The City's Traffic Congestion
A city's transportation department reports that average commute times have increased by 10% over the past five years, from 30 to 33 minutes. To address this, the city plans to add a new lane to a major highway at a cost of $50 million. The department predicts this will reduce commute times by 5%. However, a study by a local university found that adding lanes often leads to induced demand, where more people drive because of the perceived improvement, eventually restoring congestion to previous levels. The city has a population of 1 million, and 60% of commuters drive alone. The city's annual transportation budget is $100 million.
1. What is the expected reduction in average commute time if the lane addition works as predicted, and what is the cost per minute saved per commuter?
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The predicted reduction is 5% of 33 minutes, which is 1.65 minutes. So average commute time would drop to 31.35 minutes. The cost is $50 million. The number of commuters who drive alone is 60% of 1 million = 600,000. Assuming all commuters benefit equally, the cost per minute saved per commuter is $50,000,000 / (1.65 minutes * 600,000 commuters) = $50,000,000 / 990,000 = approximately $50.51 per minute saved per commuter. However, this is a rough calculation and assumes all commuters use the highway, which may not be true. The reasoning shows that the cost per minute saved is high, and the induced demand effect could negate the benefits.
2. How does the concept of induced demand affect the department's prediction?
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Induced demand suggests that the predicted 5% reduction in commute times may be temporary. As more people choose to drive due to the new lane, traffic volume will increase, potentially eroding the time savings. The department's prediction assumes static demand, but if demand increases, the actual reduction could be less than 5% or even zero. Therefore, the $50 million investment might not yield lasting benefits. The department should consider demand management strategies alongside lane expansion.