PRIN.OF HIGHWAY ENGINEERING&TRAFFIC ANA.
7th Edition
ISBN: 9781119610526
Author: Mannering
Publisher: WILEY
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Chapter 2, Problem 20P
To determine
The braking efficiency of the car.
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A car is traveling at 76 mi/hr down a 3% grade on poor, wet pavement. The car's braking efficiency is 90%. The brakes were applied 320 ft before impacting an object. The car had an antilock braking system, but the system failed 200ft after the brakes had been applied (wheels locked). What speed was the car traveling at just before it impacted the object? (Assume theoretical stopping distance, ignore air resistance, and let Frl=0.015)
A driver is traveling at 90 mi/h down a 3% grade on good, wet pavement. An accident investigation team noted that braking skid marks started 410 ft before a parked car was hit at an estimated 45 mi/h. Ignoring air resistance, and using theoretical stopping distance,
a. If the car’s antilock braking system was effective (no sliding wheels on the pavement), what would the crash speed be?
part a, assuming decelerat on rate is unknown bu the friction factor=0.2.
2. A driver traveling down a 4% grade collides with a roadside object. The roadway has a posted
speed limit is 60mph. The driver mentioned he strictly followed the speed limit. The accident
investigation team indicates: braking skid marks started 300 ft before the struck object.
a. If the friction factor was measured as 0.2, estimate the speed of the vehicle when it
struck the object.
b. Estimate the minimum required friction factor so the 300 ft skid marks can allow the
driver to safely stop before he would strike the object.
Chapter 2 Solutions
PRIN.OF HIGHWAY ENGINEERING&TRAFFIC ANA.
Ch. 2 - Prob. 1PCh. 2 - Prob. 2PCh. 2 - Prob. 3PCh. 2 - Prob. 4PCh. 2 - Prob. 5PCh. 2 - Prob. 6PCh. 2 - Prob. 7PCh. 2 - Prob. 8PCh. 2 - Prob. 9PCh. 2 - Prob. 10P
Ch. 2 - Prob. 11PCh. 2 - Prob. 12PCh. 2 - Prob. 13PCh. 2 - Prob. 14PCh. 2 - Prob. 15PCh. 2 - Prob. 16PCh. 2 - Prob. 17PCh. 2 - Prob. 18PCh. 2 - Prob. 19PCh. 2 - Prob. 20PCh. 2 - Prob. 21PCh. 2 - Prob. 22PCh. 2 - Prob. 23PCh. 2 - Prob. 24PCh. 2 - Prob. 25PCh. 2 - Prob. 26PCh. 2 - Prob. 27PCh. 2 - Prob. 28PCh. 2 - Prob. 29PCh. 2 - Prob. 30PCh. 2 - Prob. 31PCh. 2 - Prob. 32PCh. 2 - Prob. 33PCh. 2 - Prob. 34PCh. 2 - Prob. 35PCh. 2 - Prob. 36PCh. 2 - Prob. 37PCh. 2 - Prob. 38PCh. 2 - Prob. 39PCh. 2 - Prob. 40P
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- A car is traveling up a 3% grade, with the speed of 85mph, on a road that has good, wet pavement. A deer jumps out onto the road and the driver applies the brakes 290-ft from it. The driver hits the deer at a speed of 20mph.If the driver did not have antilock brakes, and the wheels were locked the entire distance, would a deer-impact speed of 20mph be possible? (Hint: check the braking efficiency) [Use Theoretical Stopping Distance]arrow_forwardA level test track has a coefficient of road adhesion of 0.80, and a car being tested has a coefficient of rolling friction that is approximated as 0.018 for all speeds. The vehicle is tested unloaded and achieves the theoretical minimum stop in 180 ft (from brake application). The initial speed was 60 mi/h. Ignoring aerodynamic resistance, what is the unloaded braking efficiency?arrow_forwardA car is traveling at 60 mi/h on good, wet pavement. It has a wheelbase of 110 inches with the center of gravity 50 inches behind the front axle and at a height of 24 inches above the pavement surface. Determine the percentage of braking force that the braking system should allocate to the rear axle.arrow_forward
- A car traveling at 45 mph on a poor, wet pavement has a braking efficiency of 87%. The brakes were applied 100 feet before hitting an obstacle in the road. The road is uphill for 40 feet and then is level for the remainder of the way. The car had a maximum coefficient of road adhesion in the sloped portion of the poor, wet roadway and but as soon as it started going on the level portion its coefficient of road adhesion reduced to 0.3. Assuming that the car struck the obstacle at 30 mph, what was the grade of the hill? Assume practical stopping distance equation applies.arrow_forwardProblem 2. A car hits a tree at an estimated speed of 25 mph on a 3 % upgrade. If skid marks of 120 ft are observed on dry pavement (coefficient of braking friction, fb =0.35) followed by 250 ft (fb =0.25) on a grass stabilized shoulder, estimate the initial speed of the vehicle just before the pavement skid began.arrow_forwardA car is traveling at 70 mi/h on a level section of road with good, wet pavement. Its antilock braking system (ABS) only starts to work after the brakes have been locked for 100 ft. If the driver holds the brake pedal down completely, immediately locking the wheels, and keeps the pedal down during the entire process, how many feet will it take the car to stop from the point of initial brake application? (The braking efficiency is 80% with the ABS not working and 100 % with the ABS working. Use theoretical stopping distance and ignore air resistance. Let frl = 0.02 when the brakes are locked, but complete the frl once the ABS becomes active.)arrow_forward
- A rear-wheel-drive 2800-lb drag race car has a 170-inch wheelbase and a center of gravity 20 inches above the pavement and 140 inches behind the front axle. The owners wish to achieve an initial acceleration from rest of 22 ft/s 2 on a level paved surface. What is the minimum coefficient of road adhesion (in %) needed to achieve this acceleration? (Assume y m = 1.00.)arrow_forwarda truck was travelling uphill at 50kph. the brakes are suddenly applied and the truck stopped in a distance of 16.1m. if the coefficient of friction between the tires and the road surface is 0.4, what is the grade of the road?arrow_forwardA car is traveling up a 2% grade at 70 mi/h on good, wet pavement. The driver brakes to try to avoid hitting stopped traffic that is 250 ft ahead. The driver's reaction time is 0.5 s. At first, when the driver applies the brakes, a software flaw causes the anti-lock braking system to fail (brakes work in non-anti-lock mode with 80% efficiency), leaving 80 ft skid marks. After the 80 ft skid, the anti-lock brakes work with 100% efficiency. How fast will the driver be going when the stopped traffic is hit if the coefficient of rolling resistance is constant at 0.013? (assume minimum theoretical stopping distance and ignore aerodynamic resistance)arrow_forward
- The driver of a vehicle travelling at 80kph up a grade requires 9m less to stop after he applies the brakes than the driver travelling at the same initial speed down the same grade. If the coefficient of friction between the tires and pavement is 0.50, what is the percent grade and what is the braking distance.arrow_forwardA driver traveling down a 4% grade collides with a roadside object in rainy conditions, and is issued a ticket for driving too fast for conditions. The posted speed limit is 65 mi/h. The accident investigation team determined the following: The vehicle was traveling 40 mi/h when it struck the object, braking skid marks started 205 ft before the struck object, the pavement is in good condition, and the braking efficiency of the vehicle was 93%. Using theoretical stopping distance, assuming aerodynamic resistance is negligible, and with the coefficient rolling resistance approximated as 0.015, should the driver appeal the ticket? Why or why not?arrow_forwarda 2500-lb car designed with a 120-inch wheelbase. the center of gravity is located 22 inches above the pavement and 40 inches the front axle. if the coefficient of road adhesion is 0.6, how far back from the front axle would the center of gravity have to be to ensure that the maximum tractive effort developed for front- and rear- wheel-drive option is equal?arrow_forward
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