Little people realize that the navigation technology in their car is much more modern than the ones in (modern) aircraft. Aircraft navigation is based on radar vectors and radio beacons, which lead to using "airways" to fly from one place to the other. Those airways are of course much longer than a direct route, leading to more fuel consumption, more time in the air, more CO2, etc.

For more than 10 years, the aviation industry is discussing using ADS-B as a replacement or add on for aircraft navigation. The difference is that the aircraft itself determines its position and broadcasts it to ground stations for use by Air Traffic Control. It promises direct routes, more aircraft in smaller airspace, and even better use of runways (more aircraft per hour). In this article (2007) it is explained that a runway can consume up to 1 aircraft every 45 seconds. 

The discussions are not over yet: In this article (written with a somewhat environmental bias and ditto non-scientific statements on aviation in general), as well as in the WIKI article the current state is well explained. It shows how fleet-durability, investment requirements and cooperation between multiple groups (airlines, air traffic control, governments etc) make these processes long and cumbersome.

The key for fast implementation is of course in the business case. You will not invest in something that won't bring benefits for years, or unless it is legally required. Perhaps someone should slice up the airspace  (in flight levels) for use by ADS-B equipped planes (with direct routes) and another space for those that are not. We'll see how much faster the adoption rates will be, especially in these time of high/rising fuel costs.