Argyropolis' subway platforms were built to accommodate eight-car trains, but no trains longer than six xars have ever been used. Subway overcrowding has recently prompted officials to propose using eight-car trains, but for the platforms to accommodate such trains, the trains must be stopped with a degree of precision that train drivers cannot reliably achieve now nor be retrained to achieve. Therefore, overcrowding cannot be eliminated simply by using longer trains, given that ________.