The battery EMU (BEMU) market is more developed, largely for European regional lines with so little traffic that wiring them may not be economically justified. As such, some American passenger railroads, such as Metra and the MBTA, have expressed interest in battery-powered trains as an alternative to OCS, citing the lower cost of fixed infrastructure and challenges such as clearance. Many railroads around the world have experimented with battery trains and found little savings over traditional electric propulsion. Despite ongoing predictions of large advances, battery propulsion is still a nascent technology that has suffered notable setbacks. Planned battery train deployments in the Netherlands [27], on Long Island [28], and in New Jersey [29] have failed to materialize. BEMUs recently purchased by Liverpool’s Merseyrail have been fraught with mechanical problems [30]. BEMU deployment on high-ridership corridors is inappropriate for several reasons.
First, BEMUs have around a 100% cost premium over conventional EMUs [31]. Because costs increase with frequency and number of cars per set, and because train sets are recurring investments, this would drive up costs relative to conventional OCS methods. Moreover, charging time drastically lengthens the amount of time that trains lay idle, requiring more trains to be purchased for a given service level than with OCS. For this reason, active BEMU plans in Europe and Asia are generally limited to low-frequency lines running no more than three-car trains.
Second, most BEMU projects save little infrastructure capital cost over traditional OCS. To avoid significant charging time as mentioned above, BEMUs nearly invariably require extensive wired track to charge en route. Worse, the substations must supply high power intermittently to charge the batteries, increasing their cost and negative impact on the grid. Most of the recently deployed BEMUs charge partially from preexisting and/or partially extended wire and run through onto unelectrified, lower-ridership segments. For instance, Baden-Württemburg recently chose battery propulsion to extend electrification on its mostly-electrified system and plans to add OCS to some currently unequipped track [32]. This is likewise the MBTA’s current plan, and it requires approximately 30% of the Newburyport/Rockport Line’s full track mileage to be electrified.
Third, battery trains are likely to be slower and less reliable than their EMU counterparts, reducing ticket revenue and mode share. The combination of weather and limited battery service life is likely to introduce significant variability in charging times at endpoints. Furthermore, on a recently debuted BEMU, engineers had to eliminate traction motors from one of four bogies to fit the batteries, cutting power output by 25% [33]. On that train set, the power reduction adds 15 to 20 seconds of runtime per stop.
