1) Velocity: As mentioned before, the velocity estimates computed from the Lidar data (≈ 0.8 km/h) are worse than the estimates of the radar (≈ 0.38 km/h).
The fusion clearly exploits the good precision of the radar velocity (≈ 0.34 km/h).
Remember, that the radar can only improve the component of the velocity that is parallel to the direction of the radar.
If the Lidar velocity has a perpendicular nonzero velocity component it could negatively effect the precision.