the original height of the 2900 saints was , but the maximum height allowed for steam locomotives to work on the mainline by network rail is , because of overhead line clearances. the height of 2999 was therefore reduced, to allow it to operate on the mainline. mainline operation also requires the additional equipment that none of the original members of its class had, including: aws, tpws, otmr & gsm-r. however a later decision from didcot regarding the ceasing of mainline running means that the engine will only see use at didcot and on other heritage railways.