What warning is given by a large white triangle painted on the road surface before a junction?

Explanation: Some junctions only have 'give way' lines. This is usually where there's relatively little traffic. 'Give way' signs, and/or road markings, show you that traffic on the road you want to enter has priority.

Category: Band 2 traffic signs and signals

References: Highway Code: Page 116, Know Your Traffic Signs: Page 69