you're about to merge into a lane without lane markings. who should give way to you?

On an unmarked merge where two lanes simply become one and there is no broken lane line between them, the vehicle that is ahead has priority, and the driver behind must give way and merge in behind.

Quick Scoop

• If there are no lane markings separating the two lines of traffic at the merge point (a classic “form one lane” or zipper-style merge), the rule is:
  • The vehicle in front has right of way.

* The vehicle that is slightly **behind** must slow down and give way, merging in behind the one ahead.

• If there were broken lane lines and your lane is ending, then you (the one changing lanes) must give way to traffic in the continuing lane—but your question specifically says “without lane markings,” so the “car in front” rule applies.

A simple way to picture it

Imagine both lanes narrowing into one funnel with no lines between them.
Whoever’s nose of the car is even slightly ahead keeps going, and the other driver tucks in behind. That’s the “zipper merge” idea: one car from each side, in turn, but always yielding to the one already in front.

Key tips for this situation

• Check mirrors and blind spots, then indicate before you merge.

• Don’t speed up just to “beat” the other car; forcing your way in can make you at fault if there’s a collision.

• If in doubt, err on the side of caution and give way rather than trying to claim “right of way.”

TL;DR: In a lane merge without lane markings , you give way to any vehicle that is ahead of you; the car in front does not have to give way to you.

Information gathered from public forums or data available on the internet and portrayed here.