From Diversey to roughly Armitage (1 mile), the southbound-facing curb lane of Clark St is a bus – and bike-only lane from 7 to 9 AM, Monday through Friday. I’ve rarely seen a bus actually able to use it for more than a block due to parked/standing cars.
There is a sign stating that the lane – otherwise used as parking – is a tow zone at those times.
I even saw a woman trying to pay the parking meter, which did tell her she could not pay – because it is a bus lane…
Enforcing the no-parking aspect of the lane is important since the Clark bus moves a ton of people – about 21,000 daily as of June. For comparison, there are about 12,000 vehicles on Clark daily. Buses are more efficient on Clark St. It is also one of the most-bunched bus routes; having a dedicated lane ensures the bus can move without impediment and without having to weave in and out of traffic.
But that only works with enforcement.
Addendum: The fine for standing or parking in a bus lane is $90 in Chicago.