Photo courtesy Mike Shahan and North Texas Regional Airport Replaceable? Some small airports can afford manned control towers, such as North Texas Regional Airport, shown here. Related Links: More ENR Information Technology News NextGen Ramps Up Amid Flat Airport Improvement Funding Air Traffic Is Reviving and Construction Is Back To Basics Deterred by the $2-million cost of constructing an air traffic control tower and the $400,000 annual cost to operate and maintain it, managers of the Raleigh County Memorial Airport in Beckley, W.Va., are considering the installation of the first unmanned, virtual control tower as an alternative."This would answer all
Arch dams, classically curved monoliths situated in narrow valleys, are not as common as other types of dams, such as embankment dams and gravity dams. ENR takes a look at some of the biggest arch dams in the world, both completed and under construction.