Gorski Consulting has now completed the documentation of 560 instances of driver response to a red signal turning green at numerous intersections throughout London, Ontario. A dashcam was used in a vehicle that was positioned behind the drivers who were stopped at a red traffic signal. When the signal turned green the delay in time was noted when the brake lights of the vehicles extinguished.
The overall average delay for all 560 observations was 0.70 seconds. However there were a number of additional facts to consider. For example, 110 drivers, or 19.6 %, reacted by more than 1.0 seconds. And 86 drivers, or 15.4 %, reacted in 0.4 seconds or less. It is generally understood that a person should not be able to react to a simple stimulus such as a green light in less than 0.40 seconds therefore this suggests that many of these drivers were already releasing their brake pedal before the signal turned green. This was evidenced further by noting that vehicles were observed to crawl forward while the signal was still red even though the brake light was still illuminated. Thus this confirmed that these drivers were releasing their pressure on the brake pedal before the signal turned green, likely in anticipation of the signal turning green.
As some drivers took as much as 3.0 to 4.0 seconds before extinguishing their brake lights this affected the overall average of 0.70 seconds. Similarly some vehicles could be seen extinguishing their brake lights 3.0 to 4.0 seconds before the signal turned green and this also affected the overall average. In an attempt to clarify the data, we conducted a frequency count to see where the most observations were clustered and this is shown below.
Response greater than 0.2 but less than 0.3 seconds = 11 observations
Response greater than 0.3 but less than 0.4 seconds = 31 observations
Response greater than 0.4 but less than 0.5 seconds = 44 observations
Response greater than 0.5 but less than 0.6 seconds = 54 observations
Response greater than 0.6 but less than 0.7 seconds = 55 observations
Response greater than 0.7 but less than 0.8 seconds = 37 observations
Response greater than 0.8 but less than 0.9 seconds = 23 observations
Response greater than 0.9 but less than 1.0 seconds = 17 observations
Thus, looking at the above breakdown, the most common response delay is between 0.5 and 0.7 seconds.
It needs to be noted that this response time is different from the response time to start a vehicle in motion, which should take a longer time. Thus, once a brake signal is extinguished the driver’s foot needs to lift completely off the brake pedal and transition over to the accelerator pedal. Then the driver needs to depress the accelerator pedal and a further delay in the vehicle mechanical and electronic systems occurs before the vehicle can begin moving forward. Other research has indicated that delay to start a vehicle in motion is likely in the range of 2.0 seconds.
This research shows how much difference exists in drivers, some who are very conscious of the traffic signal and want to begin accelerating forward as quickly as possible, versus those drivers who do not appear to be attentive to the status of the traffic signal and wait a substantial time before accelerating forward. Those late responders, approaching 20% of the total, may be an indication of the extent of driver lack of attention to basic cues around their driving task. Although there is much discussion about driver distraction by in-vehicle instrumentation and cell phones, there is no way tell, from this research, why these late delays occurred. It might even be an indication of the general level of inattention that exists in this 20% of the overall population of drivers.
When drivers fail to detect the activation of a green signal while stopped the opposite might also be true: that these same drivers might not be attentive enough when they are approaching a green signal to detect when the signal has turned to amber and red. Hopefully drivers are a little more attentive when their vehicle is in motion and they are approaching a traffic signal but how much more attentive they are needs further study. It is likely that many drivers may not purposely travel through a red traffic signal but that their lack of attention may be the cause of that action. Thus certain penalties for such infractions may be of lessened effect when the solution might be in studying a driver’s level of vigilance and ability to focus their attention. Such deficiencies are not generally tested in new drivers and certainly not in drivers who have been on the road for many years.