A method of generating routes in an area covered by an electronic map is described. The map comprises a plurality of segments representing navigable segments in the area covered by the electronic map, each segment being associated with jam probability data representative of a likelihood of a jam on the segment. The method involves generating a first route between an origin and a destination in the area, and generating at least one alternative route between the origin and destination using the jam probability data associated with the segments in the area. In embodiments jam and non-jam travel time data is used with the jam probability for a segment to obtain a measure of reliability of the segment under given traffic conditions, which is used to generate the alternate route(s).