Sight Distance

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Questions and Answers

What is the assumed brake efficiency for safe geometric design?

50% (correct)

60%

80%

70%

What is the primary factor affecting the frictional resistance between the tire and the road?

Vehicle velocity

Longitudinal friction (correct)

Reaction time

Road gradient

According to the IRC, what is the specified range of longitudinal friction values?

0.4 to 0.5

0.2 to 0.3

0.25 to 0.35

0.35 to 0.4 (correct)

What is the relationship between the gradient of the road and the required sight distance?

A steeper gradient requires a shorter sight distance Signup and view all the answers

What is the distance traveled by the vehicle during the reaction time called?

Lag distance Signup and view all the answers

Why is the sight distance required more when descending a gradient?

More time is required to stop the vehicle due to gravity Signup and view all the answers

What is the main purpose of stopping sight distance in highway design?

To provide adequate time for drivers to respond to a situation Signup and view all the answers

What is the formula for stopping sight distance (SSD) on a horizontal plane?

S = vt + 𝟐𝐠 (𝐟 ± 𝐆) Signup and view all the answers

What is the effect of a downward grade on a vehicle's stopping distance?

It increases the stopping distance Signup and view all the answers

What is the term for the distance a vehicle travels from the point of perception to the completion of deceleration?

Safe stopping distance Signup and view all the answers

What is the purpose of the perception-reaction time formula (d = vt)?

To determine the distance traveled during perception and reaction time Signup and view all the answers

What is the effect of an upward grade on a vehicle's stopping distance?

It decreases the stopping distance Signup and view all the answers

What is the primary purpose of ensuring sight distance at intersections?

To enable drivers to perceive a hazard and stop the vehicle if required Signup and view all the answers

What is the formula for sight distance on a horizontal curve when S is less than Lc?

L = 122 + 3.5S Signup and view all the answers

What is the formula to compute the passing sight distance (PSD)?

PSD = d1 + d2 + d3 + d4 Signup and view all the answers

What is the definition of Passing Sight Distance (PSD)?

The distance required for a vehicle to pass another vehicle and then return to its original lane without colliding with an oncoming vehicle. Signup and view all the answers

What is the primary purpose of the distance d1 in the passing sight distance calculation?

To allow the passing vehicle to travel while accelerating to the point of encroachment on the left lane Signup and view all the answers

What is the relationship between Intermediate Sight Distance (ISD) and Stopping Sight Distance (SSD)?

ISD is twice SSD. Signup and view all the answers

What is the significance of the distance d4 in the passing sight distance calculation?

It is the distance that the opposing vehicle travels during the final 2/3 of the period when the passing vehicle is in the left lane Signup and view all the answers

What is the unit of measurement for L in the formula L = 122 + 3.5S?

Meters Signup and view all the answers

How is the stopping sight distance for each road typically computed?

From the design speed of the road Signup and view all the answers

What is the variable M in the formula R = 8M / AS^2?

Clear distance from the center of the roadway to the obstruction Signup and view all the answers

What is the relationship between the headlamp sight distance and the height of the beam of a vehicle's head lamp?

The headlamp sight distance is directly proportional to the height of the beam of a vehicle's head lamp Signup and view all the answers

What is the purpose of calculating sight distance on a horizontal curve?

To ensure safe overtaking on a horizontal curve Signup and view all the answers

What is the primary purpose of headlamp sight distance during night driving?

To enable drivers to perceive hazards in all directions Signup and view all the answers

What is the condition when the design of sight distance at intersections is not necessary?

When there is a stoplight at the intersection Signup and view all the answers

What is the unit of measurement for θ in the formula for headlamp sight distance?

Radians Signup and view all the answers

What is the effect of increasing the height of the headlamp above the road surface?

It increases the headlamp sight distance Signup and view all the answers

What is the primary purpose of enabling stopped vehicles to cross a main road?

To prevent accidents at intersections Signup and view all the answers

What is the assumption made when designing sight distance at intersections with a stoplight?

All traffic is stopped except for the driver's lane and opposing lane Signup and view all the answers

Study Notes

Headlamp Sight Distance

Headlamp sight distance is the distance visible to a driver during night driving under the illumination of headlamps/lights.
It is critical at up- gradients and at the ascending stretch of valley curves.
The distance should enable the driver to perceive a hazard not only in the forward direction but also to the left and right.

Design of Sight Distance at Intersections

The design of sight distance at intersections is based on three possible conditions.
When S > L, the formula is S > √(h² + S²θ)
When S < L, the formula is L = √(h² + S²θ)
Where L is the length of the curve, S is the headlamp sight distance, h is the height of the headlamp above the road surface, and θ is the angle of beam tilts upward above the horizontal axis of the car.

Stopping Sight Distance (SSD)

SSD is the minimum sight distance available on a highway at any spot, having sufficient length to enable the driver to stop a vehicle traveling at design speed, safely without collision with any other obstruction.
The formula for SSD is S = vt + √(v² / (g(f ± G))), where v is the running speed, t is the perception-reaction time, g is the acceleration due to gravity, f is the coefficient of friction, and G is the gradient of the road.

Factors Affecting Stopping Sight Distance

Frictional resistance between the tire and the road affects SSD.
When the frictional resistance is more, the vehicles stop immediately, and the sight required will be less.
The gradient of the road also affects SSD.
While climbing up a gradient, the vehicle can stop immediately, and the sight distance required is less.
While descending a gradient, gravity also comes into action, and more time will be required to stop the vehicle, resulting in a longer SSD.

Intermediate Sight Distance (ISD) and Passing Sight Distance (PSD)

ISD is defined as twice the SSD.
PSD is the shortest distance sufficient for a vehicle to turn out of a traffic lane, pass another vehicle, and then turn back to the same lane safely and comfortably without interfering with the overtaken vehicle or an incoming vehicle traveling at design speed.
PSD can be divided into four quantifiable portions: d1, d2, d3, and d4.

Sight Distance on Horizontal Curves

When S < L, the formula is S² = R(8M² + 3.5S)
When S > L, the formula is L = √(S² - M²)
Where S is the sight distance, R is the radius of the curve, and M is the clear distance from the center of the roadway to the obstruction.

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