Road sign S-1a: Dual carriageway

What it means

«Indica el principio de una autovía y, por tanto, el lugar a partir del cual se aplican las reglas especiales de circulación en este tipo de vía. […]» RD 465/2025, Annex I of the RGC (BOE-A-2025-12199), Spanish original.

The sign marks the start of a dual carriageway, from where the special rules for this type of road apply. It may also indicate the slip road of an interchange that leads to a dual carriageway.

Where you meet it

You see it at the start of the dual carriageway or on the slip road leading to it. Like the motorway sign, it is an information sign that switches on a whole legal regime. The series also includes S-1b, «Multi-lane road», and S-1c, «2+1 road».

What you must do

Apply the rules of the road from the sign. One exception: bicycles ridden by over-14s may use the shoulder of a dual carriageway, unless a sign bans it; not so on a motorway (RGC arts. 125, 38.1 and 36.2).

Details that count

The maximum on motorways and dual carriageways depends on category: 120 km/h cars and motorcycles; 100 buses, car-derived vehicles and adaptable mixed-use vehicles; 90 lorries, tractor units, vans, autocaravans over 3,500 kg, articulated vehicles and cars with a trailer (RGC art. 48.1.a.1). The minimum is 60 for everyone (RGC art. 49.1). S-2a marks the end of the dual carriageway.

What it is confused with

It is confused with S-1, «Motorway». Both have separated carriageways and no level crossings; what separates them is access from roadside land and that the motorway is reserved exclusively for motor vehicles (TRLSV Annex I, concepts 66 and 67). In the English exam an autovía is a dual carriageway, never a motorway.

Related signs

• S-1: Motorway
• S-3: Road reserved for motor vehicles
• S-5: Tunnel

Studied in topic 31: Motorways and dual carriageways.

Source: RGC arts. 36.2, 38.1, 48.1.a, 49.1, 125; TRLSV Annex I, concepts 66 and 67; RGC Annex I, sign S-1a (RD 465/2025).