Monday, December 19, 2016

Continuing the Road Diet Conversation

Current configuration of Petaluma Boulevard South
With help from a guest writer, I’ve recently written twice about a proposed road diet on a major arterial in my town.  First, I wrote about the history of road diets, both in my town and elsewhere in the country, and then professional planner Bjorn Griepenburg wrote about how a four-lane to three-lane road diet reduces conflict points between drivers, bicyclists, and pedestrians, yielding a road that is safer with little or no loss of traffic capacity.

The posts, and an upcoming City Council hearing on whether to submit a grant application for a road diet on Petaluma Boulevard South, triggered active conversations.  Not everyone agreed with the proposed road diet, but the discussions have generally been respectful exchanges of facts, suggestions, and opinions.

However, I was traveling much of last week, so missed the opportunity to participate in the discussions.  Others did a fine job of explaining and defending the road diet concept, but there were a few points I wish I could have added to the discourse.

So I identified a few particular comments on Facebook and Nextdoor that caught my eye, copied them below, and will provide the follow-on that I was unavailable to do last week.  I haven’t noted the authors of the comments.  Indeed, I’ve already forgotten who most of them were.  But I have touched up their grammar at a few spots.

Petaluma Boulevard North after road diet
Regarding the previously completed road diet on Petaluma Boulevard North through downtown and extending further north:

“Visit Petaluma Boulevard North between Payran and D Street any afternoon and you are likely to find long backups extending all the way from E. Washington Street to D Street or a block or so south of D Street.”   The author is likely correct, but there are at least three reasons why the observation doesn’t argue against road diets.

First, there was always been some level of congestion on Petaluma Boulevard North.  We don’t have good measures of what the congestion was before the road diet, so can’t necessarily say that it’s worse now.  And recollections to make a point are often based on selective memory so are untrustworthy.

Second, traffic in general is again climbing as the recession retreats into the rearview mirror.  Even if we had perfect data from before the downtown road diet, the data would have been at the depths of the recession and can’t be compared to the congestion today, well into the recovery.

Third, the length of a queue at a red light is inversely proportional to the number of lanes.  A 200-foot single-lane queue today may look worse than a 100-foot queue in the past, but if the shorter backup was in two lanes, the number of cars would be the same. 

“A road eliminates any excess capacity from the system.”  This is an excellent point in some settings, although it may have limited applicability to Petaluma Boulevard South.

Let’s take the example of a well-configured four-lane road that might have a daily traffic capacity of 30,000 trips.  If the current traffic load is 18,000 trips, conversion to a three-lane configuration, usually considered to have a traffic capacity of 20,000 trips, wouldn’t increase near-term congestion, but would eliminate the capacity of road to accept more trips as conditions change.

But Petaluma Boulevard South isn’t a well-configured four-lane road.  I don’t have an engineering estimate, but with the constricted lanes and with cars stopped for left turns blocking following vehicles, its current capacity may not be much more than 20,000 trips.  So there may be little or no excess capacity being eliminated.

Plus, a well-designed road diet can move some trips from driving to biking or walking, reducing the number of trips that must be accommodated.

“If you are going to squeeze two lanes away and turn a major road into a two-lane road, then put in nice bike paths on both sides.”  Most would agree with the sentiment in the abstract, but reality often doesn’t conform to the abstract.

Much of Petaluma Boulevard, both North and South, has a 52-foot curb-to-curb width.  Widening the street isn’t an option because of existing buildings, a desire to retain friendly sidewalks, and the unavailability of grant money for the much greater expense of widening.

So the designers are stuck with the 52 feet.  After allocations are made for parking, without which merchants and shoppers would riot, and the three lanes needed for a road diet to function, there just isn’t room for bike lanes.

City engineers aren’t anti-biking; they just don’t have enough street width to accommodate every desirable street element.  Sometimes the best they can do is to make a street a little bit safer for bicyclists.

Petaluma Boulevard North with center pocket
"The two-car wide parking lane in the middle is too wide.  If they are going to do a road diet, do it, but use the extra space for bike lanes.”  This is another way of lobbying for bike lanes.  However,  the center pocket, generally used by delivery trucks is only 14 feet wide, two feet  wider than most travel lanes, but far short of “two-car wide”.

And the center pocket is absolutely needed for deliveries.  Some argue that all deliveries should be done from the alleys that parallel Petaluma Boulevard North through downtown, but not all retail spaces extend all the way to the alley.  Also, UPS and FedEx won’t use alleys where they might end up stuck behind a truck doing a large delivery.

At least some trucks must do deliveries from the Boulevard side and the road configuration therefore needs to accommodate those trucks without blocking other users of the street.  The center turn pocket is essential.

“Driving practices need to change before road diets can work.”  I once worked with an engineer who, when someone argued that the users of a proposed project needed to change their behavior so the concept could work, who look deeply thoughtful and then ask, “So, our goal is to change human nature and then design the project?”  She was of course correct and her slyly expressed realism forced others to remember that we can only deal with human beings as they are and as they behave.  They may reengineer themselves over time, but we can’t manage or accelerate that change.

Driving is one of those behaviors that we can’t change easily, if at all.  We have to accept driving Behaviors as they now are and to design roadways to accommodate that reality.  Luckily, road diets have often been shown to work with drivers as they now drive.

Turning attention to comments that were directed at the proposed road diet on Petaluma Boulevard South:

“Bike lanes need to be included.”  To the extent that the road widths permit, I agree.  And there are road segments where bike lanes seem a real possibility.  The final decisions won’t be made until after the grant is hopefully approved and design is underway, but I hope that some bike lanes will be included.  But to insist on bike lanes everywhere puts the unattainable perfect above the achievable.

“Without bike lanes, it is a waste of money.  Just lower the speed limit.”  I’m a huge proponent of lower speed limits and have often written about Twenty is Plenty.

But I’ve also written that we can’t lower speed limits arbitrarily.  Speed limits are set by how drivers perceive safe speeds, so to lower a speed limit, we must change how drivers perceive a street.  It’s a goal I hope can be accomplished through the road diet, and I’ve already begun lobbying for a design standard that would help, but under state law the city isn’t allowed to just post a new speed limit.

“Safer for bikes and pedestrians = good; including bike lanes = Great!  <hopeful>.”  This was my favorite comment and captures my position exactly.  Even where a perfect solution is precluded by existing constraints, incremental improvements are still desirable and essential.

Schedule reminder: The road diet hearing will be this evening, Monday, December 19, 7:00 pm, in the City Council Chambers at 11 English Street.  Regardless of how you feel on the subject, try to attend with an open mind.  New and pertinent information will certainly be offered.

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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