I just came back from attending my cousin's wedding party in Semarang. It was 2.5 hours of driving from Semarang. Usually it took at minimum of 3 hours to reach Jogja, but thanks to the new highway, i can cut the travelling time to 30 minutes, just like before it gets crowded like today.
There will be more highware in the future, as the development of highway that connects Semarang and Solo are still in progress. If that's completed, we should be able to get there in shorter time.