Traffic and Highway Engineering
5th Edition
ISBN: 9781305156241
Author: Garber, Nicholas J.
Publisher: Cengage Learning
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Question
Chapter 4, Problem 6P
To determine
The speed of the road, estimate of 85th percentile speed.
Expert Solution & Answer
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For a spot speed study in which 100 observations were obtained, the mean speed was 52km/h and the standard deviation was 4.6 km/h.
1.What is the margin of error on the estimate of true mean speed obtained from this sample?
2.What is a reasonable estimate of the 85th percentile speed based on the information available?
Use N = ( )2 in your determinations. In addition read up on 85th percentile speed.
3
During a traffic speed survey, the following observations were recorded when a vehicle passes a
50 m long road section XY.
Vehicle Time of Passing X (seconds) Time of Passing Y (seconds)
1
4.5
5.8
6.1
6.3
7.5
23
4
5
2.0
3.5
4.0
4.5
5.5
Determine the following:
(i) Average time mean speed
(ii) Average space mean speed using the above data
(iii) Also verify the results obtained in (ii) above using relationship between the time mean speed
and space mean speed.
For a spot speed study in which 100 observations were obtained, the mean speed was 52 km/h and the standard deviation was 4.6 km/h. (BO0K: Traffic % Highway engineering, N. Gruber SI unit)
What is the margin of error on the estimate of true mean speed obtained from this sample?
What is a reasonable estimate of the 85th percentile speed based on the information available?
Chapter 4 Solutions
Traffic and Highway Engineering
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- Speed data collected on an urban roadway yielded a standard deviation in speeds of 4.8 mi/h. (a) If an engineer wishes to estimate the average speed on the roadway at a 95% confidence level so that the estimate is within 2 mi/h of the true average, how many spot speeds should be collected? (b) If the estimate of the average must be within 1 mi/h, what should the sample size be?arrow_forwardengineer wishing to determine the travel time and average speed along a section of an urban highway as part annual trends analysis on traffic operations conducted a travel time study using the floating -car technique .He carried out 10 runs and obtained a standard deviation of +-3 mi/h in the speeds obtained .if 5% significance level is assumed is the number of test runs adequate?arrow_forwardThe data shown below were obtained by time-lapse photography on a highway. Use regression analysis to fit these data to the Greenshields model and determine the following. Speed (mi/h) Density (veh/mi) 16.7 84 25.7 69 35.2 54 43.1 40 54.4 19 56.1 14 (a) the mean free speed (in mi/h) mi/h (b) the jam density (in veh/mi) veh/mi (c) the capacity (in veh/h) veh/h (d) the speed at maximum flow (in mi/h) mi/harrow_forward
- An engineer, wishing to determine the travel time and average speed along a sectionof an urban highway as part of an annual trend analysis on traffic operations, conducteda travel time study using the floating-car technique. He carried out 10 runs andobtained a standard deviation of ±3 mi/h in the speeds obtained. If a 5% significancelevel is assumed, is the number of test runs adequate?arrow_forwardAn engineer, wishing to determine the travel time and average speed along a section of an urban highway as part of an annual trend analysis on traffic operations, conducted a travel time study using the floating-car technique. He carried out 10 runs and obtained a standard deviation of ±3.4 mi/hin the speeds obtained. If a 5 percent significance level is assumed, is the number of test runs adequate?arrow_forwardThe data shown below were obtained by time-lapse photography on a highway. Use regression analysis to fit these data to the Greenshields model and determine The mean free speed The jam density The capacity The speed at maximum flow Speed(mi/h) Density (veh/mi) 14.2 85 24.1 70 30.3 55 40.1 41 50.6 20 55 15arrow_forward
- Q3. The below Table shows the time and distance for 10 vehicles recorded during a traffic survey. Choose the correct answer of the following (Four only): 1. The Average Spot Speed of the sample in the Table equals: a. (68.5) Km/hr c. (19.21) Km/hr e. (18.9) Km/hr (20 Marks Time (sec) 5.0 Distance (m) b. (190.21) Km/hr d. (67.9) Km/hr f. None of them Distance/time (m/sec) 20.00 100 5.6 100 17.86 5.6 100 17.86 4.8 100 20.83 2. The Time Mean Speed (TMS) of the sample in the Table equals: a. 68.5 (Km/hr) c. 19.21 (Km/hr) e. 18.9 (Km/hr) 6.1 100 16.39 5.3 100 18.87 b. 190.21 (Km/hr) d. 67.9 (Km/hr)- f. None of them 5.9 100 16.95 5.2 100 19.23 4.5 100 22.22 5.0 100 20.00 3. The Space Mean Speed (SMS) of the sample in the Table equals: a. 68.5 (Km/hr) d. 67.9 (Km/hr) Total 53 1000 190.21 b. 190.21 (Km/hr) e. 18.9 (Km/hr) c. 19.21 (Km/hr) f. None of them 4. The Average travel Speed of the sample in the Table equals: a. 68.5 (Km/hr) d. 67.9 (Km/hr) b. 190.21 (Km/hr) e. 18.9 (Km/hr) c. 19.21…arrow_forwardTwo sets of students are collecting traffic data at two sections, xx and yy, of a highway 1,200 ft apart. Observations at xx show that five vehicles passed that section at intervals of 3, 4, 3, and 5 sec, respectively. If the speeds of the vehicles were 55, 50, 45, 40, and 35 mi/h, respectively, determine the space mean speed (in km/h) for the data using the following equation where ut and us are in km/h. (Round your answer to at least three significant figures.) ut = 0.966us + (3.541 km/h) km/h Determine the space mean speed (in km/h) for the data using the following equation. (Round your answer to at least three significant figures.) us = n n 1 ui i=1 km/h Compare your answers and discuss the results.arrow_forwardThis is a three-part problem. Two sets of students are collecting traffic data at two roadway stations, station 130 + 00 and station 145 +00. Observations at station 130 + 00 show that five vehicles passed that section at intervals of 0, 3, 4, 3, and 5 sec, respectively. If the speeds of the vehicles were 50, 45, 40, 45, and 50 mph respectively. Note: Stationing is fundamental to highway plans. A station is the horizontal measurement along the Construction Survey Line of a project. Distances are measured and points are identified on plans with reference to station numbers. One hundred feet is equivalent to one station. Highway stationing might be compared with a rope having knots at 100-foot intervals. The beginning end of the rope would be 0, the first knot at 100 feet would be Station Number 1 and would be written as 1+00. The second station number would be 2 (which is 200 feet from the beginning) and would be written as 2+00, and so on. Part A. Determine the time mean speed, in mph.…arrow_forward
- Assume you are an observer standing at a point along a three‐lane roadway. All vehicles in lane 1 are traveling at 30 mi/hr, all vehicles in lane 2 are traveling at 45 mi/hr, and all vehicles in lane 3 are traveling at 60 mi/hr. The spacing between vehicles in each lane is 0.5 mile. If you collect spot speed data for all vehicles as they cross your observation point for 2 hours, what will be the time‐mean speed and space‐mean speed for this traffic stream?arrow_forwardDuring measurement in spot speed study, a total of 1000 vehicles were observed. 85 per centile and 15 percentile speeds were obtained as 40 kmph and 10 kmph respectively. Find the number of vehicles moving between speeds of 10 kmph and 40 kmph.arrow_forwardThe average speed of vehicles on an expressway is being studied. a. Suppose observation on 50 vehicles yielded a sample mean of 65 km/hr. Assume that the standard deviation of vehicle speed is known to be 6 km/hr. Determine the two-sided 99% confidence intervals of the mean speed. b. In part (a), how many additional vehicles' speed should be observed such that the mean speed can be estimated to within + 1 km/hr with 99% confidence? C. Suppose John and Mary are assigned to collect data on the speed of vehicles on this expressway. After each person has separately observed 10 vehicles, what is the probability that John's sample mean will exceed Mary's sample mean by 2 km/hr? d. Repeat part (c) if each person has separately observed 100 vehicles instead?arrow_forward
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