There are currently major rail works underway in Oxfordshire which will result in railway line closures through Oxford station for a two week period from 7-22 July 2018.
For full information see: www.gwr.com/travel-updates/planned-engineering/oxford2018
Given this notice, staff should be able to explore other options in good time. Where there are particular difficulties, for example a route on which no suitable bus replacement is provided, you may need to consider allowing staff additional flexibility. This might involve adjusting their working hours e.g. coming in late and making up the time, or exploring the options laid out in the severe weather policy http://www.admin.ox.ac.uk/personnel/cops/severeweather/