This paper extends work previously performed in the area of integrating reduced-cluster MEMS IMU and GNSS measurements in urban navigation conditions. These reduced-cluster IMU configurations are implemented since the typical dynamic conditions of land vehicles are well known. Specifically, this work utilizes a single-axis gyro for heading, a tri-axis accelerometer for velocity updates, and a commercially available software GPS receiver. The reduced inertial cluster is mounted in-line with the vehicle forward-right-down axes. Previous work by the authors has addressed the estimation of IMU mounting angles relative to the vehicle frame [1]. The vehicle frame is assumed parallel to the road surface. Therefore, any vehicle pitch and roll angles are due to local terrain variations.is work utilizes a single-axis gyro for heading, a tri-axis accelerometer for velocity updates, and a commercially available software GPS receiver. The reduced inertial cluster is mounted in-line with the vehicle forward-right-down axes. Previous work by the authors has addressed the estimation of IMU mounting angles relative to the vehicle frame [1]. The vehicle frame is assumed parallel to the road surface. Therefore, any vehicle pitch and roll angles are due to local terrain variations....