The height of the western part of the dam (the 'crown line') over the is 5.5 metres above Amsterdam Ordnance Datum (, NAP). This high crest line is necessary due to large wave run-up, with the dike designed to permit some flooding at very high water levels. Space was reserved on the crown of the dam for the conversion of the N59 into a four-lane motorway, with a parallel road for other traffic. Due to a policy change in the 1970s, the four-lane motorway was never built.
