Have you ever driven along a street where it seems that every traffic light is red when you get there? Some engineers in Dresden, Germany, are looking at ways to improve traffic flow by enabling traffic lights to communicate information about traffic flow with nearby traffic lights. The data in TrafficFlow show results of one experiment that simulated buses moving along a street and recorded the delay time (in seconds) for both a fixed time and a flexible system of lights. The simulation was repeated under both conditions for a total of 24 trials.

(a) What is the explanatory variable? What is the response variable? Is each categorical or quantitative?

(b) Use technology to find the mean and the standard deviation for the delay times under each of the two conditions (Timed and Flexible). Does the flexible system seem to reduce delay time?

(c) The data in TrafficFlow are paired since we have two values, timed and flexible, for each simulation run. For paired data we generally compute the difference for each pair. In this example, the dataset includes a variable called Difference that stores the difference Timed − Flexible for each simulation run. Use technology to find the mean and standard deviation of these differences.

(d) Use technology to draw a boxplot of the differences. Are there any outliers?