By law each entrance to a junction or a crossing must have
a stop line which is a thick solid white line across the entranceto the junction.
As depicted in Fig.
1(a) each stop line spans across all the lanes in one direction.
Vehicles must stop behind this line when the light is red.
Therefore the presence of the stop line serves as a good reference.
However stop lines on city roads are often broken variable width and have poor contrast
with the road color.