A computer-implemented method of determining a position of a vehicle within a transport network and determining a route option taken by the vehicle, comprising: obtaining track geometry data indicating track geometry of at least a part of the transport network; determining, based upon the track geometry data and sensor data from at least one sensor (25, 27) arranged to output a signal indicative of a motion of the vehicle, that the vehicle is approaching a junction; determining, based upon the track geometry data, a plurality of route options from the junction; generating a plurality of Bayesian estimation filter algorithms each associated with a respective one of the plurality of route options and configured to estimate a position of the vehicle based upon the track geometry data indicative of the associated route option, the plurality of Bayesian estimation filter algorithms being configured to estimate a position of the vehicle based upon the output signal of the at least one sensor, wherein the plurality of Bayesian estimation filter algorithms are configured to output data indicative of probabilities of the vehicle taking the associated route options; monitoring the output of the plurality of Bayesian estimation filter algorithms as the vehicle passes through the junction; and determining the route option taken by the vehicle by selecting one of the plurality of route options which presents the highest probability based upon the output of the plurality of Bayesian estimation filter algorithms, characterized in that the output data comprise innovation values calculated by the plurality of Bayesian estimation filter algorithms based upon pseudo-measurements of the associated route options, the pseudo-measurements of the associated route options being determined based upon the track geometry data indicative of the associated route options, wherein the pseudo-measurements comprise a pseudo-measurement of an attitude of the vehicle along a track defined by the track geometry data indicative of one of the route options and wherein the pseudo-measurement of the attitude of the vehicle is calculated based upon a tangent of the track defined by the track geometry data at the estimated position of the vehicle. obtaining track geometry data indicating track geometry of at least a part of the transport network; determining, based upon the track geometry data and sensor data from at least one sensor (25, 27) arranged to output a signal indicative of a motion of the vehicle, that the vehicle is approaching a junction; determining, based upon the track geometry data, a plurality of route options from the junction; generating a plurality of Bayesian estimation filter algorithms each associated with a respective one of the plurality of route options and configured to estimate a position of the vehicle based upon the track geometry data indicative of the associated route option, the plurality of Bayesian estimation filter algorithms being configured to estimate a position of the vehicle based upon the output signal of the at least one sensor, wherein the plurality of Bayesian estimation filter algorithms are configured to output data indicative of probabilities of the vehicle taking the associated route options; monitoring the output of the plurality of Bayesian estimation filter algorithms as the vehicle passes through the junction; and determining the route option taken by the vehicle by selecting one of the plurality of route options which presents the highest probability based upon the output of the plurality of Bayesian estimation filter algorithms, characterized in that the output data comprise innovation values calculated by the plurality of Bayesian estimation filter algorithms based upon pseudo-measurements of the associated route options, the pseudo-measurements of the associated route options being determined based upon the track geometry data indicative of the associated route options, wherein the pseudo-measurements comprise a pseudo-measurement of an attitude of the vehicle along a track defined by the track geometry data indicative of one of the route options and wherein the pseudo-measurement of the attitude of the vehicle is calculated based upon a tangent of the track defined by the track geometry data at the estimated position of the vehicle.