A year on, the mayor says queues are "bad memories" but some say it has cut passing trade.Read more
It allows drivers to check whether a vehicle will be charged for driving into the city centre when the CAZ comes into effect in July.
The proposals are to bring in fees for older vehicles, which release high levels of toxic emissions, that are driven within the city's ring road.
The service went live on the Department for Transport's website on Wednesday after it was initially expected in January.
As more cities declare climate emergencies, we look at how Glasgow aims to cancel out its carbon footprint.