The drivers, who were members of the Gauteng taxi association, were in a minibus driving along the R74 when unknown gunmen launched an ambush and opened fire.
Mowasalat has showcased its taxi, bus and limousine services at its pavilion at the Traffic Week celebrations.
Some taxi drivers want dedicated parking spaces for their vehicles on service roads along some of Doha's major roads, hospital compounds and government offices that receive a large number of visitors.
A strike in the Indian capital by thousands of Uber and Ola drivers demanding better pay has paralysed the ride-hailing services that have grabbed business from traditional taxi and rickshaw operators with their cheaper fares.
Residents of some of the newly developed residential areas in and around Doha say they often find it difficult to get a taxi, especially early in the morning and late in the evening.
Hundreds of taxi drivers blocked access to Lisbon airport and snarled traffic in the Portuguese capital on Monday as they protested against app-based ride-sharing companies such as Uber.
Mowasalat, the public transport company, has expressed regret for any inconvenience caused to customers on July 18 and 19, due to disruption in dispatching taxis by its call centre.
Female motorbike taxi drivers in headscarves zig-zag through heavy traffic in the Indonesian capital Jakarta, the latest two-wheeled transport service for women making a dent in the male-dominated world of ride-hailing apps in the Muslim nation.