DO THE MATH - Short Amber Times

 

The Dilemma Zone

All yellow lights in Winnipeg are 4.0 seconds long and are timed while assuming that the law regarding yellow timing is permissive.  A permissive law means that vehicles are legally allowed to enter the intersection up until the end of the yellow duration and clear during the red.  

Under this type of law , the yellow must only be long enough to allow vehicles that are too close to the intersection to stop (already within the stopping distance of the stop line) at the point when the yellow is first displayed, to enter the intersection before the red.  

The stopping distance is determined by three variables,

-the initial speed,

-the rate of deceleration and

-the perception/reaction time. 

According to various Institute of Transportation Engineers (ITE) documents, the rate of deceleration is -10ft/s2 and the perceptions/reaction time is 1 second used for determining minimum yellow duration.  

Using the information, we can see if Winnipeg yellows are adequate for each speed zone.  

80 km/h Intersections

A vehicle travelling 80k km/h is moving at 73 ft/s.  With a deceleration rate of -10ft/s2, it will take 7.3 seconds for that vehicle to stop.  

The average rate of speed during that time is going to be 36.5ft/s.  While stopping, the vehicle will travel 367ft (36.5 ft/s x 7.3s and when that is added to the 736 ft travelled during the 1 second perception/reaction time, it is found that the stopping distance at 80 km/h is 339 feet.  

With a 4.0 second yellow, vehicles are only able to travel 292 feet. (73gt/s x 4.0 sec) during the 4.0 second yellow meaning that there are some vehicle s already withing the stopping distance (can't stop) when the yellow is fist displayed that are also unable to enter before the red.  

This creates a 47 foot area where a vehicle can't stop or go and is know as the Dilemma Zone

70 km/h Intersections

A vehicle travelling 70 km/h is moving at 64 ft/s and will take 6.4 seconds o stop.  

During the stopping and perception/reaction time, the vehicle will travel 267 feet.  With a 4.0 second yellow, vehicles are only able to travel 255 feet during the duration of the yellow creating a 12 foot Dilemma Zone.  

The Dilemma Zone still exists at 70 km/h intersections but it is not as large as in the 80 km/h intersections.

 60 km/h Intersections

A vehicle travelling 60 km/h is moving at 55 ft/s and will take 5.5 seconds to stop.  

During the stopping and perception/reaction time, the vehicle will travel 204 ft.  With a 4.0 second yellow, vehicles are able to travel 219 feet during the duration of the yellow.  

When stopping distance is less tan the distance that can be travelled during the yellow duration, the opposite of a dilemma zone is crated which is called an option zone.  

The option zone is the area where a vehicle can both stop or go when the light initially turns yellow.  

At 60 km/h intersections, the option zone is 15 feet long.

50 km/h Intersections

A vehicle travelling 50 km/h is moving at 46 ft/s and will take 4.6 seconds to stop

During the stopping and perception/ reaction time, the vehicle will travel 149 feet.  With a 4.0 second yellow, vehicles are able to travel 182 feet during the duration of the yellow, creating a 23 foot option zone.  

Due to the lower rate of travel, the option zone is larger than it is for a 60 km/h intersection.  

 


 Add this...

Winnipeg us the only known major city in Canada that doesn't increase the duration of the yellow signal for higher speed intersections.  

This creates what is know as a Dilemma Zone for drivers in the 70 and 80 km/h zones who get caught into a situation where they can't safely/reasonably stop or go.  

To adapt, Winnipeg drivers caught in these zone must brake harder than the values accepted by engineering standards.  

Drivers who are unable to do this will get caught by the red light cameras on the occasion they get caught in the Dilemma Zone.

This is why cameras in the 80 km/h zones issue 600% + more tickets than those in lower speed zones.  

The Dilemma Zones represented in this writing are the absolute minimums.  They can be considered even larger (and the option zones smaller) by the standards used in some other jurisdictions.  

Better Math, for when it's about safety...

The perception/reaction time used for these calculations at he minimum 1.0 seconds.  Some jurisdictions calculate using a 1.5 second and sometimes up to a 1.8 second perception/reaction time which increases the stopping distance.  

In addition, many jurisdictions calculate their yellows using the travelling (85th percentile standard) speed instead of the posted limit.  

When this is done, the yellow is normally calculated using the speed limit plus 7 mph.  If considering the higher travelling speeds or longer perception/reaction times, the yellow at Winnipeg's higher travel rate intersections are even more inadequate and therefore, dangerous. 

A problem with these calculations is that they rely on drivers being allowed to legally enter the intersection on a fresh yellow and clear the intersection on the red, under the permissive yellow.  

But, the Manitoba Highway Traffic Act states that: 

Yellow traffic control light or arrow at intersection

88(5)   When a yellow or amber traffic control light or arrow is being shown at and intersections by a traffic control signal following or accompanying a green traffic control light,  

(a) the driver of a vehicle at or approaching the intersection and facing the light or arrow shall not enter the intersection, unless he can leave it before a red traffic control light or such other signal as next follow, begins to be shown...

The law means that Manitoba has what is called a restrictive yellow law and is the only province known to do so.  Under this law, yellow lights not only have to be long enough for traffic that is caught within stopping distance of stop line to enter the intersections before the red, but must also be able to clear the  intersection.  

Conclusion...

To engineer more safe intersections, yellow lights in Winnipeg need to be timed to remove the Dilemma Zone in higher speed areas and as long as the HTA remains as it is, must be even longer to allow traffic to clear the intersection before the red.  

That is, if safe traffic flow, adherence to sound engineering practices and fair enforcement are the objectives.

 


 

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