The Department collects some information on the number of passengers who use trains at selected stations, however it does not collect this information for Preston Park. Train operators use commercial passenger data and various modelling methods when making changes to the timetable. This data takes into account time of day, day of week and passengers using stations other than the one which is on their ticket.
In addition, the Office of Rail and Road publishes annual estimates of the total numbers of people entering, exiting and changing trains at each station in Great Britain. These show that in 2016/17, the latest year for which information is published, there were 527 thousand journeys (of which 211 thousand were season ticket journeys) that started or ended at Preston Park.
The methodology takes into account situations where passengers are travelling to or from a different destination to that on their ticket. For example, in the 2016/17 wave of ‘Estimates of Station Usage’, 88,372 entries and exits were reallocated from Brighton to Preston Park.
You can find the data and methodology report through this link: http://orr.gov.uk/statistics/published-stats/station-usage-estimates