More than two million Muslims travel to Mecca each year to participate in the annual Hajj, or pilgrimage, which takes place over six days. To improve traffic movement, the Saudi government will build an 18-kilometer-long monorail system linking the pilgrimage sites. Trains on four elevated tracks will carry up to 20,000 pilgrims per hour, transporting as many as 500,000 pilgrims every six to eight hours. According to a report issued by the Supreme Hajj Committee, once the monorail is operating it will allow for removal of 53,000 buses and other vehicles. The monorail is being built by China Railway Construction
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.