This paper designs an electromagnetic vibration energy harvester based on twin ball screws (EH-TBS) to power wireless sensors and auxiliary equipment along heavy-duty freight railways. Bidirectional vibrations of the track are efficiently transformed into unidirectional rotational for the generator by utilizing twin ball screws and spur gears with integrated one-way bearings. This design effectively mitigates the issue of backlash in the gear transmission. A full-scale prototype of the EH-TBS is constructed, and laboratory tests are conducted using harmonic displacement excitations with varying amplitudes and frequencies to simulate different train speeds and load conditions. Results demonstrate that the output voltage of the EH-TBS is directly proportional to the amplitude and frequency of the input excitation. Under the harmonic excitation (4 mm, 2 Hz), the EH-TBS achieves a peak phase power of 9.02 W and an average three-phase power of 6.52 W with external loads of 1 Ω. The charging tests confirm that the EH-TBS has significant application potential as a sustainable power solution for powering intelligent rail transit sensors.