Whenever I am driving I try to speed through the light when it is yellow and it is always stressful trying to get through before it becomes red. Street crossing lights have a countdown number that tells the walker how long until the light changes. Why isn't a similar thing implemented on traffic lights?
Introduces Calculation, Gamification, and Additional Cognitive Load to the Interaction
In addition to the practical factors presented by Michael Lai, I suggest a key reason for not including this feature is that it introduces potentially negative factors to the interaction.
Ideal User Reaction
"Light changing. Red soon. Prepare to stop".
Potential User Reaction
"Light changing. 25 seconds. Car in front not slowing. Hmmm. 23 seconds. 200ft to intersection. Can I make this? 20 seconds..."
This isn't to suggest that this type of reaction isn't possible with the typical simple color system, but I'd argue that the 'Ideal User Reaction' (above) is more likely to result from a simple color system.
The additional thinking time and cognitive load of a system that introduces timing, when spread across all levels of driving ability, aggressiveness, competitiveness, and risk adversity, would likely result in a net negative affect on driving behavior.
Actually there are examples of this in different countries, or at least I have seen it in Shanghai before.
There are a lot of reasons behind whether systems like this can be implemented or not, but a traffic engineer might provide a more accurate answer. But in general these are the considerations that I know:
- Cost: probably the number one consideration since these devices are quite expensive to install and maintain
- Feasibility: traffic regulations and rules may prevent the logical or practical implementation of these systems
- Impact: you could argue whether pedestrians just end up modifying their behaviour instead of becoming more safety conscious, and whether drivers would end up just modifying their behaviour as well.