The EP-4s were The New Haven's second series of 2-C+C-2 passenger electrics. Arriving in 1938, they had a modern style for the time. While some may believe the design was influenced by the GG1, which was unveiled four years earlier. In fact, the design of the EP-4 and the GG1 were influenced by the NH locomotive's predecessor, the EP-3, which shared the wheel arrangement of the later classes, but had a box-like body.

The EP-4 could operate into Grand Central, over the NYC, by the use of third rail pickups, and a small third pantograph that collected DC current from overhead contacts, in sections of the Park Avenue tunnel, where track work made installation of third rail difficult. They could run on either AC or DC because of their series-wound "universal" motors. This type of motor can only "digest" low frequency AC, so the railroad had to produce its own power, 11,000 volts, 25hz AC, at a plant in Cos Cobb CT. Only when UM powered equipment was retired from the former NH and PRR electric zones (after the introduction of rectifier locomotives) was the railroad able to switch over to 60hz commercial power.

The EP-4s were retired after a fairly short period, by the inept management that followed the quirky but competent administration of Patrick McGinnis, in the late 50s. 20 years of service is nothing for an electric locomotive.

ALCo was New Haven's favorite locomotive builder, both in the steam and diesel eras. Therefore, it's not surprising that PAs formed the bulk of NHs passenger fleet from the late '40s to the early '60s, when EMD FL9s quickly replaced them.

In 1934, New Haven took delivery of the first of what would become one of the most distinctive and recognizable passenger car fleets in the nation. These first examples of this type were 80-seat coaches, designed for medium distance trains, like the Boston - NYC runs that were the core of New Haven's intercity passenger business.

These cars were immortalized in 1946, when A. C. Gilbert (who had previously invented the Erector Set, based on the construction of the catenary towers in NH's electrified zone) offered the first S-gauge American Flyer model train sets. The line of equipment included a 3/16" scale model of the 8200 series New Haven lightweight coach. These models became so recognizable that the prototype cars themselves became known as "American Flyer" cars

When delivered, these cars were painted a dark shade of green, known as "Forest Green", with the aluminum window frames unpainted. In the '50s, New Haven changed passenger paint colors several times. The last green scheme used a color known as "Hunter" green. In this scheme, the window frames were painted the same color as the car side, but the roof was black.

The second group of lightweight coaches were configured with 92 seats, vs 80 in the Deluxe coaches. They had 11 windows per side, instead of the earlier cars' 10. These cars were intended for short distance commuter trains, while the Deluxe coaches ran in long range intercity trains.

These "Grill" diners served "fast food" to passengers on New Haven's local trains. They also had the distinction of being the first railroad diners partially crewed by women, as table service was provided by uniformed waitresses.