Bath is approximately south-east of the larger city and port of Bristol, to which it is linked by the A4 road, which runs through Bath, and is a similar distance south of the M4 motorway at junction 18. The potential new junction 18a linking the M4 motorway with the A4174 Avon Ring Road will provide an additional direct route from Bath to the motorway. The city introduced a Class C Clean Air Zone on 15 March 2021, which charges the most polluting vehicles £9 per day (and up to £100 per day for coaches and HGVs) to drive in the city centre. It is the first pollution road charging zone outside London in the UK.