Introduced in late 1958, the PDR1/1 set the standard for years to come. This example, dating from June 1960 and first operated by Plymouth City Transport, is one of the earliest preserved examples of this first round of Atlantean buses. It was initially offered with the Leyland 0.600 9.8 litre engine, the same as used in the then popular standard layout PD3 double decker front engine bus. Later, Leyland offered the 0.680 11 litre engine as an alternative, and the smaller option continued until 1965. This example was fitted with the 9.8 litre engine.

The revolutionary design relied on the transverse rear engine position, pneumo-cyclic semi-automatic gearbox, spiral bevel drive coupled to a pair of helical spur reduction gears, with the differential being offset to the nearside.

This layout made double decker one person operation (OMO) possible, and the end for the conductor was nigh.