You are towing a trailer so wide that the interior mirror shows nothing but the trailer's face. What does the law require before you may drive on the road?

Why D is correct

The mirror requirement is functional, not nominal: a driver must have an adequate view of the road to the rear, and when a trailer blocks the standard mirrors, that view must be restored with extended or trailer-towing mirrors before the combination moves. The rule exists because a driver who cannot see behind cannot merge, change lanes or judge following traffic — and a trailer makes all three both more necessary and more dangerous. Driving blind-backed behind your own cargo is not a bold choice; it is equipment the law can see you lack from a hundred metres.

Why the other options are wrong

A. You may rely on the trailer's own rear-view camera, if fitted

A camera on the trailer may help the driver who has one, but the legal duty is a rear view available to the driver; where cameras are permitted as aids, they supplement rather than replace the mirror requirement, and many trailers have no camera at all.

B. Nothing extra; the exterior mirrors satisfy every requirement

Standard exterior mirrors on a towing vehicle usually show the trailer's sides and nothing of the lanes behind, which fails the functional test the law sets. The requirement is adequacy of view, not the presence of any mirror at all.

C. You may drive provided you stay in the right lane

Lane discipline does not substitute for rear vision. Every manoeuvre that lane changes require — checking what is beside and behind you — is exactly the information a blocked mirror withholds.

On the road

Boat trailer hitched for the reservoir run, and the family sedan's mirrors frame two metres of white fibreglass each. The parts store ten minutes out of the way clips on a pair of extension mirrors, and suddenly the lane behind the boat exists again. The merge onto the highway afterwards is ordinary — which is what the ten minutes bought.

Similar questions

• Signal Before Turning | CO

  You plan to turn right from a city street into a driveway. How far in advance of the turn must you activate your turn signal?

• Colorado Mountain Traction Rules | CO

  During a winter storm, a mountain interstate corridor is placed under an active traction law for passenger vehicles. What does compliance generally require of a standard two-wheel-drive car?

• Temporary Spare Tyre Limits | CO

  After a flat, you fit the compact temporary spare from the boot. What is the correct way to treat this spare tyre?

• Headlight Aim After Loading | CO

  After loading a camper and gear, the rear of your vehicle sits low and the headlights visibly point up toward the sky. Why does this matter beyond mere inconvenience?

• Exhaust Leak Warning | CO

  During a winter drive, you notice an unusual exhaust smell in the cabin and a headache developing. What is the correct response?