This paper presents the design, modeling, lab test and field demonstration of a railroad energy harvester featuring rapid anchorless mounting. By harvesting energy from rail track deflections, the proposed system can be used as an alternative energy source along the trackside of railroads. Compared to the widely electrified passenger rails, most freight rails are still lack of cost-effective access of electricity because of the long haul and remoteness of the geographic location. This paper aims to address two challenges: increase power capacity and ease of installation. A spring preload and reset mechanism is used to eliminate the need of anchoring the harvester into the railroad foundation, allowing the harvester to be installed rapidly without affecting the track substructures. A dynamic model including the AC generator, the mechanical motion rectifier, and the spring preload is created and the design parameters are obtained from numerical simulations. Lab and in-field tests are carried out to verify the model and simulation. In-field test results show 7 W (average)-56 W (peak) electrical power are generated with a freight train traveling at 64 km/h (40 mph) under 5.7 mm deflections. The proposed harvester has the potential to support many track-side electrical devices and serves as an alternative energy source to enhance rail operational safety.