Tonkin Highway

Tonkin Highway is an 81-kilometre-long (50 mi) north–south highway and partial freeway in Perth, Western Australia, linking Perth Airport and Kewdale with the city's north-eastern and south-eastern suburbs. As of April 2020, the northern terminus is at the interchange with Brand Highway and Great Northern Highway in Muchea, and the southern terminus is at Thomas Road in Oakford. It forms the entire length of State Route 4, and connects to several major roads. Besides Brand Highway and Great Northern Highway, it also connects to Reid Highway, Great Eastern Highway, Leach Highway, Roe Highway, and Albany Highway.

Planning for the route began in the 1950s, but the first segment between Wattle Grove and Cloverdale was not opened until 1980. Over the next five years, the highway was extended north to Great Eastern Highway and south to Albany Highway, and a discontinuous section was constructed north of the Swan River. In 1988 the Redcliffe Bridge linked these sections, and three years later, Reid Highway became the northern terminus. The next major works on the highway, between 2003 and 2005, extended the highway south to Thomas Road.

The central section of Tonkin Highway was upgraded to a six-lane freeway-standard road between 2013 and 2015, as part of the Gateway WA project to improve the wider road network around Perth Airport. From 2016 to 2020, construction commenced to upgrade the section of Tonkin Highway between Guildford Road and the original Reid Highway terminus to a six-lane freeway-standard road, and to build a four-lane freeway standard road up to Muchea, as part of the NorthLink WA project. The extension was originally known as the Perth Darwin National Highway. Planning provisions have been made for Tonkin Highway to be extended south of Byford in the future.

Tonkin Highway forms the entire length of State Route 4. It is a dual carriageway road maintained by Main Roads Western Australia, and subject to control of access along its entire length. Some junctions on the highway are at-grade and traffic light controlled; however, all junctions north of Hale Road in Wattle Grove and junctions with Albany Highway and Corfield Street in Gosnells, are freeway-standard with grade-separated interchanges. The central section of the highway between Reid Highway and Roe Highway is primarily six lanes wide; the remainder of the highway is primarily four lanes wide. The speed limit is 80 kilometres per hour (50 mph) near at-grade intersections, and 100 km/h (60 mph) along the stretches in between with 110 km/h (70 mph) north of Ellenbrook. A shared pedestrian and bicycle path is built alongside most of Tonkin Highway; namely between Muchea and Hale Road, as well as south of Mills Road East. In most other sections, the highway's sealed shoulders also function as bicycle lanes.

Main Roads Western Australia monitors traffic volume across the state's road network, including several locations along Tonkin Highway. The section near Perth Airport, south of Great Eastern Highway, is the busiest, averaging over 56,000 vehicles per weekday in 2007–08, and over 57,000 in 2008–09. North of the Swan River, the traffic volume gradually decreased to under 40,000 vehicles per weekday near the northern terminus, in 2007–08. Measurements in 2008–09 showed the lowest volume to be under 10,000 vehicles per weekday near the southern terminus, north of Thomas Road.

In 2013, immediately preceding the upgrade of Tonkin Highway's central section to a six-lane freeway-standard road, junctions in and around Kewdale, Forrestfield and Perth Airport carried traffic volumes beyond their capacity during peak periods. Average peak period traffic speeds in this part of Tonkin Highway were measured as 20 km/h (12 mph) or less in 2013. The slowest section was from Leach Highway to Horrie Miller Drive, which recorded an average of 14 km/h (9 mph) during the afternoon peak period. Traffic volume, exceeding 50,000 vehicles per day in 2012, is forecast to almost double by 2031. Traffic modelling showed that leaving the current network of traffic light controlled intersections in place would have resulted in gridlock by 2021. Following the completion of the Gateway WA project in 2015, the upgraded road network is forecast to have an average speed in peak periods of between 55 and 75 km/h (35 and 45 mph) in 2021.

Tonkin Highway commences at a roundabout interchange with Brand Highway and Great Northern Highway near the town of Muchea in the Shire of Chittering of the Wheatbelt region. The highway is a continuation of Great Northern Highway to/from the north of Western Australia with direction signage including Port Hedland some 1,550 km (960 mi) away. The interchange is characterised by both the installation of curvy green street lighting known as "wiggle poles" on both the bridge passing over the roundabout as well as on the westbound approach to the roundabout as well as a large road train assembly area to the southeast of the interchange.

After 1 km (0.62 mi), Tonkin Highway passes over the old Brand Highway connection between Muchea and Great Northern Highway (now known as Granary Drive) before curving to the southwest to pass over Muchea South Road and the Midland railway line. The highway then enters the Perth metropolitan region (the City of Swan LGA, or local government area) and provides a western bypass of the town of Bullsbrook. The highway curves back to the south to pass over a roundabout interchange with Neaves Road. After 5 km (3.1 mi), Tonkin Highway passes over another roundabout interchange with Stock Road West on the eastern side and Cooper Road on the west. A Heavy Vehicle Inspection Area is located immediately to the south.