The question asks about a specific phenomenon observed when vehicles, particularly longer ones, make turns. It describes how the rear wheels do not follow the exact path traced by the front wheels.

Understanding Vehicle Off Tracking

When a vehicle turns, the front wheels follow a specific curve. However, due to the vehicle's length and the fixed distance between the front and rear axles, the rear wheels tend to track a path that is slightly inside the curve followed by the front wheels. This difference in path is known as "off tracking".

• Off tracking is most noticeable in sharp turns and with vehicles that have a long wheelbase (the distance between the front and rear axles).
• It is a crucial factor considered in the design of roads, intersections, and parking lots, especially for accommodating large vehicles like trucks and buses.
• Adequate lane width and turning radii are necessary to account for off tracking and ensure vehicles can navigate turns safely without running off the road or colliding with obstacles.

Based on this understanding, the phenomenon where the rear wheels do not follow the same path as the front wheels is correctly termed off tracking.

Analyzing Other Options

Let's briefly look at the other options to understand why they do not describe this phenomenon.

Extra Widening

Extra widening refers to the additional width provided to the pavement on horizontal curves. This is done primarily to counteract the effect of off tracking and provide comfortable passage for vehicles, especially larger ones, as they turn. So, extra widening is a consequence of off tracking, not the phenomenon itself.

Coning of Wheel

Coning of wheels is a term used in railway engineering, referring to the shape of the wheel treads of railway vehicles. The wheel treads are slightly tapered (coned) to help guide the wheels along the track and aid in cornering. This concept is not related to the path difference between the front and rear wheels of road vehicles.

Transition Curve

A transition curve, also known as an easement curve, is a type of curve used in road and railway alignment to gradually change the curvature from a straight section to a circular curve, or between two circular curves of different radii. It helps in the gradual application of superelevation (banking) and centrifugal force, improving rider comfort and safety. While important in road design, it does not describe the difference in path between the front and rear wheels during a turn.

Therefore, the term that accurately describes the phenomenon where the rear wheels do not follow the same path as the front wheels is off tracking.

Revision Table: Key Terms

Additional Information on Off Tracking

The amount of off tracking depends on several factors:

• Wheelbase: Longer wheelbase vehicles have greater off tracking.
• Turning Radius: Smaller turning radii (sharper turns) result in greater off tracking.
• Vehicle Type: Articulated vehicles (like semi-trailers) have complex off tracking patterns involving multiple axles.

Calculating off tracking is essential for designing geometric elements of roads, such as curve radii and intersection layouts, to ensure that all types of design vehicles can maneuver safely and efficiently.