It runs north–south through the center of the city, from the coastal avenue by the Paraná River to the southern limit of the urbanized area (a total of 6.5 km).
San Martín St. starts near the river at Belgrano Avenue and climbs towards the downtown area.
The street returns to normal traffic four blocks later, at the intersection with Mendoza St. South of 27 de Febrero Boulevard, San Martín St. becomes a two-way avenue (26 m wide) that serves the traffic of a large area in the southeast of Rosario.
In this section there is a great number of stores, thus making it the commercial core of the southern neighbourhoods.
San Martín Ave. then meets Beltway Avenue and the municipal limit marked by the Saladillo Stream, and continues into the jurisdiction of the city of Villa Gobernador Gálvez.