questionText: To ask the Secretary of State for Transport, what criteria are used to determine when temporary air quality speed limits are used on the M4 near Heathrow.
answerText: National Highways implemented a speed restriction of 60mph on the M4 westbound at junctions 3 to 4 in December 2022 to achieve nitrogen dioxide (NO2) compliance in the shortest possible time.
heading: M4: Speed Limits