Road sign P-17a: Carriageway narrows on the right

What it means

«Peligro por la proximidad de una zona de la vía en la que la calzada se estrecha por el lado de la derecha. […]» RD 465/2025, Annex I of the RGC (BOE-A-2025-12199), Spanish original.

The sign warns of an area where the carriageway narrows on the right-hand side. The official text adds a nuance: it can also be used when the right-hand shoulder is reduced, and it is not used if, after a lane is dropped on the right, the width of the remaining lanes and shoulders has not changed.

Where you meet it

It appears before the narrowing. In this series the letter says on which side width is lost: «a» is the right, «b» the left, and no letter means both.

What you must do

Moderate your speed: it is a triangle, so it imposes no numeric limit, but it does trigger the duty to moderate under article 46 (RGC arts. 144.1 and 46.1).

Details that count

Two details on warning signs. First, size: it follows speed, not the number of users, and is large on motorways and dual carriageways, intermediate on conventional roads with a shoulder and multi-lane roads, and small on conventional roads without a shoulder and in town (RGC Annex I, para. 5, volume II, 1). Second, on an illuminated sign the drawing is made with light and the background stays dark: it is the inversion of daytime contrast, not a change of meaning (RGC arts. 144.4 and 145.5).

What it is confused with

It is confused with the bend signs P-13 and P-14, because they use the same final letter with another meaning. On bends, the letter is the direction of the first bend, not of all of them. On P-17, the letter says on which side width is lost. Same «a» or «b», different question: read which family is in front of you.

Related signs

• P-13b: Dangerous bend to the left
• P-14b: Dangerous bends, the first to the left
• P-16b: Steep ascent

Studied in topic 10: Vertical road signs.

Source: RGC arts. 46.1, 144.1, 144.4, 145.5; RGC Annex I, para. 5, tomo II, 1; RGC Annex I, sign P-17a (RD 465/2025).