How did Greyhound come up with their 195? or their "1/3" less? Need to know to be able to compare or evaluate. And how full was the bus in their calculations?

BTW: _your_ calc of their calc is saying 2/3 less of Prius (they say 1/3 less). So this is all not very useful yet.

Try again?

The key is in the number of passengers.

Grayhound does not state how many passengers are on the bus. If the bus is presumed full then the above estimate could not go any lower. Instead it could go higher if the estimate above is based on a full bus and the bus is traveling at half capacity. In this scenario CO2 emissions per passenger double to 130 pounds.

However, if the Prius has 2 occupants the per passenger emissions are 98 pounds (195 / 2). If the Prius is comfortably full.... More

This analysis leaves out plenty, but perhaps the most important is the concept of "climate forcing." High altitude flight has a much greater impact than its carbon contribution might imply.