Refer to figure.

ICAO Annex 14
Chapter 5. Visual Aids for Navigation

5.2.3 Runway centre line marking Application
5.2.3.1 A runway centre line marking shall be provided on a paved runway.

Location 
5.2.3.2 A runway centre line marking shall be located along the centre line of the runway between the runway designation markings as shown in Figure 5-2, except when interrupted in compliance with 5.2.1.1.

Characteristics
5.2.3.3 A runway centre line marking shall consist of a line of uniformly spaced stripes and gaps. The length of a stripe plus a gap shall be not less than 50 m or more than 75 m. The length of each stripe shall be at least equal to the length of the gap or 30 m, whichever is greater.
5.2.3.4 The width of the stripes shall be not less than:

— 0.90 m on precision approach category II and III runways;
— 0.45 m on non-precision approach runways where the code number is 3 or 4, and precision approach category I runways; and
— 0.30 m on non-precision approach runways where the code number is 1 or 2, and on non-instrument runways.

Centre line markings are painted visual aids provided on a paved surface.

The centre line helps pilots:

• stay aligned during take-off and landing,
• maintain directional control,
• especially when workload or reduced visibility makes visual cues critical.

This requirement is therefore based on the surface of the runway, not on whether the runway is certified, used for commercial operations, or classified as an instrument runway.

Importantly, the regulation also specifies centre line marking characteristics for non-instrument runways, confirming that an instrument runway is not required.

As a result, whether the runway is used commercially or privately, instrument or non-instrument does not change the basic need for a visual centre reference.