A computer-implemented method of setting a target longitudinal acceleration of a host vehicle relative to a road along which the host vehicle and a leading vehicle are travelling, for use in autonomous control of the host vehicle, the road comprising a plurality of lanes (21A to 21C), the method comprising: determining a lateral position of a model of the leading vehicle in a model of the road, based on a detected position of the leading vehicle; defining a lateral range extending from the model of the leading vehicle in the model of the road, the lateral range extending in a first lateral direction in the model of the road and a second lateral direction in the model of the road which is opposite to the first lateral direction, the lateral range comprising a first lateral subrange, a second lateral subrange and a central lateral subrange between the first lateral subrange and the second lateral subrange, wherein the lateral range is defined so as to increase by increase of at least one of the first lateral subrange and the second lateral subrange with increasing distance between the determined lateral position of the model of the leading vehicle and a lateral position in the model of the road of a centre of a lane among the plurality of lanes in which the model of the leading vehicle is located during a lane change by the model of the leading vehicle from the lane to an adjacent lane of the plurality of lanes; setting a longitudinal range extending from a rear of the model of the leading vehicle in a first longitudinal direction in the model of the road; setting the target longitudinal acceleration of the host vehicle such that, for any longitudinal position of a model of the host vehicle that is within the longitudinal range, the target longitudinal acceleration of the host vehicle is set to: a respective first acceleration value in a case where a lateral position of the model of the host vehicle in the model of the road is within the central lateral subrange; and a respective second acceleration value, which is dependent on a lateral position of the model of the host vehicle in the model of the road relative to the determined lateral position of the model of the leading vehicle, and is greater than the first acceleration value in a case where the lateral position of the model of the host vehicle is within the first lateral subrange or the second lateral subrange. determining a lateral position of a model of the leading vehicle in a model of the road, based on a detected position of the leading vehicle; defining a lateral range extending from the model of the leading vehicle in the model of the road, the lateral range extending in a first lateral direction in the model of the road and a second lateral direction in the model of the road which is opposite to the first lateral direction, the lateral range comprising a first lateral subrange, a second lateral subrange and a central lateral subrange between the first lateral subrange and the second lateral subrange, wherein the lateral range is defined so as to increase by increase of at least one of the first lateral subrange and the second lateral subrange with increasing distance between the determined lateral position of the model of the leading vehicle and a lateral position in the model of the road of a centre of a lane among the plurality of lanes in which the model of the leading vehicle is located during a lane change by the model of the leading vehicle from the lane to an adjacent lane of the plurality of lanes; setting a longitudinal range extending from a rear of the model of the leading vehicle in a first longitudinal direction in the model of the road; setting the target longitudinal acceleration of the host vehicle such that, for any longitudinal position of a model of the host vehicle that is within the longitudinal range, the target longitudinal acceleration of the host vehicle is set to: a respective first acceleration value in a case where a lateral position of the model of the host vehicle in the model of the road is within the central lateral subrange; and a respective second acceleration value, which is dependent on a lateral position of the model of the host vehicle in the model of the road relative to the determined lateral position of the model of the leading vehicle, and is greater than the first acceleration value in a case where the lateral position of the model of the host vehicle is within the first lateral subrange or the second lateral subrange. a respective first acceleration value in a case where a lateral position of the model of the host vehicle in the model of the road is within the central lateral subrange; and a respective second acceleration value, which is dependent on a lateral position of the model of the host vehicle in the model of the road relative to the determined lateral position of the model of the leading vehicle, and is greater than the first acceleration value in a case where the lateral position of the model of the host vehicle is within the first lateral subrange or the second lateral subrange.