Alternative route between Calga and Ourimbah

General Proposals for Improved Road Communication between Sydney and Newcastle


Taken from Main Roads, December 1960

The average daily traffic crossing Peat’s Ferry Bridge over the Hawkesbury River is now 6,600. Peak daily traffic on public holidays in the summer rises to 18,500 (24 hours). This traffic is carried on a two lane road (three lanes across the bridge) which, though reasonably well graded, has a ‘winding road’ type of alignment over many miles of rugged terrain. It passes through a number of villages and through the busy towns of Gosford, Wyong, Swansea and Belmont .

During recent years the Department of Main Roads has carried out extensive survey investigations in order to determine whether any route exists between Sydney and Newcastle superior to that followed by the existing road, as it is apparent that the traffic capacity of the main route between Sydney and Newcastle will need to be much greater than exists. The investigations have shown that, generally, a line close to the existing road is the most suitable available, with the exception that an alternate route departing a substantial distance from the existing route could be followed with advantage between Calga, (11.7 miles south of Gosford), and Ourimbah (7.4 miles north of Gosford); D-B-C on sketch plan.

On account of the volume of traffic, and its rate of growth, it was decided that the objective between Sydney and Newcastle should be a four-lane divided road having a high standard of alignment and grading and constructed as an expressway, that is, without frontage access and without cross traffic at road level.

The general scheme for the development of a Sydney-Newcastle expressway having being thus determined, detailed surveys were put in hand and plans prepared for the length which it was judged would give the speediest relief to traffic, namely between Calga and Ourimbah, which in the first place will serve as a bypass to the Gosford area. Subsequently detailed engineering surveys have been proceeding to the extent that staff can be made available on the defining of other lengths of the route. An origin and destination survey of traffic using the Pacific Highway indicates that when the new road si completed about half the traffic passing through Calga will use it.

The rate at which the Department can proceed with the development of the Sydney-Newcastle expressway proposals is limited by the finance available. In order to explore the possibility of securing the provision of a four-lane expressway earlier than would otherwise be possible, offers were invited recently for the construction and operation of a toll road to connect these cities.

While the route adopted between Calga and Ourimbah is slightly longer (1.1 miles) than the existing Highway between those points, it will provide both safer and faster travelling because of its much superior alignment and less local traffic.

The new route follows high country on a sandstone plateau up to 1,000 feet above sea level and skirts the deep valley of Mooney Mooney Creek. There are a number of citrus orchards, but much of the country is steep and undeveloped. Approaching Ourimbah the route descends from the plateau in a distance of about 2 miles.

A road existed along the adopted route north from Calga, and it was decided to improve this and use it, in the first place, as part of the new route, for a distance of 9.2 miles to a point 1.5 miles south of the village of Central Mangrove , rather than construct a parallel expressway at this stage. From Central Mangrove to Ourimbah, a distance of 11 miles, entirely new construction is required not utilising any existing roads, and it is on this length, which is being designed and built as a limited access road or expressway, that activity is at present concentrated.


Construction from Calga to near Central Mangrove

The road which existed between Calga and Central Mangrove was part of a Developmental Road constructed some years ago by Gosford Shire Council with funds provided by the Department of Main Roads. Work on its improvement to Highway standard for two lanes has now been completed. The formation was widened where necessary, minor deviations were constructed, improvements in grade effected and a bitumen surface provided.

Construction from near Central Mangrove to Ourimbah

This section of the route, 11 miles long, is entirely on new location. Only two lanes are being provided in the first place.

The new road will pass over existing roads at four locations (Nos. 1, 2, 4 and 5 on sketch) and under an existing road at one location (No. 3 on sketch). Traffic entering or leaving the expressway will be able to do so only at selected points known as ‘interchanges’.

Construction is in hand at present on the length between Central Mangrove and Somersby, where work is being carried out by the Department of Main Roads by day labour.

Design Standards

Between Calga and Central Mangrove the pavement is 22 feet wide flanked by gravel shoulders 6 feet wide. The improvements carried out on this section raised it to a 50 miles per hour design standard. The maximum grade is 8 per cent, for 1,100 feet, and the sharpest curves are one of 750 feet radius and one of 900 feet radius.

Between Central Mangrove and Ourimbah, the expressway ahs been designed for a speed of 60 miles per hour. The pavement will be 24 feet wide, and the shoulders up to 10 feet wide. The maximum grades are 6.4 per cent, and 6.5 per cent, for lengths of 2,600 feet and 3,800 feet respectively on the descent to Ourimbah. Elsewhere the maximum grade is 4.5 per cent. The minimum curves will be 1,000 feet on the descent to Ourimbah; elsewhere the minimum curve radius is 1,400 feet.

At Somersby an existing Main Road will cross over the new road on a reinforced concrete bridge 24 wide between curves and having a clearance of 17 feet 6 inches above the carriageway of the new road underneath. At four other locations mentioned earlier the new road will be carried over the existing roads on reinforced concrete bridges 41 feet between kerbs, providing for a pavement 24 feet wide with shoulders 8 feet 6 inches wide.


At the interchanges or points at which traffic may enter or leave the new road, entrance and exit ramps will be constructed. These will carry one-way traffic only, and will have pavements 14 feet wide and shoulders 6 feet wide. They will be so constructed as to suit the additional two-lane pavement of the expressway when it is ultimately built.

On the road as now being constructed there will be two interchanges between Central Mangrove and Ourimbah, one about 1.3 miles east of Central Mangrove, and a second at Somersby (Nos 1 and 3 on locality sketch). When the two additional lanes are constructed, there will also be an interchange near Central Mangrove and at Ourimbah.


Between Central Mangrove and Ourimbah, there are generally up to six feet of soil overlying sandstone rock except on the length of 1.5 miles in approach to Ourimbah where shales and mudstones are in places found below the soil. On the work in hand between Central Mangrove and Somersby, the overlying soil is being removed by tractors, scrapers and bulldozers. Where the sandstone is soft, it is broken up by a heavy tractor fitted with a single-tyne ripper. Generally, however, the sandstone is being broken up by blasting, using explosives in 3-inch diameter holes drilled by wagon drills at spaces of about 10 feet. A two-yard power shovel is used to load the sandstone into trucks for removal.

Compaction of fills which are being placed in thin layers is being carried out by the excavating equipment and by sheeps-foot rollers. Checks on the densities of the compacted matter are undertaken as the works proceed.


As the route of the new road throughout is over high ground and catchments are small, reinforced concrete pipe culverts generally suffice to carry water under the pavement excepting at one location where twin corrugated metal pipes 8 feet 9 inches in diameter have been used under high fill.

In cuttings, open drains 6 feet wide and 1 foot 6 inches deep, or mountain type concrete drains are being constructed where necessary.


He pavement between Calga and Central Mangrove was constructed in artificial gravel, composed of crushed basalt with the addition of 20 per cent, of laterite gravel. To reduce segregation and ensure uniformity in grading, ¾ inch, ½ inch and 3/8 inch and 3/16 inch to dust material was stockpiled separately, delivered and placed on the road in layers with a layer of laterite, each at pre-determined thicknesses, and then mixed with a pulvi-mixer and brought to optimum moisture before shaping and compacting. After compaction, a ¾ inch aggregate bitumen flush seal was applied to the pavement.

The provision of a pavement has not yet been commenced on the section between Central Mangrove and Somersby.

Acquisition of Land

In locating the route of the road between Central Mangrove and Ourimbah, special consideration was given to its effect on property, as well as to the suitability of the location. As the rad will ultimately be developed to a four-lane divided carriageway of expressway type, a wide reservation is necessary. Some of the land required is Crown land, but much of it is private property on which improvements such as orchards and farm buildings are located. Every effort was made to minimise the interference with properties especially orchards. Prior to commencement of the work, the Department’s proposals were discussed with the land-owners concerned, and negotiations were initiated for acquisition of land, provision of alternative access to severed areas, and adjustment of improvements, including dams.


The construction of the alternative route is being carried out under the supervision of the Department’s Divisional Engineer, Chatswood, Mr. H. C. Macready.

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