You are comfortable cruising at 40 in the right lane of a 65 mph freeway on a clear day with light traffic, and cars are stacking up behind you. What does the law say about driving so slowly that you disrupt the normal flow?

Why B is correct

Speed limits work in both directions: you may not exceed the maximum, and where a minimum applies — as it does on limited-access highways — you may not fall below it without cause such as weather, congestion or a mechanical problem. The logic is the crash research itself: collisions on high-speed roads correlate with speed differences, and a car moving at half the flow manufactures those differences continuously, along with an endless series of overtaking manoeuvres performed around it. Slow has to mean appropriately slow, not arbitrarily slow.

Why the other options are wrong

A. Drivers behind must wait; slower is always safer, whatever the posted minimum

'Slower is always safer' is exactly the intuition the crash data contradicts on high-speed roads. Below a certain point, further slowness stops adding safety and starts manufacturing conflicts for everyone negotiating around you.

C. Only trucks are required to maintain the normal flow

The obligation to keep with the flow applies to every vehicle on the roadway. Trucks are the most visible slow movers and the most regulated, but the minimum binds all traffic equally.

D. You may drive at any speed provided your hazard lights are on

Hazard lights are for hazards, not for a cruising speed of your own choosing. Flashing them while travelling normally tells other drivers something untrue and does not authorise the speed that made you switch them on.

On the road

Light Sunday traffic on the freeway, and a sedan holds 40 in the right lane with a train of cars queuing behind it, each pulling out to pass in turn. At the first exit it leaves, and the flow heals instantly. The minimum limit exists for that sedan: the road was built for 65, and 40 is not a safer version of the same journey — it is a different, more dangerous one.

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