Enhanced maps (Emaps) have proven their ability in aiding vehicle navigation, by applying constraints to lateral position of the vehicle. This is actually being demonstrated for instance in the frame of several lane level CVIS applications (Cooperative Vehicle Infrastructure Systems, a 6th Framework Programme Integrated Project). In some other research activities, the road direction between nodes or shape points of digital maps appeared to be of great interest as a possible way to improve vehicle heading estimation. Under this process, one assumes that both the vehicle and the road have most of time the same direction. In this article, we propose that the road geometry is described in Emaps by clothoids and contributes to vehicle location in a Bayesian framework by means of a particle filter. Actually, the road direction is a parameter very easily obtained when the road is precisely depicted by series of clothoids and acts as a strong constraint in the location process. Furthermore, the very challenging question of whether a GPS position should be accepted or rejected in such a filter has also been investigated. A strategy that aims at rewarding GPS instead of dead reckoning in case of lateral deviation is shown, with interesting results in particular for an on-board low-cost gyroscope.