Is there a better option to the 'carro publico' (fixed-fee trans-city vans) for Puerto Rico commuter's needs?

Being an island PR should begin implementing the use of buses for medium-long distance range transportation.

A carro publico is great to take people from inside a town to the adjacent ones, but for longer distances it is a very poor option.

A better solution would be interstate-type buses as they are ideal for:
– reducing transportation cost
– reducing transit time
– expanding range of cities to go work/study at
– improving availability of public transportation (carro publicos currently do not operate on Sundays, and offer no service after 6pm aprox. the rest of the week)
– Improvement of quality of life as polution would be reduced. Ex. One Greyhound bus can take up to 54 cars off the road and achieves 258 passenger-mile per gallon of fuel.

Do you think there are other/better options vehicle-wise to help solve the current need?