Why Dont We Make Streets Safe Now, And Figure Out The Details Later?

At the vision zero meeting yesterday I asked about adding leading pedestrian intervals for all traffic signals in Mountain View.


A Leading Pedestrian Interval (LPI) typically gives pedestrians a 3–7 second head start when entering an intersection with a corresponding green signal in the same direction of travel. LPIs enhance the visibility of pedestrians in the intersection and reinforce their right-of-way over turning vehicles, especially in locations with a history of conflict.

I found staff’s answer to my question unsatisfactory.

“No it’s not just a software change, we need to look at all the timing and all the operations of all the streets”

Sounds to me like it is just a software change, but the current process in place requires you to consider the timing and etc.

“We have to take into consideration delays it will cause to pedestrians on the opposite street”

This confused me a lot when I heard it. But I think I figured it out. The assumption I had is the signal timing would remain the same, just peds get a head start. The assumption staff has is that the amount of time given to vehicles will remain the same, so every phase of every cycle will be longer, thereby causing delays to pedestrians on the opposite side of the street.



So I understand that staff and the traffic engineers have spent a lot of time optimizing the timings of the light to balance the traffic flows and optimize for different times of day and etc. It is interesting and difficult work. Adding a few seconds delay would disrupt all those calculations.


Is it vision zero or not? Isn’t pedestrian safety more important than traffic flow?

If the city really wanted, they could add Lead Pedestrian Intervals right now, and then rework all the traffic flow analysis after.

  • Streets would be instantly safer
  • The effect on traffic flow would be worse for a while
  • The engineers would be able to re-optimize the timings eventually

There is a choice between two processes

Option A:

  1. Figure out the most dangerous intersections
  2. Re-work all the timings and traffic flow analysis
  3. Make the changes - streets are now safer

Option B:

  1. Change all traffic signals now, reds are a few seconds shorter for vehicles, streets are safer immediately
  2. Figure out the most dangerous intersections
  3. Re-work all the timings and traffic flow analysis

My frustration is the city does not even recognize option B exists.

I know which option I would choose



  • LPI may not be appropriate for all intersections, but in general it there is a traffic light at an intersection it was put there for safety, and our roads have not become more safe over time

  • NACTO recommends bulbouts and no right on red in addition to LPI. I agree. These can also be done relatively quickly and cheaply.