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Controls Today’s railroad cars incorporate many safety features. Ladders have rungs
that prevent feet from sliding off. There are grab bars at climbing transition points and
slip-resistant walkways and handrails. Thermally insulated tank cars prevent heat buildup
and explosions from fires in adjacent cars. Cars carrying hazardous materials have inter-
locking couplings. Locomotives have dead-man controls to prevent runaway trains should
an engineer become incapacitated. Cars containing hazardous materials have placards indi-
cating contents and type of hazard. Automatic sensors placed strategically along main lines
detect overheated bearings.
Based on traffic at crossings, more and more grade crossings are being protected by barrier gates and signals. Sensors that detect the speed of a train activate some gates and ensure adequate lead time for gates to close. Major highways avoid grade crossings with underpasses and bridges. Some cities are diverting main line rail traffic from the inner cities where dangerous traffic conflicts exist.
Aviation
The aviation industry in the United States has grown during this century to the point where millions of passengers travel each year by air. Most propeller-driven aircraft have given way to much larger jet-powered aircraft. Airways have grown more crowded. In the past decade, the number of takeoffs and landings has nearly doubled.
Hazards Aircraft must take off and land without incident. Because airspace in some areas is very crowded, sophisticated electronic gear helps fly the aircraft and control traffic in the highways of the air. Aviation hazards have changed with aircraft scale, speed, and altitude. Structural loads are greater, requiring exotic metals, like fiber-reinforced titanium. Structures face expansion and contraction from repeated loading, pressurization and depressurization, and thermal expansion and shrinkage.
A large portion of an aircraft’s takeoff weight is fuel. Leaking fuel tanks and ignition can be disastrous. Icing of wings and loss of lift is still a danger in severe weather. Designing emergency exiting for as many as 450 passengers is a challenge. Detecting and avoiding wind shear, particularly in clear weather, also remains a challenge.
Controls The newest aircraft have on-board computers and instruments for navigation,
flight control and management, fuel management, fire detection and extinguishment, col-
lision avoidance, pressurization control, and many other functions. Some even have the
capability for automated landing. Air traffic control systems are upgraded continually to
handle increased traffic. Without these systems, aviation would not be possible or as safe
as it is.
Federal Aviation Administration regulations set design standards and control air wor-
thiness of the aircraft and its engines. Flight and maintenance logs help ensure that equip-
ment is in good condition. Regulation of pilot training and certification place qualified
crews in charge of flight. Standards for air traffic controllers are essential, too. Airlines
and aviation employee unions set standards for employee qualifications. Strict manage-
ment and enforcement of flight and operation regulations and procedures contribute to avi-
ation safety.
Pipelines
Pipelines transport gases and liquids. Most materials transported by pipeline are fuels,
including natural gas, liquified natural gas, and other petroleum products, although other