Portugal's largest international air hub is the Aeroporto da Portela. This airport is about 4km northeast of the centre.
Many carriers operate scheduled international services to the Aeroporto da Portela. National carriers are TAP, Portugália and SATA.
Lisbon can be accessed from six main highways.
Coming from the south (A2) or east (A6 - the main route from Madrid), there are the two bridges:
Coming from the north, there is the A1, that connects Lisbon to Santarém, Fátima, Leiria, Coimbra, Aveiro, Oporto. The A1 ends near the airport. There's also the A8, which goes to Torres Vedras, Caldas da Rainha, Alcobaça, Leiria.
From the west, there is the A5, which connects to Estoril, Cascais, and the IC19 that crosses all the suburbs and ends near Sintra.
Lisbon has three ring roads: The 2ª circular, which connects the A1 to the IC19; the CRIL IC17 (still incomplete), which connects the Vasco da Gama bridge with the A1 and A8; and the CREL A9, which connects the A1 with the A8, IC19, A5, and goes all the way to the Estoril coast.
Regarding toll highways - Portugal has a unified electronic toll paying system - it's usually on the one or two left most lanes of the toll booths, marked with a green "V" (Via Verde - "Green Lane"). If you don't subscribe to the system, pay the toll at the manned booths (cash and most debit and credit cards accepted). If you by chance get distracted and go through the Via Verde lane, you have 48 hours to go to a Via Verde office and pay the toll without a fine.