What does a sign that indicates 'start of a motorway' imply?

A sign indicating the 'start of a motorway' signifies that specific regulations and rules governing the use of motorways will come into effect at that point. This means that drivers must adhere to all motorway regulations, which can include speed limits, lane usage, and various driving behaviors that are distinct from regular roads. Such rules are designed to enhance safety and efficiency on high-speed, multi-lane roads and can include aspects like prohibitions on stopping except in emergencies and requirements to use indicated lanes appropriately.

The other options do not accurately reflect what the sign conveys. A sign indicating 'start of a motorway' does not suggest that there is no entry to the motorway; instead, it actively invites drivers to merge onto the motorway. It also does not require immediate lane changes, nor does it indicate any specific restrictions on overtaking. The primary focus of this sign is to communicate that drivers are entering a distinct driving environment with its own set of guidelines to follow.