Which vehicle driver has the right of way when changing lanes at the same time?

Explanation

The passenger car.

In the picture the truck in the left lane, indicating right, and the passenger car in the right lane, indicating left, intend to change lanes at the same time. For exactly this case there is a simple rule with no exceptions: when two vehicles travelling in the same direction change lanes simultaneously, priority belongs to the one on the right. Here the passenger car is to the right of the truck, so it has priority and the truck driver must wait.

Why is the law written this way? Because in a simultaneous lane change the two drivers enter each other's blind spots as mirror images, and without a clear criterion both steer at the same instant and collide precisely between the two lanes. "The right has priority" is a geometric, instant and unambiguous test — unlike criteria such as "who signalled first", which is neither observable nor provable.

The common trap is to think the heavier or larger vehicle has priority, or that because the truck takes longer to stop it should go first. Size and weight play no part in this rule. The sentence to memorise: in a simultaneous lane change, give way to the vehicle on your right. And on a real road, check your mirror and your blind spot separately before every lane change; the indicator announces intent, it does not obtain permission.

• The truck is on the left, and in a simultaneous lane change the left must give way. This option is tempting because you unconsciously equate size and weight with priority; the law looks only at lateral position.

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