15.4.2. Psychological widening

Widening of pavements has to be done for some psychological reasons also. There is a tendency for the drivers to drive close to the edges of the pavement on curves. Some extra space is to be provided for more clearance for the crossing and overtaking operations on curves.

Psychological widening is an essential aspect of road design that considers the behavior of drivers on curves. When vehicles navigate a bend, drivers often feel compelled to drive closer to the edge of the pavement. This tendency makes it critical to design wider curves than what mechanical factors alone would dictate. Providing extra space on turns allows drivers to maneuver more comfortably while crossing or overtaking other vehicles, which enhances overall safety.

Imagine driving on a winding mountain road. As you navigate each curve, you might unconsciously steer closer to the edge of the road because of the visual cues and the way the road turns. To feel safer, road engineers add extra width to these curves, similar to how you might choose a larger path when walking around a corner to avoid bumping into anyone.

IRC proposed an empirical relation for the psychological widening at horizontal curves: Wps = v / (2.64√R)

The IRC (Indian Roads Congress) has derived a specific formula to calculate the psychological widening needed for road curves based on vehicle speed (v) and the radius of the curve (R). The formula indicates that as the speed increases, or as the radius of the curve decreases, the psychological widening required increases. This relationship helps road designers ensure that curves are adequately safe for higher speeds and tighter turns.

Think of riding a bicycle around a bend. If you're going fast and the turn is sharp (a smaller radius), you'll want more space to keep from falling off. The formula used by road planners is like understanding that your need for extra room grows with speed and tightness of the curve.

Therefore, the total widening needed at a horizontal curve W is: W = We + Wm + Wps, where We, Wm, and Wps represent the extra width for superelevation, mechanical widening, and psychological widening respectively.

The total widening required at a horizontal curve includes three components: extra width for superelevation (We), mechanical widening (Wm), and psychological widening (Wps). This comprehensive approach ensures that the road is wide enough not just for the physical dimensions of vehicles, but also for the behaviors of drivers and the dynamic conditions during turns.

Consider a race track. Drivers need enough space for their cars to grip the road (mechanical), they may adjust their positions based on their confidence (psychological), and the track itself features banked turns (superelevation) to help maintain speed. The total width of the track must accommodate all these factors to ensure safety and performance.

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