CE361 Introduction to Transportation Engineering



CE361 Introduction to Transportation Engineering |Out: Monday 29 August 2005 | |

|Comments on Project 1 = 2 HWs = HW 2 |Due: Friday 9 September 2005 |

TRAFFIC DATA COLLECTION AND ANALYSIS – FLOW, SPEED, AND DENSITY

1. Vehicle flow and classification.

A. (10 points) Vehicle classes. Create a worksheet with 31 rows (one for each 20-second interval plus totals in each class) and 15 columns (14 vehicle classes plus total vehicles) to summarize your vehicle classification data. A “worksheet” is one “layer” of a spreadsheet or workbook file.

B. (10 points) Vehicle flow rates. Using a new 16th column in the worksheet for Part 1A, convert your 20-second vehicle counts into vehicles/hour flow rates. Show one sample calculation by hand.

(3 vehs/20 sec.)*(3600 sec/hr) = 540 vehs/hr

2. (10 points) Traffic density. Convert your 20-second counts into density values. Explain how you did this and show one sample calculation by hand. At this point in your report, state where each member of your group was located when collecting his/her data.

A common mistake here was to use the flow rate as the vehicle count. You were supposed to “count the number of SEB vehicles that are located between the two crosswalks” at the start of each 20-second interval. Distance between the crosswalks was estimated by pacing (296-354 ft), measured with a steel tape (350-351.5 feet), or timing a vehicle driven at a constant speed (312-354 ft). Four groups did not explain their procedure. Density (vpmpl) = (vehs/2 lanes)/dist.

3. Vehicle speeds.

A. (10 points) Explain how you converted travel time for a vehicle you observed into its speed from Crosswalk 1 to Crosswalk 2. Show one sample calculation.

Speed = dist/time = (354 ft/8.8 sec) / (1.47 fps/mph) = 27.3 mph

B. (15 points) Create Worksheet 2 in the same workbook/spreadsheet that was created for Problem 1A. It should have columns for Time Interval, Travel Time (sec.), and Speed (mph), and a row for each vehicle. In this worksheet, carry out your calculations of vehicle speeds for all vehicles you timed during the ten minutes.

4. Data summary.

A. (10 points) Table 2.9 facsimile. Using the data produced in Problems 1-4 above, create a Worksheet 3 with 33 rows that looks like FTE Table 2.9, except that the “Occupancy” column can be omitted and the “Density” column will have values. Row 1 will contain the title of the Worksheet. Row 2 will contain the names of the team members. Row 3 will contain the date and time at which the data collection began. Rows 4-33 will contain the 20-second data.

Things you should have explained: How did you calculate average speed with for 20-second interval? To which interval did you assign a vehicle that was between the crosswalks for more than one interval?

B. (15 points) Data plots. On Worksheet 4, plot the 30 data points in an attempt to replicate FTE Figures 2.21-2.23. Do the plotted points resemble any portion of any of those figures? If they do not, explain why they don’t. Email the completed workbook/spreadsheet file to rmelshei@purdue.edu.

A common error: If a 20-second period had no density or flow, it could not have a speed for that period. Nevertheless, many points were plotted along axes in the three plots. This contaminates any attempt to fit a line to the speed-density data, for example. Because such points have no physical meaning, remove them from a plot that is the basis for a line/curve fit.

5. Full-scale data collection. Given your experience in this project and the techniques and technologies described in FTE Chapter 2, …

A. (5 points) How would you improve the preliminary project?

Make the time interval a little longer than 20 seconds (30 seconds? One minute?) to increase vehicles observed in7 each interval. Assign groups to time intervals that increase the range of data values observed. Use radar gun, video camera, temporary sensors such as rubber treadles or pneumatic tubes. Pick a location without a potential turnoff (such as the parking garage entrance) between checkpoints.

One student asked me, so I found out: The loops that appear in the “Closeup of Crosswalk 2” figure below are actually “temporary” tape loops that were installed years ago. Although they are still in place, the wires they contain have been damaged. Normally, tape loops do not last long, but they may be useful for the preliminary study.

B. (15 points) Design a data collection effort that you would recommend to use if your firm were awarded a contract to do a full-scale study to create a version of FTE Table 2.9 that includes every SEB vehicle for a 24-hour period. Although cost would be a factor, place your emphasis on accuracy and efficient use of personnel. What are the pros and cons involved in using higher-level technology than you used in this preliminary study?

Higher technology, such as inductive loops or video cameras, offer greater accuracy. Their higher costs may be offset by savings in personnel needed for the project. Video tape will provide a “second chance” at observing vehicles, to check for missed vehicles, incorrect measurements, or issues that arise later. However, video cameras may not be useful in hours of darkness and some technologies can malfunction. The level of training for personnel may raise costs.

|[pic] |[pic] |

|Crosswalk 2 |Crosswalk 1 |

|[pic] |[pic] |

|Closeup of Crosswalk 2 |Closeup of Crosswalk 1 |

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