When we put 'flat tire' on our defect card, it doesn't mean we have a tire out of air. Flat tire means that our tread has worn unevenly. When we take our coach up to twenty miles an hour, we hear the drums along the Mohawk. A thump thump as the worn or flat portion of the tread goes round and round.
The noise and vibration is not too noticeable as there are so many other distractions and noises around us, such as the rough road surface, we can't tell we have a flat tire! Only on a newly surfaced street, can we tell that we have a flat tire. But there is not too much worry about that! Construction of new condos with upgrade tie-ins to water and sewer leads to the main line, has open trenches, metal plates, and patch jobs galore. When streets are resurfaced, they are only paved a block at a time. This hides the "new" defective tread tire that has been put on a bus that still had a quiet ride when it was tagged for the tire shop. Perfectly round tires are replaced with scalloped ones. I guess there is a good aftermarket for round tires that have not been retread or re-grooved!
Just ask any cyclist about tires and city streets. If you ride on a regular basis, it is only a matter of time before you get heavy duty tires for your bike. The Streets of San Francisco have loose asphalt over metal plates, rail tracks, and road surfaces that show through to the concrete seams below.
Rail tracks can send cyclists flying over the seat like a bucking bronco. The mist and fog don't help either.
The only thing worse that a flat tire on a bus is one on a bike. But the good news is that every bus has a bike rack to take you back to the shop for a new one or just some air. I always give you a free ride if your bike gets a flat on the street. Also, just to let you know, you motorists, or car people, if your car is in the shop, I'll brake of a long one for you for taking mass transit for the first time. The first ride is free!