In multiple European cities now I see taxis being allowed to use the bus lane (while of course regular cars are not).

What's the policy justification for this?

I agree that allowing taxis to use bus lanes in European cities is justified. It helps reduce congestion and speeds up public transport. The political rationale behind this policy lies in enhancing the efficiency and environmental friendliness of urban transport. This approach reduces traffic jams, improves public transport accessibility, and lowers harmful emissions. The policy encourages using taxis as an alternative to private cars, leading to decreased traffic load and better air quality in cities.