The capacity of a highway is suddenly reduced to 60% of its normal capacity due to closure of certain lanes in a work zone. If the Greenshields model describes the relationship between speed and density on the highway, the jam density of the highway is 112 veh/mi, and the mean free speed is 64.5 mi/h, determine by what percentage the space mean speed at the vicinity of the work zone will be reduced if the flow upstream is 80% of the capacity of the highway.