As used in the general provisions and in Divisions 1 (commencing with Section 50), 2 (commencing with Section 900), and 2.5 (commencing with Section 1800), “maintenance” includes any of the following:

1. (a) The preservation and keeping of rights-of-way, and each type of roadway, structure, safety convenience or device, planting, illumination equipment, and other facility, in the safe and usable condition to which it has been improved or constructed, but does not include reconstruction or other improvement.
2. (b) Operation of special safety conveniences and devices, and illuminating equipment.

3. (c) The special or emergency maintenance or repair necessitated by accidents or by storms or other weather conditions, slides, settlements, or other unusual or unexpected damage to a roadway, structure, or facility.

   The degree and type of maintenance for each highway, or portion thereof, shall be determined in the discretion of the authorities charged with the maintenance thereof, taking into consideration traffic requirements and moneys available therefor.