KEY POINTS:
About 14,500 vehicles a day are using a new $6 million bridge which has become the first structure to be opened on the $195 million motorway extension project through Mt Roskill.
The May Rd bridge is one of six crossings designed for the 4km extension of State Highway 20 between Hillsborough and New Windsor.
Its completion after a year's construction followed a delay of about two months while contractors dug out an embankment which was deemed unstable after most of the construction work on it was complete.
Test bores had not detected deep pockets of peat between basalt zones in the Mt Roskill lava field.
Ground had to be strengthened and lighter material used to fill up the embankment.
The bridge's two slender high-tech piers, each only 300mm thick but supporting its three spans between the northern and southern embankments, were unaffected because of the depth of the piles on which they are based.
Now that the bridge is open, earth-moving trucks will be able to move freely beneath it, speeding up ground preparation for the western end of the new motorway.
A diversion road used by local traffic over the past year while the bridge was being built is to be dismantled, although a vehicle ramp from the centre of the structure to the site of a proposed supermarket in May Rd has yet to be constructed.
Two combined cycling and pedestrian bridges over the future motorway are due to be completed early next year.
One is the $1.6 million link between Keith Hay Park and Mt Roskill Grammar and the other the $750,000 connection between Ernie Pinches St and Stoddard Rd.
Transit contractor Fulton Hogan is also preparing to start building a traffic bridge at Hayr Rd and motorway interchanges at Dominion Rd and Hillsborough Rd.
A section of Hillsborough Rd near its junction with the end of the Southwestern Motorway will be closed from December 27 to January 7, as will the motorway west of Queenstown Rd, to enable construction of a giant temporary roundabout to control traffic while the interchange is built in the middle.
