Dear Parking Guru,

I often feel lucky to find parking at all in SF. Last week I did, but then it was all ruined because when I returned to my car I found a ticket on my windshield. I am a victim for an issued citation for "parking on grades."  I had no idea what this meant and did fruitless, extensive research on it, until I found your articles on 7x7. You wrote that when parking on any street of 3% grade or more, a car’s wheels must be curbed. I parked on Ortega between 34th and 35th.  It seemed like an almost flat street. I cannot afford this ticket so I wanted to contact you and hear your thoughts because you are the Parking Guru! Thank you so much for the time and attention that you give to helping people.

Regards,
Flummoxed
 
Dear Flummoxed,

It is indeed a boomerang effect, after the victorious feeling of finding an available and legal parking spot, only to return to your car and find a ticket, especially for a non-obvious violation. If it brings you any comfort, you are not alone. Last year 64,985 people experienced the same sinking feeling when receiving a ticket for: T58A , aka “Parking on Grades” or “Blocked Wheels.”  This violation accounted for 4.25% of all parking tickets given out last year.  Some of them were ticketed erroneously. So it is always good to check out the facts.

However, I am sorry to report that you are not one of those lucky people to have been erroneously cited.  According to the official Surveyed Streets of San Francisco, to which I’ve made a link, the grade of that particular block where you parked is 4.86%. Barely steep enough to roll an apple down, but steep enough to get you a ticket. The theory being that if for some reason your car’s transmission were to come out of park, or its parking brake were to fail, the street is steep enough for your 3,000 pound vehicle to do begin rolling and do some damage. Turning the wheels toward the curb allow the curb to act as a safety net.  

Why is it determined that 3% grade is the magic number? I have no idea. I envision a Far Side picture of a group of SF engineers in lab coats and clipboards in the 1950s doing tests rolling round objects down the streets. But, I wager that it was a little more scientific than that. A 3% grade is a 1.72 degree slope, which is probably the minimum slope where a stationary vehicle’s mass, combined with the force of gravity, would overcome the surface friction of the tires against the asphalt and begin to move.
 
Inertia is kind of cool actually. All sorts of things are hanging in balance, resisting and yielding to the forces of gravity…fruit hanging on trees wanting to drop but held in place by their stems; water in rivers flowing with gravity; and even your 16-pound head balancing on the tiny surface area of your spine, wanting to drop to the ground, but being held all day in exquisite balance.
 
I’m sure that understanding the physical theory that cost you $55 is of little consolation. But perhaps you’ve saved a few thousand other people from getting the same ticket. So for that, there will probably be a little boost in your parking karma. And, we all got to flashback to 9th grade physics and see that we really can use math and science in ordinary life.
 
David LaBua is the author of Finding the Sweet Spot, and founder of VoicePark, the mobile app that guides you by voice to the closest available on-street or off-street parking spot in real time.