Determine the proportion of trucks recorded in the traffic flow


Due Date: 15th October 2018

Question 1 – Vehicle Speed Analysis In order to obtain an understanding of vehicle speeds on a rural highway, a small sample of speeds were recorded for vehicles travelling in one direction using a hand held radar device. The speed results are summarised in Table 1. Highlighted cells represent truck speeds. Table 1 – Recorded Vehicle Speeds (one-way) – km/h

97 87 90 91 87 78 83 82 67 32 51 93 82 86 61 86 97 79 83 44 71 61 85 54 85 108 50 71 88 94 101 99 92 107 98 99 100 85 87 105 106 103 100 98 90 99 79 99 92 91 84 102 103 68

1. Conduct the following analysis:

a. Plot a frequency histogram of the recorded speeds. You will need to select your speed bins carefully. Comment on the general shape of the histogram.

b. Determine the average and the 85th percentile speed of the sample. Comment on the findings and why these values may be important in the analysis of vehicle speeds for the highway.

c. Determine the proportion of trucks recorded in the traffic flow. Determine the average and 85th percentile speed of the trucks. Comment on the findings compared to the overall data.

d. Calculate the 95th percentile confidence interval for the population average speed for cars (ie. exclude trucks). Discuss your findings.

e. The posted speed limit for the road is 100-km/h. Comment on the findings of the speed sample, and whether the speed limit seems appropriate for the prevailing vehicle speeds.

2. What proportion of all surveyed vehicles were exceeding the speed limit? Discuss the findings in the context of the posted speed limit.

3. A new access road is to be constructed that connects to this road at a T-junction. Based on the above speed data, calculate the Safe Intersection Sight Distance (SISD and Approach Sight Distance (ASD) for this intersection. Austroads SISD table is provided in Appendix A.

4. After carefully measuring the available sight distance at the new access road’s location, you determine that there is 205 metres available. Discuss whether you think this is adequate and why.

Question 1: 15 Marks

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Question 2 – Vehicle Data Collection and Analysis Introduction You are required to collect traffic data on a selected road. You will need to select a site well away (at least 400 metres) from an intersection, traffic signals, pedestrian crossings, or other obstructions to traffic flow. You should select a site where you can easily observe vehicles travelling in one direction (traffic may be in more than one lane, but all traffic must be travelling in one direction). A reasonable traffic volume is required, ideally in the range of 200 to 300 vehicles per hour. Do not select a high volume road that exceeds 600 vehicles per hour as the random arrival model breaks down beyond this range. Safety As you will be required to collect data from a roadside, it is essential that you exercise care when in the field. You must act lawfully at all times and you should observe traffic from a safe position off the roadway. You should be able to collect data during daylight hours. Be aware of your own personal security/ safety in the area where you are collecting your data. Data Collection The following data needs to be collected at the site:

1. Head ways. Record the times at which 61 consecutive vehicles, travelling in the same direction, pass a point beside the road. Measure the event time to the nearest second.

2. Vehicle Counts. Count the number of vehicles passing the point beside the road in each 10 second interval for 15 minutes.

Data Processing

1. Headways. Enter the times at which the 61 consecutive vehicles passed the point beside the road into a spreadsheet. In the spreadsheet determine the headway between vehicle arrivals \. Then plot three histograms – one using a one-second time interval, one with a two-second interval, and one with a five-second interval. In the case of the one-second interval, the histograms should show the number of headways between 0 and 1 second, 1 and 2 seconds, 2 and 3 seconds, etc.

2. Vehicle Counts. Produce a histogram of ten-second counts. The X-axis should show the number of cars observed in a 10 second interval (0,1,2,3,4, etc) and the Y-axis should show the number of the 10 second intervals within which that number of cars were observed.

Data Analysis You will now need to interpret the data. You will need to ensure that you provide enough details of your calculations to enable them to be checked.

1. Headways. Find the proportion of headways exceeding 5 seconds and the proportion exceeding 8 seconds. Compare these proportions with the theoretical proportions predicted by the random traffic model using the following mean flow rate:

q = 60/(t61 – t1) where ti is the arrival time of the ith vehicle, and q is the traffic flow in vehicles per second.

2. Vehicle Counts.  Compare the observed frequencies for the 10 second counts with the theoretical

frequencies for the Poisson Distribution.

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 Aggregate the 10 second counts to produce counts for 20 second, 30 second and 60 second intervals.

 Calculate the ratio of the variance of the vehicle counts to the mean vehicle count for the 10, 20, 30 and 60 second counts. What should that ratio be if the data is consistent with a Poisson Distribution? Do your results suggest that ta Poisson model would represent your data?

Question 2: 35 Marks

Question 3 – Road Safety Engineering Crash data was obtained for an urban, low speed T-Junction for a five-year period to August 2018. The T junction has the major road connecting east-west and the minor road connecting to the south. The ‘Definitions for Classifying Accidents’ (DCA Codes) are provided in Appendix A. Crash The crash data for the intersection is summarised in Table 2. Table 2 Crash Data

Date Time Approach Severity Crash Type

Weather Road Surface

18-Dec- 14

7:18am West Property Damage

130 Clear Dry

9-Jul-15 8:38am South Property Damage

113 Clear Dry

18-Jul-15 5:08pm South Minor Injury 111 Clear Dry 12-Aug-

16 2:44pm East Minor Injury 121 Clear Dry

22-Aug- 16

10:42pm East Serious Injury 100 Clear Dry

21-Dec- 16

9:07am West Property Damage

132 Rain Wet

27-Aug- 17

9:31am East Property Damage

121 Clear Wet

22-Nov- 17

8:22am West Property Damage

130 Clear Wet

4-Jul-18 5:53pm South Minor Injury 111 Clear Dry Using the crash data in Table 2, undertake the following:

a. Construct a collision diagram for the intersection b. Describe any crash trends that may be evident for the intersection. c. Determine two potential countermeasure treatments that may reduce the crash trends

(refer to Appendix C for countermeasure effectiveness of various treatments)

Question 3: 15 Marks

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Question 4 – Traffic Generation A small shopping centre is to be constructed on the fringes of a large residential area. The shopping centre consists of the following key components:

 K-Mart 5,500m2  Supermarket 2,400m2  Specialty stores 1,800m2 (10 x 180m2 shops)  Offices 340m2

Using the traffic generation rates from the RMS publication ‘Guide to Traffic Generating Developments’ provided in Appendix B, calculate the traffic generation as follows:

1. The weekday (Thursday) daily traffic generation of the shopping centre 2. Thursday evening peak hour generation 3. Friday evening peak hour generation 4. Weekend (Saturday) peak generation

Question 4: 10 Marks

Question 5 – Unsignalised Intersection Analysis The shopping centre in Question 4 will be accessed by 3 main accesses. The primary access will be the southern approach on a major 2 lane, 2-way road. The access has one exit lane and one entry lane. It is estimated that 70% of all traffic generated by the site will utilise this access. Of this traffic, 70% will originate and terminate to the west of the access (as this is the direction that the higher proportion of residential catchment area is located). You may assume that the traffic generation consists of 50% inward and 50% outward traffic for all analysis periods. The frontage road has an AADT of 9,500 vehicles per day, with an evening peak of 1,420 vehicles per hour. During the evening peak, 80% of traffic on the main road travels west. During the morning peak, 40% of traffic on the main road travels west. The frontage road carries 12% heavy vehicle traffic. Calculate the following:

a. The turning movements at the shopping centre access during the Thursday evening peak period.

b. The AM and PM peak capacity of the shopping centre approach. You may assume critical gap and follow up gaps of 5 & 3 seconds for the right turn manoeuvre and 4 & 2 seconds for the left turn manoeuvre.

c. Calculate the Level of Service of the shopping centre approach using the HCM Delay methodology (provided below) for the weekday evening peak period.

d. Calculate the average queue and 85th percentile queue for the shopping centre approach. e. Calculate the average delay and 90th percentile queue for the right turn entry movement

into the shopping centre (western approach).

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f. A right turn lane is proposed for the western approach to improve efficiency and safety on the main frontage road. The right turn lane can accommodate 2 cars. What is the probability that 2 cars will be exceeded during the weekday evening peak period.

HCM Level of Service (delay method)

Question 5: 20 Marks

Question 6 – Signalised Intersection Analysis The shopping centre junction in Question 4 has been in operation for five years. During this time, traffic flow on the main frontage road has increased at a rate of 4% per annum, and the shopping centre has expanded, resulting in an overall 12% increase in traffic generation. Due to a high incidence of angle and rear-end collisions at the site, the road authority is converting the intersection to a signalised junction. The design of the junction will include the following:

 2 lanes on each approach. These lanes include a dedicated through lane and a dedicated turn lane on the main road approaches and dedicated left and right turn lanes on the shopping centre approach.

 The right turn entry movement (into the shopping centre) must be an un-opposed movement due to the poor safety history and high demand.

 There is a high demand for pedestrians on the western crossing of the main road. Pedestrian phasing must be included on this approach as well as across the shopping centre approach.

 You can assume lost time and Intergreen time of 4 seconds on each approach.  Minimum displayed green time is 8 seconds for vehicular phases and 15 seconds for

pedestrian phases. Determine:

1. The new turning movements at the junction. 2. The most appropriate phasing of the junction 3. The critical movements 4. The green time for each movement 5. Calculate the optimal cycle time for the intersection (C0)

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In your answer assume that the intergreen time and lost time are each 4 seconds, and the minimum displayed green time and minimum effective green times are 7 seconds. The practical degree of saturation can be assumed to be 0.9. State all assumptions used in your analysis.

Question 6: 20 Marks

Question 7 – Traffic Modelling Analysis The road network in a particular commuting corridor can be represented in terms of five links and four nodes as shown in the Figure below.

Link service functions for each of the links are as follows: t1 = 9 + 0.013 V1 t2 = 8 + 0.015 V2 t3 = 26 + 0.011 V3 t4 = 6 + 0.009 V4 t5 = 12 + 0.005 V5 Where ti is the travel time and Vi is the volume on Link i. A total of 55,000 vehicles are traveling from Node A to node D.

a. Predict the volume and travel time on each link using the All-or-nothing assignment technique (AON).

b. Predict the volume and travel time on each link using an incremental assignment algorithm with eight 12.5% increments.

c. Comment on whether your answers in (a) and (b) represent true user equilibrium flow for the network.

Question 7: 15 Marks

TOTAL MARKS: 130 Marks

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APPENDIX A Austroads Sight Distance Requirements – (Austroads Guide to Road Design, Part 4A: Unsignalised and Signalised Intersections, 2009)

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APPENDIX B Shopping Centre Traffic Generation Rates (RMS NSW, 2002)

Daily Generation:

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Appendix C Definitions for Classifying Accidents (DCA Codes)

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