P and D entered into a master license agreement which was intended to be a consolidation of various agreements whereby P granted D licenses to maintain and use 'occupations' and 'appurtenances' over, across, along, and under land belonging to P and its affiliated railroads. The license agreement provides that D has the right to request that additional appurtenances be installed in or over P's land and that P is required to grant the request unless P's engineering officer determines that the installation would interfere with rail operations. P refused D's request to cross with fiber optic cable. D requested the PUC to resolve this dispute, and it ruled for D and P appealed.