Yellow to red

[Speeda]

How is the timing of a yellow light dertermined? Does it have anything to do with the speed limit?

[SpeedyCorky]

course it relates to speed limit. ever seen a traffic light on a 55mph or 65mph highway..? the yellow lasts HELLA long.


also think it has to do w/ the city/county, as yellows in SF are WAY longer than anywhere else in the bay area.

[silversvs]

The City or County traffic engineering spends considerable effort on determning the correct amount of time for a yellow signal. There are many signals that have a short "all red" period as well, where all lights are red for a brief moment. So many factors go into determing the correct length of a yellow light and if there is a need for an "all red" period; such as posted speed limit, actual speeds traveled, environment/location of the intersection, commute congestion, business district, driveways/outlets located within proximity to the intersection, blind or reduced visibility approaches to the intersection, etc etc.

If there are reported problems with the light timing at an intersection we can work with the engineers to adjust them. Same is true if we get a lot of collisions within the intersection.

[antarius]

In general, they stay yellow 1 second for every 10 miles per hour the speed limit is marked at.

However, as silversvs stated, many, many other variables come in to play to change that... so in short, there is no generally accepted method to determining light intervals.

[Steve Stansb]

Yes, BUT, if it is a camara intersection, it has to be a minimum of 4 seconds. Union City, here in the Bay Area, just a few months ago, had to throw out hundereds of red light violations due to the fact that the yellow light was to short! People received refunds and had the cite's removed from their records. Cost the city a few thousand dollars. I have reported three intersections here in Fremont that the yellow is far to short for the posted speed. Two intersections went from a 3 second light to a 5 second light. The third went to a 6 second light.

Originally posted by CBRDAVE
How is the timing of a yellow light dertermined? Does it have anything to do with the speed limit?

[Speeda]

Is ther a vehicle code that specificly talk about the timing for yellow lights. it's just that and the timing for the light is just over 3 seconds. The intersection where these cameras are set up is huge. There is no way a bike or car can make it completely through the this intersection before it turns red. Light located on East hillsdale blvd.

[motorman4life]

Originally posted by antarius
...so in short, there is no generally accepted method to determining light intervals.
That is not correct. There are guidelines set out by the US DOT and the Federal Highway Administration. There are also many studies that are used, in conjunction with the existing guidelines to develop consistent local practices. CalTrans has their own published guidelines and practices for signal timing and a whole cadre of programing engineers that implemement those policies to various degrees of success. :teeth

There is no law requiring a particular yellow signal duration, but the signal timing is based upon reaction time and standard stopping distances anticipated at the prevailing speeds as well as several other factors, including; time of day, pedestiran traffic, anticipated or actual vehicle traffic, right of ways, driveways and queing.

As I see it, the problems come when cities allow the camera enforcement contractors to tinker with the length of the yellow signal. This is where these cities are getting into trouble. IMNSHO.

A good rule of thumb (on what to anticipate as a safe and responsible motorist) is 3 to 6 seconds. As most signal controlled intersections are found in speed zones ranging from 30 to 50 MPH, you can do the math. 1 second for each 10 mph is probably a good rule of thumb +/- 1 second.

[REFERENCE] (http://www.tfhrc.gov/safety/pubs/04091/09.htm#942)

YELLOW PHASE:
The yellow change interval warns approaching traffic of the change in assignment of right-of-way. Yellow change intervals, a primary safety measure used at traffic signals, are the subject of much debate. The yellow change interval is normally between 3 and 6 s. Since long yellow change intervals may encourage drivers to use it as a part of the green interval, a maximum of 5 s is commonly employed. Local practice dictates the length of the change interval.

Current thought is that longer intervals will cause drivers to enter the intersection later and breed disrespect for the traffic signal. One before-and-after study showed that the time vehicles entered the intersection increased with a longer yellow change interval. Additional research is needed to further understand the effect of lengthening the yellow change interval on driver behavior.

RED CLEARANCE PHASE/INTEREVAL:The red clearance interval is an optional interval that follows the yellow change interval and precedes the next conflicting green interval. The red clearance interval provides additional time following the yellow change interval before conflicting traffic is released. The decision to use a red clearance interval is determined based on engineering judgment and assessment of any of the following criteria:
Intersection geometrics.
Collision experience.
Pedestrian activity.
Approach speeds.
Local practices.

The red clearance interval is either set by local policy or calculated using an equation that determines the time needed for a vehicle to pass through the intersection. The equation most commonly used is described in various documents. As intersections are widened to accommodate additional capacity, the length of the calculated clearance interval increases. This increase may contribute to additional lost time at the intersection, which negates some of the expected gain in capacity due to widening.

SIGNAL CYCLES: The calculation and selection of signal cycle lengths requires good judgment on the part of the traffic engineer/analyst. General practice and standardzed guidlines dictate a cycle length between 50 and 120 s. For low-speed urban roads, a shorter cycle length is preferable (50 to 70 seconds). For wider roadways (over 15 m (50 ft)) with longer pedestrian crossing times (greater than 20 seconds), or in situations where heavier traffic is present and left-turning vehicles are not being effectively accommodated, a cycle length of 60 to 90 seconds may be preferable. At high-volume intersections where heavy turning movements are accommodated by multiple phases, a cycle length of 90 to 120 seconds may be most appropriate. However, cycle lengths longer than 120 seconds may be needed at large intersections to accommodate multiple long pedestrian crossings in combination with heavy turning movements, especially during peak periods.

A cycle length of 90 seconds is often considered optimum, since lost time is approaching a maximum, capacity is approaching a minimum, and delay is not too great. Longer cycle lengths may lead to excessive queuing on the approach and will interfere with turning movements (left- and right-turn channelization) if through traffic is severely backed up.

[motorman4life]

Originally posted by CBRDAVE
Is ther a vehicle code that specificly talk about the timing for yellow lights. it's just that and the timing for the light is just over 3 seconds. The intersection where these cameras are set up is huge. There is no way a bike or car can make it completely through the this intersection before it turns red. Light located on East hillsdale blvd.
To my knowledge, there is no law or reference section in the CVC as to the duration of yellow signals.

This issue was covered in another thread recently, but there is no legal expectation that you clear the (other end of the) intersection before the signal turns red.

The law states that any vehicle that has entered lawfully under the yellow (crossed the limit line) has the right to proceed through, so long as there was space on the other end when they entered. The green signal section mandates that you may not proceed on the green until after you have yielded to any traffic that is/was lawfully within the intersection before you start.

[tgrrdr]

Originally posted by motorman4life
There are guidelines set out by the US DOT and the Federal Highway Administration. [SNIP] CalTrans has their own published guidelines ....

[REFERENCE] (http://www.tfhrc.gov/safety/pubs/04091/09.htm#942)

Originally posted by motorman4life
To my knowledge, there is no law or reference section in the CVC as to the duration of yellow signals.

California uses the MUTCD - California Supplement (http://www.dot.ca.gov/hq/traffops/signtech/mutcdsupp/supplement.htm) for the design of traffic control devices. My understanding of the CVC is that the standards in the MUTCD must be followed for traffic control devices on public streets in California.

Caltrans
This Manual on Uniform Traffic Control Devices (MUTCD) California Supplement is published by the State of California, Department of Transportation and is issued to prescribe uniform standards and specifications for all official traffic control devices, in accordance with Section 21400 of the California Vehicle Code.

Federal Highway Administration’s Manual on Uniform Traffic Control Devices (2003 Edition), as amended by This MUTCD 2003 California Supplement is hereby adopted as the standard for all official traffic control devices, in accordance with Sections 21350 and 21400 of the California Vehicle Code. The MUTCD 2003 Edition and the MUTCD 2003 California Supplement supersede and replace the 1996 Caltrans Traffic Manual, as amended, and all previous editions thereof.

These are the "suggested" minimum durations for the yellow interval, based on the approach speed of traffic (generally very close to MM4L's 1s/10 mph). I'm not sure why the text says "suggested" minimum timing and I can't think of any reasons why an engineer would specify a shorter interval.

http://home.comcast.net/~tgrrdr/barf/4D102.jpg

[jbt56]

This is a great topic. As was stated above, some cities have gotten into very hot water for actually SHORTENING the yellow duration (can you say San Diego?) when cameras are installed, thereby guaranteeing red-light running.

Interestingly, a couple of years ago the National Motorists Association ( www.motorists.org ) issued a 'challenge' to any municipality using, or considering, red-light-cameras. The NMA would give $10,000 to any town that did NOT see a 90% reduction in red light running, simply by adjusting their yellow times- no cameras involved. This challenge (or bet, if you will) went out nationally via AP, etc. As of today, NO municipality has ever taken the bet. They know they can make a lot more than $10k via the citations, because like the vast majority of traffic cites, people won't fight them.

[cheezy]

Here's another good rule of thumb: when it turns yellow, prepare to stop.

[silversvs]

Originally posted by jbt56
....... As of today, NO municipality has ever taken the bet. They know they can make a lot more than $10k via the citations, because like the vast majority of traffic cites, people won't fight them.

I know this has been stated over and over in various threads in this forum, but maybe it needs to be mentioned again. Police Departments and Traffic Engineering Depts. are not in the business of making money. Decisions made on enforcement, engineering, signal light duration etc. are made with safety in mind, not generating revenue.

I supervise our traffic unit. I have never been told to write tickets in order to generate revenue. I would not engage in a ticket writing campaign strictly to gain cash for our City. All monies collected from traffic fines go to the City's general fund. Nobody from City Hall has ever come to the PD and stated we needed to do more to generate cash.

I obviously cannot speak for any other agency than mine, but any statement about citations being issued to generate cash are absolutely false.

[Bronto]

Found Yellow light slow and stopping OK during the dry months. On wet roads Yellow lights are a gamble. That's on a MC, in a Car it isn't a problem.
Heh stopping sideways after rear tire broke loose. That's at 50% of emergency braking levels.
Catch 22 autta slow down. But slowing down means getting run over by faster traffic around.

[motorman4life]

Originally posted by Bronto
Found Yellow light slow and stopping OK during the dry months. On wet roads Yellow lights are a gamble. That's on a MC, in a Car it isn't a problem.
Heh stopping sideways after rear tire broke loose. That's at 50% of emergency braking levels.
Catch 22 autta slow down. But slowing down means getting run over by faster traffic around.
I stop a lot of people that I truly believe them when they tell me they did not feel safe stopping or felt they could not come to a stop in time and would have ended up sideways or stopping over the limit line.

Generally this is due to a combination of factors. Primarily excessive speed (keep in mind, the timing on the lights is mostly dictated by the posted speed limit, which is a MAXIMUM speed, not a MINIMUM speed, BTW), late perception (inattention and unnecessary multi-tasking while driving) and poor equipment (bald tires and bad brakes being noted in a majority of the cases… that squeak, squeak, squeak at each stop is metal on metal).

None of these are a valid excuse or even remotely an exonerating factor in a case of running a red light.

On a clear day, if you are going (roughly) the posted limit and have those AMA lightning fast .75s. to above average 1s. perception & reaction times with adequate equipment, you could easily stop in less than 1/3rd the distance you are given by average yellow signal timing. I have done the math and tested the various charts in real world conditions in the course of over a dozen fatal collisions at intersections involving a red light violation and I have yet to find a yellow to short for safe operation by an average motorist, even with less-than-optimum equipment on a wet street!

I know EVERONE thinks they are an “above average” driver or rider… it is one of those odd phenomenon that cannot be adequately explained by science. Ask the worst driver you know to rate themselves on a scale of 10 and I have yet to find anyone rate themselves below a 7.

That said, if you are driving a motorcycle at or above the posted maximum speed limit on city streets in the rain, you are saying you think you are a 9 or 10. At whatever speed, if you are over-braking the rear and unintentionally sliding to a sideways stop on a wet street… Newsflash: You are not even a 6... more like a 4. Just because you kept it upright, does not mean you are a good rider. Lucky rider, yes. Good rider, no.

Class Dismissed. :nerd

[motorman4life]

Originally posted by silversvs
Police Departments and Traffic Engineering Depts. are not in the business of making money. Decisions made on enforcement, engineering, signal light duration etc. are made with safety in mind, not generating revenue. ...any statement about citations being issued to generate cash are absolutely false.
Mucho mojo on that. Ditto for me. Our goal is to reduce accidents, not generate back-door taxes. I write a shitload of tickets and after the state, county, courthouse and processing vendor get their piece, the city's meager portion (about 8 to 10%) does not even cover my employee benefits, let alone my salary, court overtime, safety equipment, in-service training and fuel costs. Tickets are a pain in the ass for the city.

The secret is, a lot of grant money (big $$) hinge on reducing accidents and gaining seatbelt and child car-seat compliance. It is in the city's best interest to reduce accidents, particularly injury and fatal accidents. There are only 3 ways to do this... the "three E's of traffic safety"

Engineering - Education - Enforcement.

Pain in the ass or not, if the roadway is engineered properly and people know what they are supposed to do or how to react to the signs and signals posted... enforcement is the last tool in the box.