This Alco/GE built electric locomotive from 1923 and the electrification was to enable better performance on the steeply graded (up to 4.7% between Esparanza, Puebla and Paso del Macho it is stated) line from the Gulf Coast at Veracruz over the Cumbres de Maltrata to the Central Plateau at around 2,500 metres altitude.
The 10 boxcab locos ran on 3000 Volts DC from overhead catenary.They were equipped with regenerative braking -- when going downhill the traction motors generated power to feed back into the catenary that could be used to power ascending locomotives. Returning much of the power used to climb the grade reduced the cost of operation and allowed for a smaller central power plant.
These electric locomotives drastically reduced cost and time. While 2 steam locomotives were required to climb a 4.7% grade at 12 km/h pulling 300 tons, 2 electric locomotives could pull 600 tonnes at 25 km/h - more than 4 times the tonne-miles per hour.
Type: Bo+Bo+Bo -- 3 trucks (bogies) with 2 motorized axles each
Maximum output power: 2,736 horsepower
Weight: 150 tonnes
Length: 16.12 meters
The Veracruz via Orizaba route, extensively upgraded, is still heavily used for freight traffic, but now diesel-operated. At least one of the boxcab electrics is preserved, unit 1001, at the Mexican national railway museum in Puebla.