The tender for the then-new franchise in 2015 originally permitted the continued use of Pacer trains, as it was judged by the Department for Transport (DfT) that a new rolling-stock order represented "poor value for money.".

[18] However the House of Commons Transport Select Committee described the continued use of Pacer trains as "unacceptable" and recommended that the Secretary of State use franchise specification power to include the need for a new rolling-stock order.

[13][22] CAF was selected by Arriva, as it was the only manufacturer able to build both diesel and electric (Class 331) multiple units from the same platform, Civity, thus increasing familiarity for drivers and reducing maintenance costs once in operation.

All trains are fitted with an automated audio information system, as well as display screens - six in each carriage, ensuring all passengers have an unobstructed view of at least one.

[31] Northern selected a "wide and spacious" vestibule area to allow for quicker passenger flows when boarding and disembarking to minimise dwell times and thus reduce delays.

In maintaining an objective for the interior to be spacious, seats are cantilevered off the body frame and there are no internal doors, with open gangways between carriages.

As a result, they are fitted with Automatic Selective Door Operation (ASDO) for use on routes where station platform lengths are not sufficient to fully accommodate the train.