Braking distance

The braking distance is the distance traveled by a vehicle from the beginning of the braking until the end of braking. The decisive factor for the length of the braking distance is the driving speed and the delay. The stopping distance is longer and takes into account the reaction time.

Stopping

The stopping distance is the distance that. A vehicle from the date on which the impediment is discovered and can be seen, travels to a standstill The recognition usually takes about 0.1 s ( for a moment ). The time of the reaction is about 0.8 s

The response (including application period ) is the period required to actuation of the brake pedal to the first contact of the brake lining with the brake disc or drum. As of this time the vehicle moves forward at a rapid speed. The response time can be shortened by reducing the clearance and by electronic sensors. The sensor and the control unit can detect an emergency braking the quick change of gas to the brake pedal and to the high speed of the braking operation. The braking is automatically initiated by this braking assistance systems, response and threshold time can be shortened by rapid pressure build-up.

The threshold time (see figure), is the time required for the brakes to develop the maximum braking effect. In a hydraulic braking system, the time between 0.1 and 0.2 seconds in the air brake system between 0.2 and 0.4 seconds. To reduce the swelling time in air brake systems, relay valves are installed bremsnah.

At a driver, the length of one second, it is assumed for the reaction and Vorbremszeit. With attentive, experienced drivers it is shorter. Drugs, alcohol and medicines they extend significantly. The reaction time largely determines the length of the necessary safety distance.

Rule of thumb ( Germany license )

With the speed v, the following rules of thumb apply.

The safety distance can impact standard with the rule of thumb

Are calculated, where k depends on the road situation. In this case (k = 1) is valid for dry roads in the local area, a minimum time of t = 1 s and in the field of t = 2 s observed. On wet pavement is about 1.5 times to twice the braking distance (k = 1,5 ... 2) and in snow and rolling split of about four times the stopping distance (k = 4 ) is required. When driving on ice, the stopping distance is still significantly longer.

At a speed v of 50 km / h on dry pavement in urban areas results

• Pathway:
• Safety distance:

Calculations and physical background

If the initial velocity in m / s and a is the constant braking deceleration in m / s ², then sB is the stopping distance ( in meters ):

Derivation of this formula:

For the speed during the braking operation the following applies:

This is the part of the velocity, which is passed through the brakes, so deceleration is lost.

For the distance traveled, the following applies:

Explanation:

Finally, the article comes to a halt, if v (t) = 0.

This one is now a in equation (2):

Solving this equation with respect to the time t is obtained as the braking time:

Substituting now the braking time in equation (3), we obtain the formula for the stopping distance:

The maximum possible deceleration depends on the friction pair tire / road.

Reference values ​​for the maximum braking deceleration of car in m / s ²:

Taking into account the deceleration of the acting perpendicular to the road component of the acceleration due to gravity, one obtains a dimensionless coefficient:

The angle of inclination of the roadway is at a positive slope.

Brakes on the inclined plane

The component of the gravitational acceleration parallel to the road adds to the acceleration due to braking. This gives the resulting delay:

As above applies to the braking distance:

If slope () and a slippery surface, the delay can be zero or negative. Then the object is not slowed down, but faster. Therefore, no braking distance can be specified.