Spokes are measured in millimeters. Their width is measured according to an arcane "gauge" system that applies nowhere else on a bike. Rim diameters, meanwhile, are sized according several unrelated schemes that don't include gauges or metric units.

It comes as no surprise, therefore, that sign-hangers working for the San Francisco Municipal Transportation Agency seem to have become flummoxed when hanging "Bicycles Allowed Full Use of Lane" signs. One gets the feeling they mixed up the metric system and the U.S. system of yards and feet, bolting the signs 7 meters high even though the city's standard calls for hanging them at seven feet.

Last week The Snitch informed readers that San Francisco's difficulties getting motorists to share the street with bicycles might be solved by finding more prominent locations for the dozens of signs now suspended around the city that look like this:


​
Though they're everywhere, most people have never seen one, because they're typically positioned high in the air, as if intended for seagull traffic.

I asked SFMTA  spokeswoman Kristen Holland why the city would post signs in a way that nobody could see them. She eventually got back with the following note:

"I spoke with our traffic engineers. Generally, the bottom of any single post sign placed in the sidewalk area must be at least 7 feet off the ground for safety reasons.  This is standard for all regulatory, warning, and guide signs. Low level, dual post parking signs are used to allow new trees to grow; those are generally replaced with 7 foot high signs when the trees get taller."

However, an actual look at the signs shows that many of them are actually placed far closer to seven meters high, more than three times higher than the standard Holland cites.

​
As noted last week, a motorist straining to figure out what this all-but-invisible sign said would actually be of more danger to cyclists than someone who was looking where he or she was going.

Why are the "allowed full use of lane" signs meant for the birds?

The traffic engineers apparently told SFMTA spokeswoman Holland that it was proper to make the signs invisible to motorists.

"There is no separate or "special" policy regarding bike sign placement. The actual placement of each individual sign is often dependent on available space.  If a resident believes that a sign is in the wrong place or deficient in some way, we ask that they report it to 311. The SFMTA Sign Shop can then make adjustment where feasible."

So there's your homework assignment, readers: Stay on the lookout for "allowed full use of lane" signs. For every one you find one bolted higher than seven feet, dial 311 and ask to have it moved to a visible location.

The life you save may be your own.