Friday, December 11, 2015

Looking More Closely for the Coded Messages Being Sent to Drivers

I’ve often written about the nonintuitive but ultimately logical method by which speed limits are set in California.  For those new to the subject, speed limits are established by the speeds at which cars travel when drivers are unaware of a speed limit.  So if most drivers demonstrate by their actions that a road should be driven at 30 mph, the speed limit under California law would be 30 mph, with only a few exceptions.

This standard for setting speed limits has interesting implications for urbanists and for all who care about traffic safety.  Specifically, drivers will travel at the maximum speed at which they feel comfortable.  Therefore, making drivers less comfortable would have the effect of reducing both travel speeds and speed limits.

After decades of seeking to improve the driving experience and road safety by widening streets, removing street trees, and requiring off-street parking, we now understand that the primary result was greater speeds that often reduce safety.   Instead, we should have been increasing driver discomfort by narrowing streets, planting street trees, and encouraging on-street parking.

I have a neighbor who regularly complains about two aspects of the cars on our street.  First, she grumbles that too many cars speed.  Second, she protests when people she doesn’t know park at the curb in front of her home.  Perhaps I’ll find an opportunity over the holiday season to explain to her that more parked cars, especially badly parked ones that encroach into the travel lane, would slow traffic, so her two complaints are inconsistent.  Watching her splutter can be a Christmas gift to myself.

(Another aspect of our street, which I’ll broach if I really want to mess with the neighbor, is that the street, like many older streets in Petaluma, has received supplemental lifts of asphalt over the years without a full depth repaving.  The result is road section that is significantly humped in the middle.  Most of the neighbors complain that the City owes us a full depth repaving.  But the humped section reduces driver comfort and thereby reduces traffic speeds, a point that I’d enjoy making.)

I’ve written much of this before, but a recent comment by a young North Bay planner cast a more personal light on speed limits.  In describing the Petaluma home in which he’d grown up, he noted that safety on his childhood street was quite good.  Because of the narrow width and extensive street parking, the few drivers who traversed the street did so with caution.

I knew the exact street segment to which he was referring, although I don’t travel it often because I don’t find it a friendly street to drive, proving his point.

His comment induced me to take a short tour of Petaluma, camera in hand, to document a range of street sections.  The top photo is from the street on which the planner spent his youth.  The second is also from the Oakhill Brewster neighborhood, around the corner from the first street.  Although the second street is wider, both feel confined by parked cars and both have the centerline humps that also slow speeds.

It was interesting to note that there are few if any speed limit signs within Oakhill Brewster.  The street geometry keeps drivers below 25 mph, which is the generally lowest speed limit allowed by California, so there was no need for the signs.

In contrast, I then visited the site of an eastside apartment project now under planning review.  At the hearings on the project, the neighbors complained strenuously about traffic speeds.  I’ve written several times about the issue, most recently here.  The upper photo is in front of the proposed apartment site; the lower is around the corner on a crossing street.

The different between the two sets of photos is striking.  The absence of street parking and/or greater street width in the latter set increases driver comfort and speed.  The absence of a significant centerline hump does the same.  It’s not surprising that the neighbors near the latter two photos have complained about travel speeds.

And I remain convinced that the reduced lane widths I’ve been pushing for the neighborhood could be an essential step toward reducing driver comfort and thereby reducing speeds.

Next time you’re bothered by speeding in a neighborhood, take a look at the street section, consider it relative to these photos, and conceive ways to make drivers less comfortable.  Then push your solution at city hall.  The city folks will be so shocked to have someone with answers rather than complaints that they might be willing to give a good listen.

The past few days have been rainy, a pleasant change for drought-stricken California.  Some will argue that, although it’s still too early to be sure, the end of the drought may be close.  I disagree, for reasons I’ll explain in my next post.

As always, your questions or comments will be appreciated.  Please comment below or email me.  And thanks for reading. - Dave Alden (

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