DOZENS of bus routes and timetables across the Perth metropolitan area will be changed from February 1 when Year 7 students start high school for the first time.

Transport Minister Rita Saffioti said the new Purple CAT would add an extra 470,000km on to the bus network, taking in parts of West Perth, Subiaco, Shenton Park, Nedlands and Crawley.

Transperth’s free high-frequency CAT buses are paid for with a city-wide parking levy and are among the most successful and well-regarded bus services on Transperth's metro network.

Perth's new $8.2 million Green CAT service launches on Monday with the state government hoping each bus load of passengers will take 50 cars off the city's congested roads.