St Paul's Bay Bypass

We refer to the letter entitled Standards At St Paul's Bay Bypass by Andre Zammit (August 10). In this correspondence, a number of technical criticisms were levelled at the way in which the recently completed St Paul's Bay Bypass was planned and designed by the ADT. For the benefit of those readers who may have been misguided by some of the technical assertions made by the correspondent, we should like to set the record straight. We would also like to extend an invitation to Architect Zammit to discuss with our design and engineering team some of the technical issues in more detail.

Road geometry: The design speeds of the road have been planned and designed according to the geometry and radii of curvature required by the Design Specifications. The stretch between Erba Mwiezeb Roundabout (NA8) and the area known as "il-Ghollieq" (Chainage 1+600m ca.) caters for the national speed limit i.e. 80km/hr since the radii of curvature of this stretch are within the required limits for this speed. From this point till the Xemxija Roundabout (NA7), the radii of curvature imposed by the existing bridge structure and the existing residences permit a 50km/hr speed which is clearly marked on site. This speed limit is also required due to the residential zone and pelican crossing situated at Ta' Fjuri Area. Notwithstanding the above, part of this stretch has been temporarily downgraded to 40km/hr due to the current diversion which shall be removed when the bypass is entirely opened to traffic.

Open storm water culvert and safety fences: The installation of safety fences along parts of the St Paul's Bay Bypass is definitely not "an admission of failure". If this were the case, professional road designers world-wide would be hanging their heads in shame! The safety fences are installed as a standard safety feature on central strips to prevent the intrusion of vehicles crossing over into the opposing traffic stream. At the roadside, safety fences are commonly installed to both psychologically and physically deflect road users away from potential fixed hazards such as bridge abutments, steep embankments, trees or, in this case, the open storm water culvert, where this is situated in a bend and when there is a change in level between the road level and the fields behind the storm water culvert. The safety fences installed are of the un-tensioned corrugated beam type, which absorb the impact and direct vehicles back onto the carriageway and are according to the respective standard.

Asphalt structure adopted: The asphalt pavement adopted in the project consists of a 20cm asphalt structure according to the Road Works Regulations 2003 as follows:

4cm asphalt wearing course 0/12,5mm
6cm asphalt binder course 0/19,0mm
10cm asphalt base course 0/25,0mm

This structure in combination with the underlying unbound material (thickness according to the sub-grade) is designed to withstand a design traffic loading of three to 10 million equivalent 10-ton axle passes during its service life. The 48cm asphalt thickness mentioned covers a mere 250m stretch of one of the two carriageways forming this three kilometre road, in which for technical reasons it was decided to adopt such structure rather than opting for a deeper granular material structure which would have increased the risks of damaging the structures adjacent to this particular stretch road.

Wearing course: The wearing course adopted throughout the extents of the project consists of imported basalt aggregate (and bitumen) meeting all the requirements of the Road Work Regulations 2003 for such a layer and in which high resistance to abrasion and polishing is just one of the requirements stipulated.

Viewpoint: The intention of the viewpoint is to provide road users with a safe place where one can stop and appreciate the scenic beauty of St Paul's Islands and the surroundings without affecting traffic flow.

Just for correctness sake the bypass' opening was only delayed by a few weeks and not "several months".