# Electronic Components/Traffic Lights.

Question

7 Segment LED

Traffic Lights
QUESTION: Dear Deirdre

http://en.wikipedia.org/wiki/Traffic_light
http://www.engineersgarage.com/electronic-circuits/traffic-light-signal-555
http://www.555-timer-circuits.com/traffic-lights.html
http://en.wikipedia.org/wiki/Seven-segment_display

In the typical sequence of color phases:

Green Light : Illumination of the green light allows traffic to proceed in the direction denoted, if it is safe to do so

Orange Light : Illumination of the orange/amber light denoting prepare to stop short of the intersection, if it is safe to do so

Red Light : Illumination of the red signal prohibits any traffic from proceeding

Query
-----

Can a Single 7 Segment LED Display be used as an alternative
to the above three traffic lights with modifications in the control circuit ?

i.e.

0 Indicates Stop -> Similar to Red Light.
1 Indicates Stop Short Of -> Similar to Orange Light.
2 Indicates Proceed -> Similar to Green Light.

i.e. Instead of three light signals (three LED for each color red,orange and green) use of
a Single 7 Segment LED Display (indicates Number instead of colors) as source of Traffic Lights.

What are the Pros and Cons if this can be achieved ?

Do you feel showing Human Being Symbols (Red and Green Color)
would be a Bottleneck in the Single 7 Segment LED Display ?

In that Case Number 8 for Human Being Walk Stop Symbol and Number 9 for Human Being Walk Start Symbol can be used ?

Thanks & Regards,
Prashant S Akerkar

ANSWER: 7-segment displays wouldn't work as well. For people with vision difficulties (some are color-blind - some don't have perfect vision), the three different colors in different positions work best to provide the most information at a distance. It's easy to see a red light / green light (or top / bottom, left / right, etc) even from 1/4 mile. It would be more difficult to discern a number at such a distance.

This is one reason why three separate lamps are used - those who are color-blind can still see if it' the top, middle or bottom lamp that is illuminated.

---------- FOLLOW-UP ----------

QUESTION: Dear Deirdre

Do you feel showing Human Being Symbols (Red and Green Color)
would be a Bottleneck in the Single 7 Segment LED Display ?

In that Case Number 8 for Human Being Walk Stop Symbol and Number 9 for Human Being Walk Start Symbol can be used ?

OR

Better would be to Display Character S for Human Walk Stop and P for Human Being Walk Proceed instead of numerical 8 and 9 respectively ?

Could a 7 segment display white has an edge over Colors - can be useful
for Color Blindness people ?

http://www.lc-led.com/Catalog/department/36/category/49/1

Another interesting survey would be :

Numbers, Alphabets (characters) V/S Colors Recognition Pattern - Which is easier to interpret ?

References
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Do you feel Traffic Lights integrated with Wireless Loud Speakers at some Strategic Locations on Highways, Roads, Junctions could be useful ?

With the help of Wireless Speakers, signal announcements (Proceed, Stop, Slow Down) as well as general announcements to be made to vehicle drivers as well as the general public. This announcements will be controlled by the Traffic Control Room.

Thanks & Regards,
Prashant S Akerkar

Actually, I think that a dramatic shift in traffic signals could cause a great deal of confusion, and using a 7-segment type display requires more mental processing than a simple colored light. It requires more concentration on the display, which can increase the time needed to respond to the lamps. With the current system of color and position, a simple glance - even from a distance, is all that is required to discern the status. Even in less than ideal viewing conditions, with the shroud around the lamp, it's easy to determine which is illuminated.

With a 7-segment display, as viewing conditions worsen, and the distance from the display increases, it becomes more difficult to determine which character is displayed. For example - in foggy conditions, it's still fairly easy to determine for all but color-blind people, which color lamp is illuminated - even from a distance; the fog diffuses the light, but the color is still visible. With a 7-segment display, at least with a single color, that advantage disappears.

On the other hand, it is possible to build a display with multi-color lamps, and the combination of color and symbol might be of use.
Questioner's Rating
 Rating(1-10) Knowledgeability = 10 Clarity of Response = 10 Politeness = 10 Comment Dear Deirdre Thank you. Thanks & Regards, Prashant S Akerkar

Electronic Components

Volunteer

#### Deirdre Hebert

##### Expertise

I can answer most questions regarding electronic components, what they are and how to use them.

##### Experience

I worked for a number of years in the electronic component testing industry, designing and building automated test equipment for the electronic manufacturing industry.

Publications
Numerous technical manuals for the equipment we built.

Education/Credentials
UNH, CCAF and others

Past/Present Clients
General Electric, Motorola, Ford, Sensonor and others.