On a dual c'way, lane lines are 2m stripe, 7m gap (7 & 2's). Usually a stud (industry name for a cats eye) is at every other gap (18m c/c), unless the area is prone to fog in which case it is every gap (9m c/c). Edge studs follow the same pattern as lane studs. Green studs at slip road entrance/exit are at 3m c/c.
Single c'ways can have 7 & 2's, 6 & 3's, 4 & 2's or 3 & 6's (according to whether the road is a hazard or not, eg bends, junctions). Studs are normally placed in every other gap. If a solid or double solid white centre line is used, spacing is either 2m c/c or 1m c/c.
Studs should not be used when there is street lighting (except for on motorways).
