Nearly 40 million Americans will kick off one of the busiest travel seasons in history this Memorial Day weekend, jarred by potholes on America’s roads, crossing her aging bridges, riding her antiquated railways and taking off from airports that draw international scorn. Long a source of national pride, America’s infrastructure is in critical need of repair, but federal government spending on the issue has gone down 9% in the past decade. As former Secretary of Transportation Ray LaHood says, “We’re like a third-world country when it comes to infrastructure.” CNN aviation and regulation correspondent Rene Marsh investigates the state of the country’s bridges, railways, airports and pipelines in a four-part series: America’s Crumbling Infrastructure. Check back here from now through Monday. Part 4: Damaged pipelines and a “ticking time bomb” The government says strung together they would run more than 90,000 miles. High-risk pipelines carrying essential but dangerous fuels like natural gas run under the streets and buildings of dozens of major American cities. And when they go bust, the results can be deadly. Eight-year-old Troy Douglas was killed walking home from school when an explosion rocked his Baltimore neighborhood in 2014. The pipelines in the vicinity of the disaster ranged from 84 to 106 years old, some of them cracked and corroded. Baltimore Gas and Electric, the utility company responsible for the piping, was unable to determine the cause of the blast. State investigators blamed a natural gas leak. Investigators found a cracked and corroded six-inch line planted during the Great Depression in the area of the explosion. Records show the same pipe had been repaired twice in the previous months leading up to the explosion. “It just didn’t need to happen,” said Mark McDonald, a natural gas expert who investigated the explosion on behalf of the family. “It was a ticking time bomb.” The utility company settled with the Douglas family for an undisclosed amount. Still, the utility company told CNN, the old pipeline that runs adjacent to the exploded building has not been replaced, only patched. Between 2006 and 2015, incidents similar to the one in Baltimore have killed an average of 13 people annually. Fifty-nine are injured every year, according to the Pipeline and Hazardous Materials Safety Administration. The Federal agency is the division of the U.S. Department of Transportation responsible for federal oversight of these pipelines. The natural gas industry says it is actively replacing aging pipelines, but the rate of replacement depends on dollars available. The pipelines belong to the energy companies, who are responsible for paying the cost of repair and replacements – expenses that are ultimately passed onto consumers. The industry says there are caps on how much it can raise customer rates to fund its aging pipeline replacement program. A Department of Energy report estimates it would cost $270 billion to replace all of the aging pipelines. Transportation Secretary Anthony Foxx, whose department is tasked with overseeing pipeline safety regulations, told CNN standards are improving and enforcement has ramped up. “We are putting in place the regime to ensure that we will not only be a leader in energy production, but a leader in safe energy production, and these efforts are underway,” he said. But of the 42 requirements Congress mandated for pipeline safety in 2011, only 26 have been completed by the Pipeline and Hazardous Materials Safety, a division of the Department of Transportation. Administration a division of DOT, has only completed 26 of the requirements, according to a written statement from the federal regulator to Congress. One recent addition puts a new focus on dangerous, aging pipes. The rule took five years to get in place. DOT tells CNN it will continue to develop stricter regulations for the natural gas industry but government red tape makes it a slow process. Part 3: Funding delays ground flights and cancel commercial ambition Commercial air travel in America is primed for a summer surge. More than 230 million passengers are expected to fly in the coming months. But packed flights also mean long security lines, delayed departures, missed connections and more frustrated passengers than ever before. Outdated and overcrowded airports are in dire need of upgrades. Once at the forefront of aviation innovation, U.S. flight hubs in the 21st century are falling far behind their international competitors. “People are going through airports built in the 1950s, the 1960s, the 1970s,” says Kevin Burke, president and CEO of Airports Council International. That infrastructure, largely unchanged for decades, is struggling now to service a nearly 12-fold spike in passenger volume across the decades. Traveler frustration has made for some rare common cause among quarreling presidential candidates and political leaders. “Our airports are, like, third world,” Donald Trump said in February. Vice President Joe Biden used the same term to describe New York’s LaGuardia Airport after a 2014 visit. On the campaign trail in January, Hillary Clinton said she was upset “that we don’t have a single airport in our country that is considered in the top 25 in the world.” Doug Parker, the CEO of American Airlines, says the rhetoric doesn’t match the reality. “If you go to any airline check-in counter today, you won’t see long lines,” he tells CNN. “We made huge investments in making it much easier for customers to get from – you know, from their cars to the airplane without waiting in long lines other than TSA. But that’s not an infrastructure issue.” But for many frequent fliers, it’s hard to tell where one hold-up ends and the next backlog begins. In Kansas City, its airport has ranked among the nations worst. New York and Los Angeles have earned a spot on the worst airports list in the past as well, mainly because of outdated terminals that cannot meet passenger capacity demand. “We have gates that don’t accommodate the A380, or expanded 747, or some of the modern aircraft that will be there,” Burke says. “Somebody has to pay for that. In order to accommodate new aircraft, you have to adjust the airport. You have to adjust the taxiways.” New money is on the way for some airports, but a varied funding mechanism — the airlines, along with the federal, state and local governments, all chip in — often complicate the matter. The federal tax used to pay for airport construction projects, usually baked into passenger airfare, hasn’t been adjusted for inflation in 16 years. The simpler, more robust systems powering global hubs show just how far the U.S. lags behind. South Korea’s Incheon International, located about 90 minutes outside Seoul, consistently ranks as one of the best in the world. With showers, spas and an on-site hotel, travelers can enjoy a concert while shopping at high-end retail stores. The Airport Council International says Congress would need to invest an estimated $75 billion over the next five years to begin to compete with the government-subsidized gems in Asia and the Middle East. “It’s not a fair fight,” Burke says. “Their governments recognize the importance of airports. Our government says it does, but they need to show it by increasing funding for us.” Parker also points to the need for upgrades to the Federal Aviation Administration’s air traffic control system. Created in the 1960s, during the first flight boom, the technology hasn’t quite kept up with the times. Upgrading to real-time GPS locators that could unsnag air traffic and speed up arrivals. “It takes longer to fly from Point A to Point B in the United States than it should,” Parker says. For an industry that brings in about $1.6 trillion annually for the American economy, every second counts. Part 2: The busiest rails shut down by failing power cables The Portal Bridge in New Jersey is the most heavily trafficked rail span in the Western Hemisphere. Connecting New Jersey to New York City’s Penn Station, an estimated 450 trains cross it every 24 hours. Below – sometimes not much more than 25 feet down – is the Hackensack River, itself a busy thoroughfare for boats and barges. To accommodate both, the Portal Bridge operates on a swing-span, allowing it to open for watercraft, then close up again to complete the rail path. “The problem we have is that, as it swings back, those miters don’t always come down right, because this thing is so old,” explains Amtrak CEO Joe Boardman. And when those “miters” don’t line up correctly, train traffic grinds to a halt. “So then you have to get crews out here,” Boardman says. “That holds up a lot of trains, no matter what time of the day it is.” The Portal Bridge, like so much of America’s archaic and often wonky infrastructure, was designed in the 19th century and built more than a hundred years ago. But funding for the construction of a new passage is finally forthcoming – and the project to replace the rails is underway. Less than nine miles east, the tunnel that connects Jersey City to Manhattan is cracked and crumbling. The 106-year-old Hudson River Tunnel connects more than 230,000 commuters daily, but in the aftermath of Superstorm Sandy in 2012 it has been plagued by power failures, causing shutdowns and days-long delays. “This salt is eating away at the concrete, it’s eating away at the rails, it’s eating away at the cables that go through here for power,” says Boardman, who describes it as one of the most disturbing examples of an infrastructure system long ignored or deprived of needed maintenance. The price of renewing and safeguarding the web of railways that runs up Amtrak’s “Northeast Corridor” – more than 450 miles – stands at an estimated $20 billion. The cost for passengers has been steeper. In May 2015, an Amtrak passenger train traveling more than twice the 50 mile per hour speed limit jumped the tracks in Philadelphia. Eight people were killed and more than 200 riders were injured. The deadly derailment might have been prevented if the tracks had been fitted with a technology called “Positive Train Control,” an innovation that automatically slows speeding rail traffic. So what’s taking so long? “It takes time to make sure it works right,” Boardman says. Across the country, 30 freight and passenger train accidents, 69 deaths, and more than 1,200 injuries could have been prevented had the technology been in place, according to the NTSB. With Congress tied up in partisan knots over new spending, the bullet trains of Japan – which cruise at nearly 200 miles per hour and could cut in half the travel time between Boston and Washington, D.C. – seem a long way off. Implementing a similar system along the northeast corridor would come with a price tag exceeding $151 billion. “You want to be able to show the benefit of the dollar you invested,” Transportation Department head Anthony Foxx tells CNN. “I think members of Congress struggle, because (these projects) actually require longer than a political term to take root.” Short term thinking leads to long term trouble, and for the busiest strip of track in the Americas, the crumbling is becoming more difficult – and dangerous – to ignore. Part 1: Bridges supported by crumbling 90-year-old beams Nearly 60,000 bridges across the country are in desperate need of repair. One example is just down the street from the White House and Capitol Hill. In the nation’s capital, 68,000 vehicles cross the Arlington Memorial Bridge between Washington and Virginia every day. CNN was granted rare access to go inside the crumbling bridge. “It’s just eroding and concrete is falling off,” said National Park Service spokeswoman Jenny Anzelmo-Sarles as she showed how the original support beams from 1932 are corroding. The beams have never been replaced, and the bridge could be closed to vehicle traffic within five years if it isn’t fixed. It’ll cost $250 million. In 1932, as the Arlington Memorial Bridge was being erected, Congress was dealing with the Great Depression. That same year, President Herbert Hoover enacted the first federal gas tax at 1 cent per gallon. The gas tax is a major source of funding for bridges and roads that has been raised periodically until 1993, when it was set at 18.4 cents per gallon. Although the gas tax has remained steady, cars have become more efficient and overall federal government spending on infrastructure has declined 9% from 2003-14, according to the Congressional Budget Office. According to the American Road and Transportation Builders Association, every state has some degree of bad bridges that need to be repaired. In Los Angeles, CNN found trees growing out of cracks in a bridge. In Chicago, netting is in place to protect drivers from falling concrete. LaHood was a rare Republican who served in President Barack Obama’s administration. He says there’s an easy way to fund upgrades to an infrastructure system that has become “third-world”: Raise the gas tax. LaHood and others blame Congress for failing to raise the gas tax in 23 years. Republican Rep. Bill Shuster, who chairs the House Transportation and Infrastructure Committee, said raising the gas tax “doesn’t solve the long-term funding problem.” But Congress has not yet come up with a solution. Beyond funding, there is another issue: how to make the bridges better. Researchers at the University of Michigan believe they may have a fix: bendable concrete that can heal itself from cracks. Demonstration in the university’s engineer lab shows regular concrete can fail quickly and suddenly. Professor Victor Li, who developed the technology over the past 10 years, said the bendable concrete can withstand a force hundreds of times more powerful than standard concrete. The researchers’ hope is that it could help already crumbling bridges, like the Memorial Bridge near the nation’s capital. But new concrete is expensive. According to the American Society of Civil Engineers, bridge infrastructure investment needs to be increased by $8 billion annually. The society said that increase would address the estimated $76 billion in needs for deficient bridges across the United States.