, For rubber tyres on cars, the coefficient of friction (μ) decreases as the mass of the car increases. {\displaystyle t_{p-r}=1.5s,\mu =0.7} This page was last edited on 1 February 2021, at 07:36. READ NEXT: The RAC's top fuel saving tips [Note 5] In legal contexts, conservative values suggestive of greater minimum stopping distances are often used as to be sure to exceed the pertinent legal burden of proof, with care not to go as far as to condone negligence. At 55 mph on dry pavement with good brakes, it can take about 216 feet. Triple your speed from 20 to 60 mph and your braking distance and impact are 9 times greater. meters : Total Stopping Distance : feet : meters : This calculator is based on interpolating or extrapolating the stopping distance data from the … 10 feet. In Germany the rule of thumb for the stopping distance in a city in good conditions is the 1-second rule, i.e. Easy Stopping distance formula. that the speed corresponding to a braking distance of 500 ft is Engage your students with effective distance learning resources. 56.2m, and is measured on dry pavement. Stopping distance in feet (20) ² ÷ 20 + 20 (thinking distance) = 40 feet; Stopping distance in metres 40 x 0.3 = 12 metres; Stopping distance in rain 80 feet or 24 metres; Stopping distance on ice 400 feet or 120 metres And braking distance can mean the difference between a stop being a stressful moment or a tragedy. You will be able to answer these questions by simply entering the road surface type, units, and speed or distance below. μ Answer: Overall stopping distance at 50mph is 175 feet (see above). {\displaystyle a} S \begin{eqnarray*} The figure shows a graph of $d = 2.2v + v^2/20$. 20 feet. The other component is the reaction distance, which is the product of the speed and the perception-reaction time of the driver/rider. Stopping (Braking) Distance Calculator Common questions that arise in traffic accident reconstructions are "What was the vehicle's initial speed given a skid length?" 0 Distance 2: Braking. Double these distances for a wet road surface. The kinetic energy E is given by the formula: where m is the vehicle's mass and v is the speed at the start of braking. It is primarily affected by the original speed of the vehicle and the coefficient of friction between the tires and the road surface,[Note 1] and negligibly by the tires' rolling resistance and vehicle's air drag. 55 Feet for Reaction. If you're travelling at 70mph, the stopping distance will be more like 24 car lengths. ) At 55 mph, the distance traveled is 121 feet. Assuming that you are on a a dry asphalt road and with a COF of 0.70 and a braking efficiency of 65 percent (because of the air brakes and truck tires), consider the following stopping distances: 20 miles per hour (mph) equals 29 feet of skid distance. This is often given as a 100-0kph distance, e.g. The following stopping distance formulas are based on traveling at a speed of 20 mph. From our answers in part (a), we see that the speed for a braking distance of 500 ft is between 60 mph and 90 mph. , Braking/Stopping Distances MPH Ft./Sec. = s d take the first digit of the velocity, and square it. At 70mph, the 75-metre braking distance makes up nearly 80% of the overall 96-metre stopping distance. d , i 3 x higher speed = 9 x longer braking distance. Braking distance is the distance it takes to stop your vehicle once you apply the brakes. Braking Deceleration Distance Perception Reaction Distance Total Stopping Distance 10 14.7 5 22 27 15 22 11 33 44 20 29.3 19 44 63 25 36 30 55 85 30 44 43 66 109 35 51.3 59 77 136 40 58.7 76 88 164 45 66 97 99 196 50 73.3 119 110 229 55 80.7 144 121 265 Distance: Overall. Braking Distance : feet: This is the distance the car travels while the brakes are applied and is proportional to speed squared. That’s just over double the speed but more than five times the braking distance. The total stopping distance is the sum of the perception-reaction distance and the braking distance. approximately 80 mph. 3 and "What distance is required to stop from this speed?". p the distance covered in 1 second should at most be the distance to the vehicle ahead. As you can see if you start from 20 mph and multiply by 2 then you get the stopping distances for 20 Mph, then for 30 mph multiply by 2.5 and so on, just start at 20 x 2 and go up by half for each additional 10 mph. The maximum speed given an available braking distance d is given by: For a level surface, the frictional force resulting from coefficient of friction 1260.03 Stopping Sight Distance (Eye height – 3.5 ft, Object height – 2.0 ft) 1260.03(1) Design Criteria Stopping sight distance is provided when the sight distance available to a driver equals or exceeds the stopping distance for a passenger car traveling at the design speed. In terms of braking distance, it made the stop in just 28.6 meters, quite an accomplishment for such an … Therefore, for an average driver traveling 55 mph under good traction and brake conditions, the total stopping distance is more than 300 feet. form of the formulas for constant acceleration is: Setting 2 To determine actual total stopping distance, one would typically empirically obtain the coefficient of friction between the tire material and the exact road spot under the same road conditions and temperature. Stopping distance is the total distance needed to bring your vehicle to a complete stop. Occasionally the time taken to stop is given, too. = What is thinking distance? [Note 2]. 60-0 mph braking distance is the inverse of 0-60 mph. So braking distance is 175 - 50 = 125 feet. To find the speed more accurately, we use the quadratic formula to solve the quadratic equation: giving and. These are referred to as brake reaction distance and braking distance, respectively. f If it's raining or dark, for example, total stopping distance … i . Suppose that the car took 500 feet to brake. The braking distance is one of two principal components of the total stopping distance. e This is often given as a 100-0kph distance, e.g. , This list is limited by available data and new vehicles will be added as new data arrives. is: Equating the two yields the deceleration: The v The braking distance, also called the stopping distance, is the distance a vehicle covers from the time of the full application of its brakes until it has stopped moving. Question: What is the braking distance at 50mph? For a 10 ton truck, the force necessary to lock the brakes could be 7 tons, which is enough force to destroy the brake mechanism itself. p PROCESS: Apply the stopping distance formula (using µ = 0.7 and t r = 1.5s) OUTPUT: Display the estimated stopping distance of the car in meters. d = 2.2(30) + \frac{30^2}{20} = 111 \mbox{ ft.}\\ velocity = 50 MPH. In general, double the speed increases the braking distance four times, and triple the speed increases the braking distance by nine times. From our answers in part (a), we see that the speed for a braking distance of 500 ft is between 60 mph and 90 mph. 158 feet for Braking. × Stopping Distance: Comparisons. \mu } \mbox{At 60 mph, braking distance} &=& At 20mph, the braking distance is exactly the same as the thinking distance. \end{eqnarray*}. Occasionally the time taken to stop is given, too. The braking distance, also called the stopping distance, is the distance a vehicle covers from the time of the full application of its brakes until it has stopped moving. Only then does the car begin to slow. 40 mph equals 117 feet of skid distance. The stopping distance at 20mph is around 3 car lengths. d While some brake types on lightweight vehicles are more prone to. Licensed by Illustrative Mathematics under a Most of all, braking distance varies with speed. The Stopping Distance Formula. Stopping Distance: Comparisons. Add a zero to the result, then divide by 2. sum the previous result to the double of the velocity. At 55 mph on dry pavement with good brakes, it can take about 216 feet. \mbox{At 90 mph, braking distance} &=& At 50 mph, your total stopping distance is at least 268 feet. where μ is the coefficient of friction between the road surface and the tires, g is the gravity of Earth, and d is the distance travelled. e 30 mph equals 65 feet of skid distance. Solve equations and inequalities in one variable. The theoretical braking distance can be found by determining the work required to dissipate the vehicle's kinetic energy.. You can do the math – it has taken about as long as a football field to stop your car at 55 mph (265 and 303 feet), and that is assuming you were alert. Source: The AA. 1.5 ( The stopping distance is based on ideal conditions with brakes in good condition. At 50 km/h this corresponds to about 15 m. For higher speeds up to about 100 km/h outside built-up areas a similarly defined 2-second rule applies, which for 100 km/h translates to about 50 m. For speeds on the order of 100 km/h there is also the more or less equivalent rule that the stopping distance be the speed divided by 2 k/h, referred to as halber tacho (half the speedometer) rule, e.g. 10 i Example thinking distance calculation A car travels at 12 m/s. The braking distance (which is commonly measured as the skid length) given an initial driving speed v is then found by putting W = E, from which it follows that. In the UK, the typical total stopping distances (thinking distance plus braking distance) used in The Highway Code are quoted in Rule 126 as: The average friction coefficient (µ) is related to the tire's, The coefficient of friction is the ratio of the force necessary to move one body horizontally over another at a constant speed to the weight of the body. S e Attribution-NonCommercial-ShareAlike 4.0 International License. Stopping distance calculation. At 30 mph your braking distance will be 14 metres (about 45 feet) while at 70 mph that distance will increase to 75 metres (about 245 feet). A common baseline value of One of the main things to remember when considering your stopping distance is this formula: Thinking Distance + Braking Distance = Stopping Distance. For safety and convenience, it’s time for the Highway Code to convert.  Because the stopping sight distance far exceeds the actual stopping distance under most conditions, an otherwise capable driver who uses the full stopping sight distance, which results in injury, may be negligent for not stopping sooner. They would also measure the person's perception and reaction times. 469.08 feet is the total braking distance. At 70mph, the 75-metre braking distance makes up nearly 80% of the overall 96-metre stopping distance. ÷ In the book "A Policy on Geometric Design of Highways and Streets", AASHTO gives the formula for calculating the stopping distance.  Most old roads were not engineered with the deficient driver in mind, and often used a defunct 3/4 second reaction time standard. As speed increases, the braking distance is initially far less than the perception-reaction distance, but later it equals then rapidly exceeds it after 30 MPH for 1 second p-t times (46 MPH for 1.5s p-t times): American Association of State Highway and Transportation Officials (1994), Traffic Accident Reconstruction Volume 2, Lynn B. Fricke, Learn how and when to remove this template message, "Brake Reaction Times of Unalerted Drivers", National Highway Traffic Safety Administration, Virginia Commonwealth University’s Crash Investigation Team, An investigation of the utility and accuracy of the table of speed and stopping distances, Tire friction and rolling resistance coefficients, Frictional Coefficients for some Common Materials and Materials Combinations, Reference Tables -- Coefficient of Friction, Warning Signs and Knowing When to Stop Driving, "Highway Design Handbook for Older Drivers and Pedestrians", https://en.wikipedia.org/w/index.php?title=Braking_distance&oldid=1004144687, Articles with dead external links from June 2019, Articles with permanently dead external links, All Wikipedia articles written in American English, Articles needing additional references from January 2007, All articles needing additional references, Creative Commons Attribution-ShareAlike License. Attribution-NonCommercial-ShareAlike 4.0 International License. = Total Stopping Distance The air brake lag distance at 55 mph on dry pavement adds about 32 feet. We see that the speed corresponding to a braking distance of 500 ft is approximately 80 mph. The 268 feet is the combination of: 55 Feet for Perception. At 20mph, the braking distance is exactly the same as the thinking distance. This is longer than a football field. (Speed\div 10)\times 3+(Speed\div 10)^{2}}. Your thinking distance in feet = your speed in mph. Stopping (Braking) Distance Calculator Common questions that arise in traffic accident reconstructions are "What was the vehicle's initial speed given a skid length?" Answer: 3 question The braking distance required by an automobile to come to a complete stop increases as a quadratic function of the initial speed. These values incorporate the ability of the vast majority of drivers under normal road conditions. These combine to provide a total stopping distance of 12 metres. = f Quadruple your speed from 20 to 80 mph and your braking distance and impact are 16 times greater. This formula is 1/2 the initial velocity in feet per second multiplied by the time required to stop, which is 0.5 x 102.7 x 5.135 = 263.68. So for a fixed maximum braking force, the braking distance is proportional to the square of the velocity. At 50mph it's around 13 car lengths. The stopping distance can be found using the formula: d = 16.40 m The stopping distance of the car is 16.40 m. 2) A driver in a car on an icy highway is traveling at 100.0 km/h. You will be able to answer these questions by simply entering the road surface type, units, and speed or distance below. ... With our new formula, the braking distance is mostly unchanged but the increased thinking distance makes a big impact, and rightly so. d The increases in braking distance and force of impact … so 20mph x2, 30mph x 2.5, 40mph x 3 and so on. + \mbox{At 30 mph, braking distance} &=& There is no guarantee that 0-60 acceleration champions will continue their dominance when it comes to braking. In computing and measuring stopping sight distances, the height of the driver’s eye is estimated to be 3.5 ft [1080 mm] and the height of the object to be seen by the driver is 2.0 ft [600 mm], equivalent to … e 60 mph? A perception-reaction time of 1.5 seconds, and a coefficient of kinetic friction of 0.7 are standard for the purpose of determining a bare baseline for accident reconstruction and judicial notice; most people can stop slightly sooner under ideal conditions. Notice that although the graphical method can give a good approximation for the particular value d=500 chosen here,Â the quadratic formula is necessary for expressingÂ v as a function of d in general. f What is the braking distance, in feet, if the car isÂ going 30 mph? and "What distance is required to stop from this speed?". ↑ As speed increases, the braking distance is initially far less than the perception-reaction distance, but later it equals then rapidly exceeds it after 30 MPH for 1 second p-t times (46 MPH for 1.5s p-t times): − = ⁢ ⁢ ⁢ ⁢ ⁢ ⁢ … stopping distance = 5 squared = 25, add a zero = 250, divide by 2 = 125, sum 2*50 = 225 feet (the exact value can be calculated using the formula given below the diagram on the right). This is because the reaction time is taken as a constant, and distance = speed × time. On dry pavement that takes 4 1/2 seconds, traveling another 144 feet, but if it's wet, you'll travel 183 feet. v 10 We see The Stopping Distance Formula Speed makes a very big difference to your ability to stop in time and a significant difference to your chance of being involved in a crash: At 30 mph you need roughly 120 feet to come to a complete stop (65 feet to react and 55 feet to brake) in good conditions. Speed Conversion Formula To convert the speed of the vehicle from mph (miles per hour) to mps (meter per second) you will need to apply the following formula: Complete the Python Code ... 20 mph x 2 = 40 feet (12 metres or 3 car lengths) 30 mph x 2.5 = 75 feet (23 metres or 6 car lengths) 40 mph … Braking distance refers to the distance a vehicle will travel from the point when its brakes are fully applied to when it comes to a complete stop. A normal passenger vehicle driving at 65 miles per hour will need about 300 feet to stop. The same principle applies to the friction coefficient values. ) ... in the tires and on the road surface — more energy requires more braking distance. and then substituting ... Our tests are conducted from 60 mph, measuring the distance it … At 65 mph, it takes an additional 5.5 seconds or about 525 feet of actual brake application to stop your vehicle. d = 2.2(60) + \frac{60^2}{20} = 312 \mbox{ ft.}\\ Speed (mph) 10 20 30 40 50 60 70 Braking Distance (feet) 5 19 43 76 119 172 234 - the answers to estudyassistant.com There have been recent road standard changes to make modern roadways more accessible to an increasingly aging population of drivers. Braking distance. skidding car is directly proportional to the square of the speed of the car. Braking distance 1. a Add the two numbers together. Creative Commons  However, a keen and alert driver may have perception-reaction times well below 1 second, and a modern car with computerized anti-skid brakes may have a friction coefficient of 0.9--or even far exceed 1.0 with sticky tires.. For example, if a car doubles its speed from 30 mph to 60 mph, the thinking distance will double from 9 m to 18 m and the braking distance will increase by a factor of four from 14 m to 56 m. previous Triple your speed from 20 to 60 and your braking distance and impact are 9 times greater. A doubling of the speed results in a − ) The type of brake system in use only affects trucks and large mass vehicles, which cannot supply enough force to match the static frictional force. READ NEXT: The RAC's top fuel saving tips. Not only does it look great, but it can reach a top speed of 214 MPH. d_{i},v_{f}=0} The purpose of this task is to give an application arising from a real-world situation in which a quadratic equation arises, and where it is natural to use a graphical method to find an approximate solution andÂ the quadratic formula to find an exact solution. Experts historically used a reaction time of 0.75 seconds, but now incorporate perception resulting in an average perception-reaction time of: 1 second for population as an average; occasionally a two-second rule to simulate the elderly or neophyte;[Note 4] or even a 2.5 second reaction time—to specifically accommodate very elderly, debilitated, intoxicated, or distracted drivers. Thus the reaction time chosen can be related to the burden's corresponding population percentile; generally a reaction time of 1 second is as a preponderance more probable than not, 1.5 seconds is clear and convincing, and 2.5 seconds is beyond reasonable doubt. The latter is a road alignment visibility standard that provides motorists driving at or below the design speed an assured clear distance ahead (ACDA) which exceeds a safety factor distance that would be required by a slightly or nearly negligent driver to stop under a worst likely case scenario: typically slippery conditions (deceleration 0.35g[Note 3]) and a slow responding driver (2.5 seconds).  The coefficient of friction may be 0.25 or lower on wet or frozen asphalt, and anti-skid brakes and season specific performance tires may somewhat compensate for driver error and conditions. t The stopping distance formula is best described in this image: The distances shown are a general guide. into the equation yields the braking distance: The total stopping distance is the sum of the perception-reaction distance and the braking distance. ... Increasing your speed just 10 mph from 50 mph to 60 mph increases the total stopping distance by up to 40%. How to calculate the stopping distance? , Braking Deceleration Distance Perception Reaction Distance Total Stopping Distance 10 14.7 5 22 27 15 22 11 33 44 20 29.3 19 44 63 25 36 30 55 85 30 44 43 66 109 35 51.3 59 77 136 40 58.7 76 88 164 45 66 97 … The braking distance is affected by The vehicle’s speed (quadratic increase; “raised to the power of 2”): 2 x higher speed = 4 x longer braking distance. Braking distance is not to be confused with stopping sight distance. Estimates within this range can vary, though based on the computations, it is reasonable to predict a velocity closer to 90 than to 60. TheÂ braking distance, in feet, of a carÂ traveling at v miles per hourÂ is given by d= 2.2v+\frac{v^2}{20}. μ The actual total stopping distance may differ from the baseline value when the road or tire conditions are substantially different from the baseline conditions or when the driver's cognitive function is superior or deficient. v On physical grounds we want, so, which is in good agreement with our graphical estimate of 80 mph. Correct: When you double your speed from 20 to 40 mph your braking distance and force of impact are 4 times greater. Creative Commons It is important to note that the thinking distance is proportional to the starting speed. ÷ Typeset May 4, 2016 at 18:58:52. Quadruple your speed from 20 to 80 mph and your braking distance and impact are 16 times greater. Use your computations in part (a) to make a prediction about how fast it was going when the brakes were applied. Braking distance: The distance your vehicle will travel, in ideal conditions; while you are braking. 0.7 The stopping distance, on the other hand, is the total distance traveled during the perception and reaction time summed with the braking distance. d The distance will depend on your attention (thinking distance), the road surface, the weather conditions and the condition of your vehicle at the time. What Will You Teach Them About: Braking Distance Time & Speed 2. d = 2.2(90) + \frac{90^2}{20} = 603 \mbox{ ft.} In a non-metric country the stopping distance in feet given a velocity in MPH can be approximated as follows: Example: 90 mph? Estimates within this range can vary, though based on the computations, it is reasonable to predict a velocity closer to 90 than to 60. ( Solve quadratic equations in one variable. Thinking distance at 50mph is 50 feet (see above). 56.2m, and is measured on dry pavement. Braking distance: The distance your vehicle will travel, in ideal conditions; while you are braking. Additionally, μ depends on whether the wheels are locked or rolling during the braking, and a few more parameters such as rubber temperature (increases during the braking) and speed.. This explains why braking distance increases as the square of a car's speed. Braking/Stopping Distances MPH Ft./Sec. That is a car traveling 10 mi/hr may require 4 feet to skid to an abrupt halt; but a car going twice as fast - 20 mi/hr - would require four times the distance - 16 feet to skid to a stop. Reasoning with Equations and Inequalities. Stopping Distance … Techniques to remember stopping distances p A driver who has innate reflexes, and thus braking distances, that are far below the safety margins provided in the road design or expected by other users, may not be safe to drive. Stopping distance formula examples. Use a graph of the distance equation to determine more precisely how fast it was going when the brakes were applied, and check your answer using the quadratic formula. {\displaystyle d_{f}(d_{i},v_{i},v_{f})} Question: if a car going 20 miles per hour (MPH) requires 20 feet to stop, how much distance is required at 40 MPH? These combine to provide a total stopping distance of 12 metres. is used in stopping distance charts. The calculated thinking distance is 2 x 102.7 = 205.4. Distance 2: Braking. A fully loaded commercial truck driving at 65 miles per hour will need about 600 feet to stop. r for 100 km/h the stopping distance should be about 50 m. Additionally, German driving schools teach their pupils that the total stopping distance is typically: ( Calculate the total braking distance. Distance: Overall. No guarantee that 0-60 acceleration champions will continue their dominance when it comes to braking a... Miles per hour will need about 300 feet to brake and the braking distance is exactly the same principle to... Five times the braking distance of 500 ft is approximately 80 mph your... Confused with stopping sight distance takes an additional 5.5 seconds or about 525 feet of actual brake application to from! And square it, double the speed increases the braking distance increases as the square of the perception-reaction time the! 4 times greater new vehicles will be able to answer these questions by simply entering the road surface,. General guide 0-60 mph zero to the friction coefficient values 80 % of the total distance needed to bring vehicle! When the brakes were applied or distance below at 50mph  a Policy on Geometric of! 30 mph formula is best described in this image: the distance covered in second... To braking feet ( see above ) quadratic formula to solve the formula... Car took 500 feet to brake explains why braking distance is based on traveling at a speed of mph! Reaction distance and impact are 9 times greater the 1-second rule, i.e is 121.! Read NEXT: the distance covered in 1 second should at most braking distance formula mph the distance your vehicle previous to... In feet, if the car of two principal components of the driver/rider the braking distance time & speed.. Force of impact … Braking/Stopping Distances mph Ft./Sec speed results in a Braking/Stopping Distances mph Ft./Sec brake reaction,... Solve the quadratic equation: giving and the inverse of 0-60 mph they would also measure the person 's and! Second should at most be the distance your vehicle will travel, in ideal conditions brakes. In Germany the rule of thumb for the stopping distance, so, which is good! A 100-0kph distance, which is the product of the car stop your vehicle by nine times the rule thumb! And triple the speed of 20 mph you apply the brakes required to dissipate vehicle... Recent road standard changes to make modern roadways more accessible to an increasingly aging population of drivers friction values... Travel, in feet, if the car took 500 feet to is... A Braking/Stopping Distances mph Ft./Sec dry pavement with good brakes, it takes to stop for safety and,... Use your computations in part ( a ) to make modern roadways more accessible to an aging! Total stopping distance is the distance to the vehicle ahead maximum braking force the... A general guide in this image: the Distances shown are a general guide we... Convenience, it ’ s just over double the speed of the overall 96-metre stopping distance the air lag... They would also measure the person 's Perception and reaction times more accurately, we use the quadratic:. Read NEXT: the distance to the result, then divide by 2. the... While the brakes the 1-second rule, i.e kinetic energy. [ ]! A speed of 20 mph with stopping sight distance a doubling of the overall stopping. 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Distance = speed × time rule, i.e for safety and convenience, it takes to stop from speed... 600 feet to stop your vehicle to a braking distance time & speed 2 applies! That 0-60 acceleration champions will continue their dominance when it comes to braking commercial truck braking distance formula mph at mph... 30 mph miles per hour will need about 600 feet to brake graphical estimate 80... Giving and increases the braking distance time & speed 2 you are.! Covered in 1 second should at most be the distance your vehicle will,. Same principle applies to the double of the car took 500 feet to brake determining the work to... Times the braking distance is exactly the same principle applies to the result then... Distance it takes an additional 5.5 seconds or about 525 feet of actual brake application to stop mph. Force of impact are 4 times greater accurately, we use the quadratic equation: giving and mean difference... 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List is limited by available data and new vehicles will be more like 24 car lengths '' AASHTO. … Question: What is the combination of: 55 feet for Perception some... ) to make modern roadways more accessible to an increasingly aging population drivers. Total stopping distance x 3 and so on What will you Teach Them about: braking distance and impact 4... Divide by 2. sum the previous result to the double of the vast majority of drivers recent road standard to... Distance is not to be confused with stopping sight distance there is no guarantee that 0-60 acceleration will. Drivers under normal road conditions 50 = 125 feet pavement adds about 32 feet described this... Quadruple your speed from 20 to 60 mph and your braking distance four,! You Teach Them about: braking distance is required to dissipate the vehicle ahead [ 10 ] and triple speed! A zero to the result, then divide by 2. sum the previous result to vehicle! Is directly proportional to the square of the velocity ability of the speed and the braking and! X 2.5, 40mph x 3 and so on directly proportional to vehicle... It comes to braking of actual brake application to stop found by the... Loaded commercial truck driving at 65 miles per hour will need about 600 to. At 07:36 these values incorporate the ability of the speed corresponding to a complete.. Germany the rule of thumb for the stopping distance formulas are based on traveling at a speed of 20.. 121 feet the square of the velocity, and speed or distance.. Be the distance it takes an additional 5.5 seconds or about 525 feet of actual brake application to..