Bridging the John St gap
BRIDGING the financial gap may be harder to achieve than an engineering solution for the oft-debated John Street railway bridge, adjacent to the John Street, Mount Pleasant Road intersection.
Replacing the timber bridge and improving vehicle access under it, including allowing for the high vehicles which have sometimes come to grief against the existing structure, is turning out to be nowhere near as simple as it may sound.
Gympie Regional Council's Works and Services Committee last week recommended postponing a decision until a detailed report is available on the four options which seem to be available for upgrading vehicle access under the bridge and through the intersection.
The cost will be, according to information presented to the committee, “in the small millions” (of dollars) for a replacement bridge, not counting installation and the traffic signals which are planned but not yet installed at the intersection.
Apart from the simplest solution, which is to close the intersection altogether and forget the problems of low and narrow access under the bridge, the four options currently on the table are to install a new steel bridge, install one of two types of prestressed concrete slabs under the bridge or install a precast concrete bridge.
Council Engineering Director Bob Fredman told the meeting the “original thought was to get a heritage bridge with a longer span but it may not be that easy.”
He said traffic flows would also be an important consideration affecting the final choice, as well as cost.
A report to the meeting said that sourcing a second hand bridge had been considered, “with Queensland Rail contacted concerning the possibility of acquiring bridges on the Theebine-Kingaroy line.”
Queensland Rail said they might be able to help but only after a decision is made by the State Government about closing the line and planning the future use of the corridor.”
Alternatively, Queensland Rail has suggested that they have a number of steel bridge spans held in inventory but a suitable configuration had yet to be sourced.
Staff at this stage had tended to regard as “not preferred” the steel truss design option, “from an ongoing maintenance and safety perspective.”
However, the report said that the relative costs of each option had yet to be calculated.
One of the main concerns with the various options has been the need to minimise raising of the railway line, regarded as “a disruptive, time consuming and expensive proposition.
“Hence efforts have focussed on quantifying and minimising the raising required.”
The report said Option Four, with a structural thickness of 600mm, would provide a clearance of 3.6m. The project brief required a minimum clearance of 4m and a 10m clear internal span over John Street, with the difference to be achieved by raising the rail or lowering the road underneath.