An ESTA travel authorisation is only related to "permission to travel to the United States", whether it be to visit or transit through to another destination. An approved ESTA travel authorisation does not guarantee entry or transit through the US. If you are planning to transit through or visit the US within the next six months, it is recommended that you begin the application process now. If you travel to the US and are denied entry, you will never be able to enter on the VWP again, and will in future be required to apply for a B-2 Tourist Visa.
Yes. A traveller planning to transit through the US en route to another country must also obtain an ESTA Travel Authorisation in advance. When he or she completes the ESTA application, the words "In Transit" and the final destination should be inserted into the address field under the heading "Address While In the United States".
Travellers transiting through the US under the VWP must also possess an ESTA travel authorisation. This requirement came into effect on January 12, 2009. If your application for an ESTA travel authorisation is denied, you must apply for a B-1 Visitor Visa or B-2 Tourist Visa. The visa application process can take weeks or months to complete.