The article"Modeling Arterial Signal Optimization with Enhanced Cell Transmission Formulations" (Z. Li, Journal of Transportation Engineering 2011:445 – 454) presents a new method for timing traffic signals in heavily traveled intersections. The effectiveness of the new method was evaluated in a simulation study. In 50 simulations, the mean improvement in traffic flow in a particular intersection was 654.1 vehicles per hour, with a standard deviation of 311.7 vehicles per hour. a) Find a 95% confidence interval for the improvement in traffic flow due to the new system. b) Find a 98% confidence interval for the improvement in traffic flow due to the new system. c) A traffic engineer states that the mean improvement is between 581.6 and 726.6 vehicles per hour. With what level of confidence can this statement be made?