This pack contains 4 pieces of 5 mm wide, self-adhesive backed plastic die-cut to fit round the outside of Scalextric Radius 1 45 degree curves (C8202). They also work for SCX Digital track and can be used on tight curves of routed tracks, depending on the radius.
All you need to do is paint the area where you want to position them. Then just peel off the backing paper and press them down around the outside of the curve. You can add grass effect flock afterwards.
White kerbs with raised red rumble strips are also now available for the inside of these corners. See K-R1