No one likes to be backed up at a traffic light, but sometimes that’s as good as it gets. If it happens on Mendocino Avenue, College Avenue or Guerneville Road, it’s best to sit back, relax and leave things in the hands of the “smart signal.”

Two Road Warrior readers had similar questions, answered by Santa Rosa’s traffic engineer, Rob Sprinkle.

Question: As a Santa Rosa driver, I’m amazed and frustrated by the traffic lights in town. They seem designed to impede traffic, not facilitate it. In most cities, if you are driving on a major thoroughfare, going the speed limit, you make a number of lights and then all the lights turn red at once and the cross street lights all turn green. In Santa Rosa, it’s possible and frequent to miss two, three, four lights in a row on major streets like College Avenue, Fulton Road, Guerneville Road. Is there something about the lights in Santa Rosa I don’t know? Is there something the traffic engineers don’t know? – Craig

Question: Could you ask the SR city traffic folks why the heckypeck they can’t adjust the timing of the left turn light from Mendocino southbound onto College eastbound so that more than 3 or 4 cars can make it before the light turns yellow? It seems that if the first car doesn’t start moving the second the light turns green, then it moves to yellow pretty quickly. And since that intersection has such a long cycle, it seems like drivers waiting in the left turn lane somewhat zone out. Yesterday I was the 4th car and had to sit through two cycles before I could turn. –Kathy McMorrow

The simple answer is that a computer decides how long the turn light stays on, says Sprinkle. “When Kathy went through, traffic may have been so busy it stole time away from the turn light to help keep through traffic moving,” he said.

The traffic signal at the Mendocino/College intersection is one of 46 in the city that are smart enough to decide for themselves how many cars are in each lane and how much time to give them. (The others are strung out at other locations along Mendocino, College and Guerneville Road.)

Using adaptive traffic control technology, the signal measures volume in each direction and, within a cycle that can last up to 120 seconds, determines how many seconds to give in each direction. In the left turn lane, if it doesn’t detect a car after 2.5-3 seconds, it moves on to the next phase and adds a little extra time there.

As the volume goes down, so does the length of each cycle. The day Sprinkle answered this question, the cycle was down to 111 seconds while remaining synchronized with the light at College and Humboldt Avenue.


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  1. Angry Biker

    A motorcycle is just invisible in the left turn lanes, no car behind you your screwed, no green, so I just go when the getten is good!. Looks like they will NEVER fix this problem.

    November 20th, 2013 9:40 am

  2. Kathy

    Appreciate you asking my question but the answer makes absolutely no sense to me, given what happens routinely at that intersection.
    First of all, the traffic signal at College and Mendocino can’t be all that “smart” if there are eight or nine cars in the left turn lane and the signal allows pnly two to turn left.

    Furthermore, the left turn signal on the opposite side–the one that allows northbound cars from Mendocino to turn west onto College–is far less “smart” and usually stays green on the left turn lane after the signal opposite it has turned yellow/red. Therefor the through traffic that Sprinkle refers to just added to the next phase, because the next phase is the traffic going straight across College in both directions. If what Sprinkle is saying is true, then the northbound traffic on Mendo crossing College would be given a green light sooner, and it’s not, both sides only turn green after the second left turn light has stopped.

    So again, I think there’s a setting wrong with the turn light going east onto College from Mendocino, and if the first or second car in line doesn’t hit the gas immediately, then the 5-8 cars behind the at busy times are going to end up sitting through 2-3 cycles, which is just dumb.

    November 20th, 2013 5:44 pm

  3. G

    In Petaluma, at the ‘major’ intersection of McDowell and Washington, there is also traffic signals that “think for themselves( sic ). There can be at times a dozen or more vehicles waiting to turn left/west off McDowell only to have the signal allow only 2 to 3 vehicles go through, and if you’re unfortunate to be in the back of the line, you must wait for at least 4 cycles.
    Make it based on the amount of vehicles, not a time limit.

    November 20th, 2013 9:46 pm

  4. robert srafford

    Get out of your cars and ride a bike. Simple solution! Also ban suv and large gas guzling V8 vehicles. If we did so children would have a low death and diabetes rate, humans as a species could have low stress and be active and healthy in the community.

    November 21st, 2013 9:40 am

  5. Kathy

    Robert, riding a bike would not solve the problem, in fact you’d probably have to sit through even more cycles before you could turn left because the “smart” sensors that are too dumb to notice the line of cars surely wouldn’t recognize a bike is waiting.

    Oh wait, maybe you’re one of those cyclists who don’t think red lights apply to you? Nah, that can’t be it.

    November 21st, 2013 12:42 pm

  6. Angry Biker

    Traffic engineer, Rob Sprinkle needs to be replaced! apparently he is not reading the comments here and not addressing the matter at hand, Lights still not fixed!

    November 22nd, 2013 10:35 am

  7. Redwood

    Relax! It’s only Santa Rosa, and nothing good is on TV tonight anyway. Plus, there are DVRs now.

    Just kidding. I’m all wound up about the lights as well, but almost consider it a game to know which ones work, and which ones don’t work.

    The traffic people I’ve met have been really good folks, and they are applying what is handed to them, by some really good folks at City IT (promise that I work(ed) for neither.

    The quickest light is going northbound from Ridgeway and trying to cross Steele Land to get toward county center. If you are riding a bicycle the system thinks you are at the speed of a car, so there is hardly enough time to clip in a get across before the light turns red.

    And, the “killing right gree arrows” are no fun at all. If you are stopped at a light, on a bicycle, going straight, and right next to the right hand turn lane, you are in a bad position. The green right turn arrow goes on, and you are now having cars trying to make that light, while you are stopped. If you try to be more in the middle of the lane that is going straight, to get further away from the killer right turn lane, and the light goes green when cars are 200 yards away, they may not see you at all.

    Whew, got that out.

    Now, folks, I propose a solution: Lead with a smile and know you are already in one of the best places on the plant. You are stuck, yes. But you are mired in the Garden of Eden!

    November 22nd, 2013 4:55 pm

  8. Jack

    I will agree with Kathy, the turn signals at Mendo and College are the worst in the area. None of the other major intersections alluded to are as bad as this one.

    I often left turn from eastb. College onto northb. Mendo, typically later in the evening after the evening commute. And it can take a few cycles to clear. On a few occasions I have seen the left turn signal only trigger every other cycle despite waiting cars blocking the forward traffic.

    I’d like clarification on where the detectors are. I had assumed they detected cars waiting behind the white line, but the full turn lanes have failed to trigger a green arrow. Where is the magical 2.5-3 seconds being measured?

    Do I have to start laying on the horn as soon as I see the green, in order to have a chance of making through in a reasonable time?

    November 22nd, 2013 7:21 pm

  9. Naomi Williams

    Kathy, I totally agree with you about that light. It’s gotten so bad that if there are three or more cars waiting to turn left, I’ll just go straight and then turn left at Cherry St before working my way back to College.
    Seems like a pretty stupid light to me.

    November 25th, 2013 6:21 am

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