A shuttle bus is usually a simple, small bus that takes you a short distance.  I do not know the translation in Portuguese.

     Let's say that you drive your car to the airport and park 3 km away.  How do you get from the parking lot to the airport terminal?  You take a shuttle bus.

     In a large airport (Bogota, for example) the distances between the gates can be quite big.  To from one gate to another you may have to take a shuttle bus.

     When you rent a car at an airport, how do you reach the parking lot of the rental company?  By shuttle bus.

    http://www.aeroportosdomundo.com/americadosul/brasil/aeroportos/galeao.php
Transporte Público
Ônibus, táxis e shuttles expressos transportam os passageiros até o centro da cidade. (Tempo de viagem: 30 a 40 minutos). Os autocarros partem de hora em hora desde o aeroporto para os principais hotéis e praias, e cada 30 minutos há um autocarro público que vai para o centro da cidade.

     To my mind in this sense can be called Expressos, ou ônibus Especiais Dale.  However, airport and tourim people are borrowing the "Shuttle" word these days.

    In the case of Rio, if one takes the 998 Charita/Galeão, they may reffer to it just as "Galeão" or "Galeão/Charitas", everybody knows that is a special line.

     Same to the bus line set in Xmas time, to serve prospective buyers of Niterói Shopping, the bus line is put in place, so people of distant neighbourhoods don´t have to take two or three buses to get to the mall. Anyway, the bus goes from a determined stop (point A) to the Mall, and then back in the reverse place, then saving time.

     Executive buses (ônibus executivos) are  in general, understood as buses with air conditioning and leather chairs.    In Rio there are some lines with such buses, some are "expressos" in the sense they have less stops and a special route, due to the air conditioning, people there nickname them "frescão/frescões".    Their fares are slightly more expensive