Car navigation controlled by gyro

Hi,

I want to make a straight line walking vehicle controlled by a gyroscope. The car would follow a given angle and
would correct its direction if a disturbance takes it out of the way. However, the gyro gives the angular velocity, so the angle I get by integrating it has an error which increases over time.
How can I reduce this error?

To correct for gyro drift you need an external reference, like a magnetometer to tell which direction is North. That can be problematic if magnetic materials or current carrying conductors are near the sensor.