CLEARWATER — Renovation work will begin next month at St. Pete-Clearwater International Airport, setting off a string of projects intended to keep up with fast-growing passenger traffic.Construction will begin in April on a $9.8 million terminal renovation that will last 15 months. Over the next few years, it will be followed by work on the entrance road, parking lots, taxiway and baggage inspection system.Among the work for the terminal: a bigger waiting area for gates 7 through 10, larger restrooms, expanded security lines and new air-conditioning equipment. The airport will pay for those projects primarily through passenger fees of $4.50 a person, spokeswoman Michele Routh said.The renovations come as St. Pete-Clearwater has logged three years of double-digit passenger growth, reaching 1.6 million last year, records show. Between 2010 and 2015, traffic more than doubled.The growth owes largely to the airport's emergence as a major destination for budget carrier Allegiant Air, which accounts for more than 95 percent of its traffic. By summer, the airline will fly from here to 50 cities.Airport director Tom Jewsbury said he expected the growth to slow from its breakneck pace, although Allegiant has told the airport it intends to keep adding service. The airport plans to start drawing up a new 20-year master plan this fall to update its growth projections, he said."We really have seen a spike in the last three years. So because of that, we really need to do an update to our master plan," Jewsbury said. In the meantime, the airport plans to move forward with more projects, including some targeted at keeping up with rapid growth: • A new, automated system to inspect checked baggage, costing $6 million. The Transportation Security Administration will pick up most of the tab, the airport says, and a designer will be picked this summer.• Redesigned parking lots and roads that will nearly double the number of parking spots and make way for the proposed Gateway Express project. Design will start next month on the project, which by early estimates will cost $12 million. The airport plans to pay for the work with settlement money from the Florida Department of Transportation (the FDOT had forced the airport to build a new entrance because of the Gateway Express project) and will apply for a grant from the department to cover the rest.• Redone taxiways to connect the terminal with the runways. One phase of the taxiway work has already been done, but a second, $10.5 million project will start in September. Funding will come from the state and the Federal Aviation Administration.The airport is also rebuilding the "terminal apron," the concrete area by each gate where planes park. The $5.3 million project will be done in May. The taxiway and terminal apron projects are part of routine maintenance, Routh said.Jewsbury said the airport is paying for the renovation work with grants and fees instead of bonds in part to insulate itself from the risk of declining business, especially as one airline, Allegiant, accounts for the lion's share of its traffic. Allegiant is a relatively small player in the airline industry, and it has been dogged in recent months by emergency landings and maintenance concerns."We're not taking loans or bonding out to go ahead and pay for these projects," Jewsbury said. "This is money that we're using a combination of grants … or money out of our reserves. So we try to do that to try to minimize our level of risk."Contact Thad Moore at [email protected] or (813) 226-3434. Follow @thadmoore.