I agree to DaveReidUK, its worth to take a closer look on this systems.
Fuel saving is not the only advantage. Risk of FOD is decreased, reduced run-time of engines, brakes are preserved, …
But from my point of view Taxibot is a solution for smaller airports with less traffic, because somebody has to guide all the tugs on their way back.
The automated jetTRACS systems is a very interesting idea for larger airports, because the guidance system is integrated into airport and ATC systems. In addition jetTRACS follows an approach with a hybrid drive train without diesel engines. This adds an extra benefit.
I'm excited to see the first jetTRACS on an airport.