Engines in the Valley: Testing a Park Shuttle

Use noise and air data to judge a plan that cuts traffic in a national park.

Answer Key

Monitoring the traffic

Read the passage and Table 1. Then answer questions 1–4.

A Road Trip to Silverfall Valley

1In July, sixth grader Ezekiel Marchand and his mother drove to Silverfall Valley, a national park with granite cliffs and tall waterfalls. The park and its numbers are made up, but they are based on real parks. One road runs up the narrow valley floor. On summer days, about 5,000 cars a day drive it, and the parking lots fill by 9 a.m., so drivers circle the loop looking for spaces. At the visitor center, Ezekiel met Ranger Ingrid Solano, a scientist who studies the park's air and natural sounds.

2Ranger Solano explained that the park monitors two impacts of traffic. Sound stations record all day, and a computer counts the share of minutes from 8 a.m. to 6 p.m. when an engine can be heard. Small tubes clipped to posts soak up nitrogen dioxide (NO₂), a gas in car exhaust that can harm people's lungs and plants. Each tube hangs for the same two weeks in July, then goes to a lab, which reports the amount in parts per billion (ppb). One station stands at a backcountry camp 6 km from any road, where the engine noise heard comes mostly from airplanes passing high overhead.

3The park wants a plan for next summer. The plan must cut the cars on the valley road to 2,500 a day or fewer, leave room for at least 12,000 visitors a day to reach the trailheads, and cost no more than $3 million a year. It also must not add any new pavement, because pavement would cover the valley's meadows.

4After the park chose a plan, the rangers checked its first summer with the same stations. They also kept stations beside Pine Gap Road, a road in another part of the park where nothing changed.

Table 1. Silverfall Valley in July, Before Any Change
Station	Distance from road	Engine heard (% of min.)	NO₂ (ppb)
Roadside overlook	20 m	85	14
Meadow trail	300 m	50	7
Waterfall trail	1 km	30	4
Backcountry camp	6 km	5	2

At the roadside overlook, an engine could be heard during 17 times as large a share of the minutes as at the backcountry camp, and the NO₂ was 7 times as high.

Which statement best describes Table 1?

A. The meadow trail had more NO₂ than the roadside overlook did.
B. Both noise and NO₂ were lower at stations farther from the road.
C. Noise fell with distance from the road, but NO₂ was about the same at each station.
D. NO₂ fell with distance from the road, but noise was about the same at each station.

Why does the park keep a station at the backcountry camp, 6 km from any road?

A. To show the noise and NO₂ found far from roads, for comparison
B. To check whether the airplanes overhead are flying lower than last year
C. To find out how many hikers walk from the road to the camp each day
D. To catch the NO₂ that drifts uphill from the valley road at night

Why does every NO₂ tube hang for the same two weeks in July?

A. So the lab can test the tubes on the same day and finish its reports sooner
B. So the tubes can soak up the most NO₂, since July is the windiest month in the valley
C. So differences between stations come from where they are, not from when they were hung
D. So the waterfall trail tube catches the same amount of NO₂ as the roadside tube

Choosing a plan

Use paragraph 3 and Table 2 to answer questions 5–7.

Table 2. Plans for Next Summer (estimates for the valley road)
Option	Cars per day	Visitors per day	Cost per year	New pavement?
A. Free shuttle; cars park outside	600	15,000	$2.4 million	No
B. Reservations for 2,000 cars a day	2,000	6,000	$0.5 million	No
C. Wider road + meadow parking lot	6,000	18,000	$1.5 million	Yes
D. Speed limit 55 → 40 km/h	5,000	15,000	$0.1 million	No

Cars per day for Option A counts park trucks and the few cars of people staying in the valley; the buses are not counted.

Which option meets all four requirements in paragraph 3?

A. Option B
B. Option D
C. Option A
D. Option C

Option B cuts more cars than the park requires and costs only $0.5 million a year. What is its main drawback?

A. It would add new pavement on top of the valley meadows.
B. It leaves room for 6,000 visitors a day, well under the 12,000 needed.
C. It costs more each year than the park is able to spend.
D. It would raise the noise at the backcountry camp above 5%.

Compared with today's 5,000 cars a day, Option A would cut the cars on the valley road by 88%.

Did the shuttle work?

The park chose Option A. Table 3 compares the July before the shuttle with the first July of the shuttle. Use it and paragraph 4 to answer questions 8–11.

Table 3. July Before and After the Shuttle
Station	Noise before (%)	Noise after (%)	NO₂ before (ppb)	NO₂ after (ppb)
Roadside overlook	85	35	14	6
Meadow trail	50	20	7	3
Backcountry camp	5	5	2	2
Pine Gap roadside	80	82	13	13

Noise = share of minutes from 8 a.m. to 6 p.m. when an engine could be heard. The valley had about 15,000 visitors a day in the July before the shuttle and about 16,000 a day in the first July of the shuttle.

Underline each result that is evidence the shuttle reduced the impact of traffic in the valley.

Engine noise at the roadside overlook dropped from 85% to 35% of the minutes.The valley had about 16,000 visitors a day in the first July of the shuttle.NO₂ on the meadow trail dropped from 7 ppb to 3 ppb.The shuttle buses cost the park about $2.4 million a year to run.Engine noise at the backcountry camp was heard 5% of the minutes both years.

Why is it useful that the readings beside Pine Gap Road barely changed?

A. It shows the Pine Gap stations were broken during the first shuttle summer.
B. It shows the shuttle also cut the traffic on Pine Gap Road by about half.
C. It shows NO₂ from the valley drifted over to Pine Gap after the shuttle began.
D. It suggests the valley drop was not caused by weather or other changes across the park.

10.

The park wants to keep checking whether the shuttle keeps working in the years ahead. Which plan is best?

A. Repeat the same stations and two-week tube dates each July, including Pine Gap.
B. Hang NO₂ tubes once next January, when few cars use the valley road.
C. Ask visitors at the end of each summer whether the valley seemed quieter than before.
D. Count the riders on the shuttle buses each July and stop the noise and air readings.

11.

A park neighbor says, "The shuttle did not work. The backcountry camp readings did not change at all." Do you agree? Write a claim, use at least two pieces of data from Tables 1 and 3 and the passage, and explain your reasoning.

Claim: I disagree. The shuttle did reduce the impact of traffic in the valley; the backcountry camp was not expected to change. Evidence: The backcountry camp is 6 km from any road, and paragraph 2 says the engine noise there comes mostly from airplanes, so its 5% noise and 2 ppb of NO₂ were already the lowest in Table 1 and the shuttle could not lower them. Near the road, the changes were large: noise at the roadside overlook dropped from 85% to 35% of the minutes and NO₂ dropped from 14 ppb to 6 ppb, and on the meadow trail NO₂ dropped from 7 ppb to 3 ppb. These drops happened even though visitors rose from about 15,000 to 16,000 a day, while Pine Gap Road, where nothing changed, stayed at about 80% noise and 13 ppb. Reasoning: The camp is the comparison station, so it shows what the park sounds like with almost no road traffic. Because the valley stations fell toward that level while Pine Gap did not change, the drop most likely came from the shuttle taking cars off the valley road.