The Interplanetary Transport Network is a kind of space highway that uses the gravitationally determined pathways to propel space craft from one body to the next. The fact that you use the gravity to propel from one body to the next means that you won’t use much energy/fuel but the journey would take a much longer time.
As of now these pathways aren’t meant to transport humans around the galaxy, they are used for probes that travel deep into space for observation.
The pathways were first found by Jules-Henri Poincaré in the 1890s. He noticed that the paths leading to and from any of these points would almost always settle, for a time, on the orbit around it.
Work by Edward Belbruno in 1994 provided the first insight into the nature of the Space Highway between the Earth and the Moon that was used by Japan’s first lunar probe. Beginning in 1997 Martin Lo, Shane D. Ross, and others wrote a series of papers identifying the mathematical basis and applying the technique to the Genesis solar wind sample return, along with Lunar and Jovian missions. They referred to an Interplanetary Superhighway (IPS).
This was the first lunar probe launched by a country other than the Soviet Union or the United States. Also of note the Hiten was the first to perform an aerobraking maneuver by a deep space probe. The probes mission concluded in 1991.
NASAs Genesis Mission used these space highway slow lanes to reach the Earth-Sun L1 point to study solar winds. Genesis was launched on August 8, 2001, and crash-landed in Utah on September 8, 2004, after a design flaw prevented the deployment of its drogue parachute. Genesis collected solar winds and brought them back to Earth. The Genesis science team demonstrated that some of the contamination could be removed or avoided, and that the solar wind could be analyzed using a variety of approaches.
Also, The International Cometary Explorer probe transited between the Sun and Halley’s Comet in March 1986, flew through the tail and its minimum distance to the comet nucleus was 28 million km. This probe continued on to 1997 along the space roads until it was deactivated. In 2008 a status check found that only 1 of 13 instruments have failed.