It uses a Marsh rack system and both steam and biodiesel-powered locomotives to carry tourists to the top of the mountain.

Local tradition says that the state legislature voted permission based on a consensus that harm resulting from operating it was no issue – since the design was attempting the impossible – but benefits were guaranteed.

[7] Marsh obtained a charter for the road on June 25, 1858, but the American Civil War prevented any action until May 1866.

[5][8] He developed a prototype locomotive and a short demonstration section of track, then found investors, forming the Mount Washington Railway Company in the spring of 1866, and started construction.

[9] The route closely followed a mountain trail that had been established earlier in the century by Ethan Allen Crawford.

[10] Despite the railroad's incomplete state, the first paying customers started riding on August 14, 1868, and the construction reached the summit in July 1869.

[25] From 1986 to 2017, the Cog Railway was controlled and owned by Wayne Presby and Joel Bedor of Littleton, New Hampshire.

The Bedor and Presby families also owned the Mount Washington Hotel and Resort in Bretton Woods for the period 1991–2006.

These individuals were responsible for a complete revitalization of the railroad, with the assistance of Al LaPrade, a mechanical engineer whose career began at the Portsmouth Naval Shipyard.

[citation needed][31] In the early days of the railway's construction, the workers wanted to minimize time when climbing and descending the ramp, so they invented slideboards fitting over the cog rack and providing enough room for themselves and their tools.

The Boston & Maine Railroad restored Old Peppersass at its Concord shops following the Fair to make a commemorative trip for the railway's 60th anniversary.

After ascending to Jacob's Ladder, the locomotive began a planned descent but jumped up and landed to the right of the cog rail when a tooth broke from a gear wheel.

The engine rolled off the trestle while the uncoupled passenger car slid several hundred feet into a large rock.

[35] A flatcar, initially at rest near the summit, sped 600 feet (180 m) down the track and collided with an ascending passenger train carrying 24 people.

[35] The cog railway designs and builds all of its locomotives and passenger coaches at the company shops located at the base of Mount Washington.

Design improvements have replaced the ratchet (gear and pawl mechanism) with sprag clutches and disc brake assemblies.

[44] In 2008, work began on the first diesel locomotive to be powered with biodiesel, with the assistance of a retired mechanical engineer from the Portsmouth Naval Shipyard.

The most common trips on the Cog Railway are between the two main stations, one at the summit and the other adjacent to the operators' logistical and repair base.

Some hikers have been known to wait for the next train in order to expose their buttocks to the passengers, a practice known as "Mooning the Cog."

The advertised, roughly eastbound route uses the Base Road's full length from Bretton Woods.

The steam locomotives on the railway generate large amounts of smoke, nicknamed "Cog Smog".

The company stated that the primary reason the new diesels were built was to reduce the visual pollution caused by the coal-fired steam locomotives, to lower emissions, and to increase the length of time that passengers could spend at the summit of Mount Washington.

[41] Each three-mile (4.8 km) diesel locomotive ride burns approximately 18 US gallons (15 imp gal; 68 L) of B20 (20% biodiesel blend) fuel.