Greek National Road 91 (Greek: Εθνική Οδός 91, abbreviated as EO91) is a highway in Attica, Greece. It runs from the centre of Athens to Sounio, via Vouliagmeni. It was first constructed in the 1950s as a one lane per direction road, but the section between Athens and Vouliagmeni was later[when?] extended to two lanes per direction. It has many extremely dangerous curves, and accidents happen on an almost daily basis. Currently, there are no plans to replace it with a bypass or reconstruct certain dangerous parts, but there has been an effort to increase police presence to prevent illegal racing and violation of speed limits which were common phenomena over the last 10 years. The highway becomes busier during the summer, as most of the places it connects are popular vacation spots.
The Greek National Road 91 begins in the centre of Athens, and runs southwest to the Saronic Gulf coast at Palaio Faliro. This section is named Andrea Syngrou Avenue. From Palaio Faliro it continues southeast along the coast, passing along the southern and southeastern suburbs of Athens. The section between Palaio Faliro and Glyfada is named Poseidonos Avenue.
The Greek National Road 91 passes through the following places: