The Gant ruling is really quite simple and elegant if looked at by the issues in the case directly.
Gant was arrested OUTSIDE of his locked vehicle. That takes Seaches Incident To Arrest (SITA) and solidifies the line of when a LEO can conduct a vehicle search without a warrant and when they can't.
The LEO safety aspect of the ruling states that the warrantless search can only be conducted if the suspect still has reasonable access to interior of vehicle where any weapon could be found or evidence of suspected crime could be destroyed. Since Gant was already cuffed and sitting in the back of patrol car, he had no access to interior of car.
Another civil protection this case provides is as follows,
If LEO stops driver for speeding, runs license, and finds it suspended so he arrests driver...in the past, said LEO would now search arrested persons car to fish for any other evidence of crimes. After the ruling, said LEO cannot search vehicle after arresting driver on suspended license because, per the ruling, no evidence to solidify case against suspended license would/could EVER be found in car, so no fishing expedition by warrantless search is possible and if warrantless search is conducted, then any evidence found is inadmissable against any additional crimes charged with.