In Pennsylvania Railroad Company v. Locomotive Engine Safety Truck Company, the Supreme Court of the United States was asked to decide whether the Locomotive Engine Safety Truck Company had the right to use the tracks of the Pennsylvania Railroad Company. The Locomotive Engine Safety Truck Company had been granted a patent for a device that was designed to be attached to the front of a locomotive engine and used to prevent the engine from derailing. The Pennsylvania Railroad Company argued that the use of the device on their tracks constituted an infringement of their property rights. The Supreme Court held that the Locomotive Engine Safety Truck Company did not have the right to use the tracks of the Pennsylvania Railroad Company without the railroad's permission. The Court reasoned that the railroad had the exclusive right to control the use of its tracks and that the use of the device constituted an interference with that right. The Court also held that the patent granted to the Locomotive Engine Safety Truck Company did not give them the right to use the tracks of the Pennsylvania Railroad Company without the railroad's permission. The Court concluded that the Locomotive Engine Safety Truck Company was not entitled to use the tracks of the Pennsylvania Railroad Company without the railroad's permission.

In Pennsylvania Railroad Company v. Locomotive Engine Safety Truck Company, the Supreme Court was tasked with determining whether a patent for an invention of a locomotive truck should be held valid or invalid. The majority opinion found that the patent in question was not novel and therefore invalid. Justice Field dissented from this decision, arguing that although some elements of the invention had been previously used in other inventions, it still contained new features which made it unique and thus eligible for protection under patent law. He further argued that if these new features were taken away from the invention then its utility would be greatly diminished; as such he concluded that there were sufficient grounds to hold the patent valid despite prior art existing on similar inventions.