Do We Ignore Speed Advisory Signs? – More Results

Three days ago Gorski Consulting posted results from videotaped observations of vehicles passing through a curve in the fall of 2009. Those results showed that the average speed of vehicles passing through the curve was 75.2 km/h, or over 15 km/h higher than the posted sign indicating an advised speed of 60 km/h. We then indicated that in the fall of 2019 the speed advisory was reduced to 50 km/h and we asked readers whether drivers were likely to reduce their speeds due to the reduction in the advised speed. Well, analysis of videotaped documentation just after the sign change in the fall of 2019 has now been completed and we have those results.

Videotaping using multiple, synchronized cameras was conducted on October 16, 2019, at the north curve of the S-curve of Clarke Road in northeastern London, Ontario. 100 observations were documented over a period of about 24 minutes. The results indicated that the average speed of these 100 vehicles was 72.8 km/h, or about 23 km/h higher than the advised speed of 50 km/h. As observed 10 years ago, not a single vehicle was observed to be travelling at or below the advised speed. However two vehicles were observed to be travelling below the old, advised speed of 60km/h and those are shown in the frame below.

The above vehicles were the slowest ones in all the observed testing. It is likely that the Pick-up truck was travelling so slow because its motion was interfered with by the slow-moving truck. This is a common problem in evaluating what speed drivers select. Drivers cannot go any faster than the vehicle they are following so this tends to reduce the average speed. To deal with this confound Gorski Consulting made some adjustments to the data as follows:

1. Observations were removed in those instances where the following vehicle was within 5 seconds of the lead vehicle. Thus the observation of the Pick-up truck in the above frame was removed.
2. The following vehicle had to be travelling below 72 km/h in order to be removed from the study. In this way we kept those instances where the following vehicle was travelling at above average speed because the lead vehicle was travelling at above average speed and there is less argument that the following vehicle’s speed was interfered by the slow-moving traffic ahead.

By making this adjustment, 10 of the 70 observations of slow-moving vehicles from 10 years ago were removed from the data. Similarly in the October 16, 2019 study, 20 of the 100 observations were removed from the data. The revised results indicated that the average speed in 2009 was 76.7 km/h whereas in 2019 the average was 74.5. Given the small numbers of observations the reduced average of about 2 km/h could be attributed to small-sample variance or it might also indicate that a true, but slight, reduction in speed was obtained with the reduction in the advised speed. But what significance does that have in terms of the overall safety of the public? Clearly drivers do not follow the advice of the posted sign. They did not follow that advice ten years ago, and it is our observation that, in general, where ever and whenever, drivers do not obey posted speed limits unless they are forced to do so.

During the short time that Zygmunt Gorski was a member of the City of London Community Safety and Crime Prevention Committee in 2019, similar data was presented for discussion from testing performed within a school zone in east London. That Gorski Consulting study showed that drivers were ignoring the posted reduction in speed of 40 km/h. Instead of allowing this study to be debated the City refused its attachment to the agenda of the Committee meeting. Similar actions by the City involving the Transportation Advisory Committee led Zygmunt Gorski to resign from both committees. Actions like these demonstrate the resistance that officials have to making a realistic assessment of the dangers posed in their traffic systems.

While there is considerable propaganda about the gains made through “Vision Zero” approaches to traffic safety, the reality is that there is still resistance to change that affects public road safety. Many officials maintain the unreasonable belief that a simple change in posted speeds will result in an increase in safety on a road segment or within a safety zone. Studies by Gorski Consulting continue to demonstrate that this belief is unrealistic. Yet officials continue in their attempts to block studies, such as those performed by Gorski Consulting, that demonstrate the unreasonableness of these beliefs.