1. Spot Speed Study Lab 2 Instructor:
In this lab, we will take field data of the average speed of vehicles passing along local stretches of road. We will use this data to make some statistical calculations regarding traffic flow in the area. We can then evaluate the design of the road and the traffic laws and enforcement in the area.
Autumn Quarter

2. Key Statistics Mode Pace 85th Percentile Speed Speed
Standard Deviation
Instructor:
Some key statistics we will calculate from our raw data are shown here. Mode is the most common value in a set of data. Pace is the speed range in which most of the vehicles are found, which will be discusses shortly. 85th percentile speed is the speed at which 85% of the vehicles are driving less than or equal to. Speed is distance a vehicle travels per unit time. Standard deviation is a statistic used to find the average deviation of a value from the mean value. This will also be discussed shortly.
Autumn Quarter

3. Pace
Instructor:
This frequency distribution curve shows the percent of cars driving at a given speed. This is the same type of plot that will be created from our lab data. A smooth curve is drawn following the data points without actually “connecting all the dots.” The highest point of the curve is the mode, which is most common speed that vehicles were driving. In this case, the mode is 48.8 mph, and about 22 percent of the cars were found driving this speed. The ten mile per hour range where the most cars were found driving in is called the pace. In this case, the pace turned out to be 43.5 to 53.5 mph.
Autumn Quarter

4. Pace
Instructor:
A second type of graph that will be generated from the data is a cumulative frequency distribution curve. This means that at a given point on the curve, that percentage of cars will be driving at that speed or slower. For example, at the 50% mark on the vertical axis, half the cars will be driving at that speed or slower. In this case, that speed is 48.0 mph. The 50% speed also happens to be the median speed of the cars. If we take the pace speed range from the previous plot ( mph) and find the cumulative percent frequency at those points, we can find the percentage of vehicles found in the pace. In this case, by subtracting the two % frequency values, the percentage of vehicles in the pace is found to be 72%. Another piece of data that can be derived from the graph is the 85th percentile speed. The 85th percentile speed usually turns out to be about the speed limit of the road.
Autumn Quarter

5. Standard Deviation Estimated Calculated Instructor:
There are two ways for us to calculate standard deviation, which is the average deviation from the mean. The simple way to estimate standard deviation is to find the 85th percentile speed and the 15th percentile speed, subtract the two and divide the answer by two. This estimation works best for a symmetrical frequency distribution curve. The way to actually calculate standard deviation is to use the other equation, where xbar is the average value, N is the total number of data points, and xi is a data point. So, all the data points are subtracted from the average value in this equation.
Autumn Quarter

6. Recording Data Instructor:
To take data today, we will use a chart similar to this foot sections of road have been marked off. Vehicles passing through the speed zone will be timed, and a mark will be put in the row corresponding to that time. By counting up all the marks, the total number of vehicles driving that speed can be found. The distance of 176 feet is used because a vehicle traveling 60 mph will go that distance in exactly 2.0 seconds.
Autumn Quarter

7. Recording Data - Roles Flagger Timer Recorder Safety Engineer **
Instructor:
There are distinct roles that each team member must perform. The flagger stands at one end of the speed zone and spots cars to be timed. They will then make a signal to the timer for the timer to start recording. The signal they use should also identify which lane the car is in if the road has multiple lanes. The teams can come up with whatever visual signals (such as handwaving) they wish, but they should NOT distract the drivers passing by. The timer’s responsibility is to stand at the other end of the speedzone from the flagger, start the stopwatch when signaled by the flagger, and stop the stopwatch when the vehicle exits the marked speedzone. They should then read out the time to the recorder, who should mark the corresponding data on the chart. The safety engineer is responsible for making sure all team members stay away from traffic, be aware of oncoming vehicles, bicycles, and pedestrians, and help ensure overall safety for all involved. Every few minutes, the team members should switch roles so that all members have experience performing all tasks.
Autumn Quarter

8. Recording Data - Communication
Lane
Car
Timer Ready
Start Timing
Instructor:
The teams should come up with some visual signals to pass along information to the members. They should be able to communicate what car is to be timed, and what lane that car is in. The time shouldl be able to communicate when they are ready to time a new car. Finally, the flagger should be able to tell the timer when to start timing.
Autumn Quarter

9. Spot Speed Check – Team Locations
Woody Hayes
(Teams A-D) B D D B C C A A E F
Instructor:
Here are the team assignments in the speed zones. Teams A,B,C, and D are on Woody Hayes Drive. Teams A and B are on opposite sides of the street on the bridge that passes over Olentangy River Road. Teams E,F,G,H, and I are all on the same side of Olentangy River Road. The markings on to be followed on Olentangy are on both sides of the road, but the teams should all stay on the same side and well away from the road. E F
Olentangy River Road
(Teams E-I) I G I G
Autumn Quarter

10. Safety Issues KEEP ALERT!! Stay off the road Safety is Job #1
Instructor:
Be sure to keep alert. There have been no injuries yet in the lab, but there have been some very close calls. Be sure to stay off the road, and keep a path for any pedestrians and bicyclists. Also, be sure not to distract the drivers.
Autumn Quarter

11. Lab Reports Individual Reports Look at Example on Web Instructor:
Today’s lab results will be written up as individual lab reports. The format and an example report can be found on the web. Be sure to include the result data and statistics described, and answer any questions found in the lab write-up.
Autumn Quarter

12. Questions?
Autumn Quarter