Krusty land shuttle?
Do you mean change like this?
http://images2.wikia.nocookie.net/__cb20130716154305/simpsonstappedout/images/7/71/Shuttlebus.png
http://i0.wp.com/tstotips.com/wp-content/uploads/2013/08/C9L6Dtw.png
http://images4.wikia.nocookie.net/__cb20130829215816/simpsonstappedout/images/6/6f/UDc1KrK.png
If so, they're upgrades that happen as your Krust-O-Meter increases.
*sorry for the huge pics, too lazy to resize :p
http://images2.wikia.nocookie.net/__cb20130716154305/simpsonstappedout/images/7/71/Shuttlebus.png
http://i0.wp.com/tstotips.com/wp-content/uploads/2013/08/C9L6Dtw.png
http://images4.wikia.nocookie.net/__cb20130829215816/simpsonstappedout/images/6/6f/UDc1KrK.png
If so, they're upgrades that happen as your Krust-O-Meter increases.
*sorry for the huge pics, too lazy to resize :p
