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A New (Old) Transportation Option for California: The Turboprop Solution

WINTER, 2011—In  2007 ITS student Megan Smirti Ryerson filled her backpack and went to Europe. Not—like so many young people—to find herself, but to find a research topic. Two months later, she returned to California with the seed of an idea that not only blossomed into a doctoral dissertation but introduces an intriguing new player in transportation options for the California corridor.

Her dissertation, Optimal Intercity Transportation Services with Heterogeneous Demand and Variable Fuel Price, presents a novel analysis of intercity transportation options. For the casual reader with an interest in California’s transportation challenges, however, it boils down to one word: turboprops.

Yes, Ryerson admits, most passengers are not wild about traveling on these slower, lower-flying, propeller-driven aircraft. “In addition to the extra time—about 20 minutes more between Los Angeles and San Francisco—they are bumpy and noisy,” Ryerson said. Cabins are typically smaller and more cramped than jets.

For all these reasons, plus the relatively low cost of jet fuel until recent years, turboprops nearly disappeared like dodo birds, largely replaced in the 1990s by faster, sleeker regional jets for short-haul (under 1,000 miles) travel. In fact, in 2005, a study found that passengers were willing to pay an extra $40 per ticket not to fly in a turboprop.

The influence of fuel prices

But that was before fuel costs began to rise. Aviation fuel prices tripled between 2004 and 2008 before dropping recently to pre-2004 levels. And while fuel costs have been relatively stable recently, nobody believes they will remain so: The Energy Information Agency forecasts jet fuel prices (reported in 2006 dollars) will rise from just over $2 per gallon today to $6 by 2035. Factor in projections for increased population growth in the state, the effects of climate change policy on aviation, the difficulties of expanding airports and adding runways, and turboprops start to look more interesting.

In Europe, Ryerson observed aviation researchers in Germany and at Eurocontrol, Europe’s version of the FAA, preparing for the inclusion of aviation into an emissions trading system.  Back home, she and her adviser, Civil and Environmental Engineering Professor Mark Hansen, pondered how the U.S. might prepare for increasing fuel prices as well as the inevitable environmental policies regulating aviation emissions.

She began to wonder: If turboprops, known for their fuel-efficiency, were added to the mix of jet aircraft for moving passengers up and down the state of California, how would they stack up? As environmental concerns grow and fuel costs rise, how would turboprops compare to other modes, such as high-speed rail?

Flying between Los Angeles and San Francisco a 50-seat regional jet consumes 925 gallons of fuel and a 140-seat narrow body (think Southwest Airlines) uses 1,083 gallons. A 72-seat turboprops burns only 297 gallons.

“High-speed rail has greater travel time than a regional jet or turboprop, but lower operating costs and lower energy consumption,” she explained. “Jet travel has very fast speeds, but higher operating costs and fuel consumption.” Turboprops fall somewhere in between.  So the question is, given the expected increase in fuel price and the establishment of carbon emissions policies, what would the optimum mix of vehicles be? Jets and high-speed rail? Jets alone? Turboprops alone?

Building a model

To find out, Ryerson developed a total logistics cost model of intercity transportation, sensitive to fuel price and incorporating multiple types of vehicles—regional and narrow-bodied jets, turboprops, high-speed rail—as well as mixes of these vehicle types.

In her model she establishes a central planner, a sort of omniscient god of transportation, who balances passenger cost, based on travel time and frequency of flights, with airline operating costs, such as fuel and labor, to determine the most efficient use of vehicles--jet aircraft, turboprops, and high-speed rail.

Cost to passengers doesn't refer to ticket price, but rather to how travelers value their time: a business flyer may value it more highly; a retiree less so. 

“The mix of the three types of vehicles is really the crux of the paper," she explains. "And the reason that the mix is viable is that I consider passenger value of time to be heterogeneous.”

In other words, when you have a varied group of travelers—passengers who value their time differently—there is greater benefit from mixing the vehicles rather than offering only one type.

Short-haul intercity scheduled transportation, she found in her modeling, is uniquely positioned to meet increasing fuel price with vehicle diversity.

“Obviously, we’re not going to change long-haul trips such as New York to California with vehicle diversity. We may utilize jets that are a bit larger and decrease frequency, but we’re not going to start deploying turboprops or high-speed rail or scheduled buses for such long distances."

For travel between the San Francisco Bay and Los Angeles areas, when fuel prices are very low, the jet comes out ahead: the airline operating cost is relatively low compared to passenger cost, which is based on travel time and frequency of flights. But as fuel costs increase, passenger cost is relatively insignificant compared to airline operating costs. Then, high-speed rail and turboprops begin to nose ahead. Finally, at very high fuel costs, high-speed rail performs best-—even factoring in the costs of building the system.

Turboprops and high-speed rail

Given the performance of turboprops in her analysis, Ryerson thinks airlines might want to take another look at them—especially for short-haul markets like the California corridor. Unlike high-speed rail, which requires an infrastructure that will take years to build, turboprops are already here and have been redesigned to improve both their operating range and passengers’ flying experience. Some international low-cost carriers offer all-turboprop fleets.

Not only could turboprops save fuel, they could transport smaller groups of passengers to and from smaller airports in a more timely manner—something Ryerson thinks should be explored in greater depth.

“Imagine if you’re living on the outskirts of the Bay Area,” said Ryerson. “Currently, you have to drive to Oakland or SFO to catch a plane to LAX. What if you could take a smaller turboprop from, say, Sonoma, to LAX and eliminate a jet flight from SFO? We’re not only saving people the time and fuel required to drive to the airport, we’re using more fuel- efficient aircraft and we’re freeing up airport capacity at these major hubs.”

A large international airport like SFO sees its job as connecting passengers to Asia, Europe and the east coast, not using valuable capacity for connecting passengers from the Bay Area to Southern California, she added. 

“We have the airports today and turboprops need very short runways. We could start tomorrow with turboprops. If they don’t work, we could take them out the next day. There are very low fixed costs to this experiment.”

The payoff in reducing greenhouse gas emissions would also be immediate. “We could be saving so much fuel right now with very few changes,” she added.

So why aren’t we? In a word, competition.

Marketplace realities

Fiercely competitive airlines, not transportation planners, decide which types of vehicles to purchase and what routes to fly. The FAA has a limited role in these two important areas that affect fuel usage, explains Ryerson. Passengers feed competition among airlines because they want the flexibility offered by frequent flights.

In fact, frequency of flights is a higher priority than a lower ticket price for passengers, making it a competitive issue for airlines. Hansen and former ITS student, Wenbin Wei, found that airlines can actually improve their market share by increasing frequency rather than by decreasing fares.

But a more diversified transportation system might better serve both airlines and passengers. Airlines are held back from saving fuel because of passengers and competitive realities, but maybe with higher fuel prices those constraints will erode.

We have the airports today and turboprops need very short runways. We could start tomorrow with turboprops. If they don’t work, we could take them out the next day.

"Because passengers value their time differently, maybe we need fuel-efficient turboprops for seniors, students or others who are willing to pay a little less and fly a little longer," she suggested. Think "Lexus lanes" in the sky: some people will pay more to get to their destination faster. 

She also sees a complementary role for high-speed rail, particularly as fuel prices increase, and argues that high-speed rail is uniquely positioned for the 100- to 200-mile trip.

“My favorite example is LAX to San Diego. It’s a 167-mile trip. But people flying from, say, Asia who are heading to San Diego, have to connect at LAX, and carriers like United have to complete their route network. So passengers fly between the two cities. Right now there are 40 flights a day between San Diego and LAX."

Not only would high-speed rail be almost as fast, it would free up 40 spaces, or slots, at the very congested LAX, allowing those slots to be used for large international flights.

In a transportation planner’s perfect world, a more diverse mix of transportation options would serve travelers better while burning less fuel and emitting fewer tons of greenhouse gases.  But absent an omniscient god of transportation to order a more efficient system, Ryerson believes the way to encourage one, as well as to cut fuel use and resulting greenhouse gases, is to increase the aviation fuel tax.

In which case, turboprops could make a comeback.

Ryerson’s dissertation is divided into six chapters. A journal article based on Chapter 2 has been published in Transportation Research Part D: Transport and Environment, and won the Best Paper Award in Finance and Policy from the Eighth USA/Europe Air Traffic Management R&D Seminar in 2009. Chapter 3 received the Best Paper Award in Prospective Studies and Economics, from the Fourth International Conference on Research in Air Transportation in 2010. Additional articles from her thesis work are under review in transportation journals. Her website is here

--Christine Cosgrove

--Photos by Anders Ryerson