vehicular parapet design standards.

"We have adopted immediately in consultation with the Independent Expert Panel an interim standard for the containment of heavy vehicles and buses for selected locations. In future when more new roads and bridges are coming in, they will be treated similarly if they satisfy the criteria," Mr Wong said.

Academics to partake in design standard review

While the department's Structures Design Manual for Highways & Railways is in line with international standards, a comprehensive review will start in August in view of changes in the local scene.

"The underlying principle is to design parapets which can contain the majority of vehicles that cause traffic accidents. Hong Kong is no different than other places in the world. Light vehicles are the major accident vehicles which are involved in more than 80% or even 90% of the accidents. So in our design of different parapets, our target is to contain light vehicles traveling a little faster than the posted limit," Mr Wong said.

"However, the number of heavy vehicles in Hong Kong has been rising rapidly. There is a need to shift the balance point more to heavy vehicles. In the long run we want to have a complete review of this design manual to see what could be done and what could be enhanced."

The department intends to collaborate with universities to review the design manual and come up with ideas on whether the existing containment levels are adequate, and whether enhancements or the introduction of more containment levels are needed.

Study to explore use of multiple containment barriers

The study will also look into a multiple containment parapet design recently developed by some European countries.

The design aims to hold heavy vehicles without causing too much damage to light vehicles. The two-line parapet design has a barrier in front to protect light vehicles and one at the back to contain heavy vehicles. Its effectiveness is still being tested.

"In Europe, this is just a very initial idea. They have some trial installations at selected locations, not yet widely installed. The main concern is this type of parapet takes up quite a lot of space," Mr Wong said.

The study will begin in August, with recommendations to follow in six to eight months' time. Revised or new designs will then be worked out and detailed guidelines will be set for engineers to select the appropriate parapets for use at different locations.

"If the programme can be realised, we hope we can complete this study and the design work by December next year," he added.