What could be the reason for excessive skidding of the tram during start-upand braking?

A 'black rail', colloquially known as 'mada', is a slippery layer of contaminants (e.g., moisture, dust, leaves, lubricants) that deposits on the rail head. It causes a significant reduction in friction between the wheel and the rail. Consequently, particularly in the weather conditions shown in the picture, a tram may be prone to excessive slipping during acceleration and braking.