All Aboard! The Future of Railroads, Subways, and Smart Cities

Population

There are several factors impacting the future of cities. More than ever before, major cities across the United States and the world are seeing large population growth. According to the 2013 May issue of Siemens’ como publication, by 2050, 75% of the world’s population will live in cities. This will lead to the evolution of megacities, cities that are home to more than 10 million people. A megacity can be a single metropolitan area or two or more metropolitan areas that unite to create a large mega-region, which reach numbers of 100 million people or more.

An example would be New York City, which is comprised of five boroughs (Manhattan, Brooklyn, the Bronx, Queens, and Staten Island) and will develop into a megacity. At the same time, the cities of Washington, D.C., New York City, and Boston can develop into a mega-region. Another example would be the cities of Hong Kong-Shenhzen-Guangzhou in China. It is expected that by 2050, 50% of the world’s population will have moved into the middle class, according to the United Nations World Population Prospects: The 2010 Revision. Paired with the previous projection that most people will live in or around urban areas, you can expect a large impact to the methods of travel in and out of cities.

Climate Change and Energy

Climate change is greatly impacting our cities. With the rise of global temperatures in recent years, there has been an associated increase in the frequency and intensity of extreme weather. These changes in temperature, storm activity, and sea level will impact the transportation infrastructure, its design, operation, and maintenance, leading to disruptions, damages, and failures in older transportation systems. The National Research Council reported that damages from flooding will force rail and subway lines to be either rebuilt or raised in future expansion projects. Many of our current rail or subway lines are either near shore or below sea level. Future rail systems will have to be built keeping the rising sea levels and climate changes in mind.

Smart Technology and IoT

With the development and increase of IoT, smart solutions are necessary to modernize transportation systems and methods. The International Transport Forum reported that, by 2050, the mobility of the common passenger will increase by 200% to 300%. As the amount of ridership increases, transportation systems will have to track how many riders a day are on the system, what are the high occupancy times, and what deficiencies reduce the overall quality of the system. This is where the world of smart sensors and analytics can help. Machine-to-machine technology will increase efficiency by embedding sensors in objects and systems to automate tasks and capture real-time information for predictive maintenance. Developments in smart robots will be a crucial part to inspect tunnels and bridges in an aging infrastructure. Robots are already being used to repair water pipes and to test load-bearing cables and tethers of bridges and elevators.

Modern Rails: The Second Avenue Subway Project

History

If the future of cities depends greatly on modernizing transportation like new and efficient rails systems, our methods of construction must improve to accelerate the construction process. The Second Avenue Subway Project is an example of how modern engineering in a busy urban environment is handling that task. In New York City, the Second Avenue Subway has been under construction for the last nine years. The ceremonial groundbreaking took place in April 2007. The Second Avenue Subway is being designed by the engineering firm Arup and once Phase 1 is completed (extension of the Q line from 57th Street and 7th Avenue to 96th Street and 2nd Avenue) it will serve approximately 200,000 daily riders, decrease crowding on the Lexington Avenue Line by as much as 13% on weekdays, which is an average 23,500 fewer riders, and reduce travel time to the Upper East Side by 10 minutes or more.

However, the project has been on the books since 1919 when it was first proposed. It has been a long process to develop the new subway system, especially when you consider the speed with which the initial subway was built. The initial plans for the subway system were approved in 1894 and construction began in 1900. In just four years, workers had laid out over nine miles of track across and the first underground line of the subway was opened in 1904. Within the first 30 years of service, the system we know today was established. So why has it taken so long for the Second Avenue Subway to get underway?

There are several factors that play into the delay of the construction. The first major aspect is a constant changing economic landscape. In 1929, the stock market crashed, resulting in the Great Depression. A new plan was developed but was then placed on hold as the United States entered World War II. Between 1972 and 1975, federal funding was granted and construction started in 1972, but the fiscal crisis of 1975 delayed the project even more. It was not until 2004 that the MTA proposed to reopen the Second Avenue Subway project, creating a new underground line from 125th Street to Lower Manhattan.

The delay due to finances introduced other problems that were not around during the initial construction. Safety regulations and construction standards have improved the workplace environment. The workforce that was used during the original construction, which included underage workers, could not be used today. The average number of workers was 4,661 per day and the single-day high was 12,000.

The methods of construction today are also stricter. The most popular method of construction was the cut-and-cover method. Here, workers would dig giant trenches through existing streets to lay down tracks. The soil is supported by vertical walls and a frame is built to support concrete or the metal street decking. The decking allows for part of the street to stay open while construction continues underground. Once the underground rail and station was complete, the workers cover the trench back up. While cut-and-cover is still used to a certain degree, one could not use it for the whole line with the amount of traffic, vehicles, and people that occurs on Second Avenue. Engineers have turned to modern methods of construction beneath the surface that do not interrupt the traffic and pedestrians above.

Modern Construction Methods

The Second Avenue Subway Project consists of four phases. Phase 1 is scheduled to be completed by the end of 2016. Phases 2, 3, and 4 will see extensions north to 125th Street, south to 63rd Street, and finally south to Hanover Square respectively. The cut-and-cover method will be used for many of the stations. For Phase 1, these stations include 72nd Street, 86th Street, and 96th Street. Modern cut-and-cover methods take into consideration the building types, where a mix of high-rise buildings on plies and low-rise masonry buildings on shallow foundations exist. Limitations on building movement, groundwater drawdown, vibration, noise, and underground utilities lead to the support-wall types to rigid designs: slurry walls, secant pile walls, or contiguous pile walls. These walls can be permanent or temporary once they are combined with a secondary cast-in-place concrete wall. Slurry walls are when a soft mud or cement-like fluid mixture is poured into an open trench. They are mainly used on areas of soft earth close to open water. Secant pile walls are formed by constructing intersecting reinforced concrete piles with either steel rebar or steel beams. The centers of the piles are spaced out, but no less than two diameters apart. Contiguous pile walls are piles of concrete that virtually touch each other and the gaps can be grouted to form a watertight retaining wall.

However, the tunnels connecting these stations will be reached by the modern method via a tunnel-boring machine (TBM). The TBM will tunnel from the existing 63rd Street tunnel, which was started back in 1972, and connect the stations together up to 96th Street. A TBM is comprised by the following parts:

Cutters: Cutting tools, made out of alloy steel, are installed on a large circular steel structure known as the cutterhead.

Buckets: Peripheral scoops are designed into the body of the cutterhead.

Main bearing: The cutterhead is connected to a large and high-capacity slewing, which is installed into the bearing housing known as the cutterhead support.

Grippers system: The TBM anchoring system is located approximately 12-15 meters (40-50 feet) behind the front end. The front end is comprised of the cutterhead plus the cutterhead support/main bearing assembly.

Main beam: A long, hollow steel structure which slides through the gripper systems and bridges the distance between the front end and the gripper carrier.

Conveyor: A belt material handling system installed inside the main beam with its tail pulley inside the cutterhead and the head pulley protruding from the back end of the main beam discharging onto a transfer conveyor.

Propel cylinders: The front end is also connected to the gripper system by a set of large hydraulic cylinders.

Rear support legs: The aft end of the main beam is connected to a set of hydraulic legs to support the TBM during the reset cycles.

The TBM operates by the cutterhead rotating via several large variable electrical drive systems all connected to a common ring gear. The gripper system is engaged and the rear support legs are retracted. The rotating cutterhead is pushed into the rock face by the propel cylinders. The propel force is reacted by the gripper system, which is firmly planted into the tunnel side walls by the large gripper cylinder about 12-15 meters behind the tunnel face. The broken rock or muck chips fall to the tunnel floor in front of the cutterhead. The buckets scoop the fallen muck and elevate it to the top where it falls on the conveyor inside the cutterhead through chutes. The TBM conveyor transports the muck through the main beam and discharges into a muck transfer conveyor to be taken out of the tunnel. When the propel cylinders reach the end of their stroke, approximately 1.8-2 meters (6-6.56 feet), the TBM is reset. The propel push and the cutterhead rotation are stopped. The rear support legs are extended. The gripper system is disengaged from the tunnel wall. The propel cylinders are retracted to reset the gripper system. The gripper system is re-engaged with the tunnel wall. The rear section legs are retracted. The TBM is ready for the next boring cycle.

The TBM has modern advancements like a Human Machine Interface, which includes digital monitors, displays, and controls. This allows for adjustments during the drilling process. It uses lasers and feedback sensors for adjustment. Main-beam type TBMs have the best performance in hard competent rock. They have bored in massive rock formations as strong as 350 MPa (50,000 psi) unconfined compressive strength, which are just as hard as good-grade structural steels.

The third method of construction will be mining. This will be reserved for tight spaces that cannot be accessed by the TBM. Under controlled and monitored conditions, explosives will be inserted into small holes that have been drilled out. They will then be detonated sequentially for short intervals, breaking the rock and soil, which will be excavated and removed by backhoes, bulldozers, and a crane suspended clamshell shovel.

Rail Construction Worldwide

Arup is not only the designing the Second Avenue Subway Project, but has several train designs around the world. The High Speed 1 rail, which runs in London; the G:Link or the Gold Coast Light Rail in Queensland, Australia; and the future High Speed 2 rail, which will connect London to the West Midlands are examples of future rails opening cities to their surrounding areas and becoming larger. In the case of the Gold Coast especially, the region is one of the fastest-growing in Australia, with an annual population growth of 2% to 3%. As we extend ourselves into megacities and mega-regions, more efficient rail transportation using the latest network-connected technology will be needed.