What speed mode is set by these signs on the road?

Explanation

These signs set a minimum speed of 50 km/h for the left lane only.

Here a compulsory speed floor is combined with a plate that limits its scope to one traffic lane. The result: in the left lane you must not travel more slowly than 50 km/h, but the other lanes of the same road are free of this requirement, and anyone who cannot or does not wish to hold that speed belongs in the right-hand lane. The technical reason is speed difference, not absolute speed: a slow vehicle in a fast lane creates a queue behind it and forces lane changes, and a large share of rear-end collisions and risky overtakes are born of that speed difference. A minimum speed closes that difference and keeps the left lane for an even flow. Memorise the figure 50 together with the qualifier "left lane only"; dropping the qualifier makes the answer wrong.

A minimum speed is not the same as a recommended speed: failing to hold the compulsory floor in that lane is an offence, not a personal choice.

• The plate beneath the sign has limited the scope to one lane; extending the minimum speed to the full width of the road would drive slow vehicles out of the right-hand lanes as well. • A recommendation is not binding, whereas this sign sets a compulsory lower limit and travelling more slowly in the left lane is an offence.

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