The results have now been tabulated with respect to the gaps between westbound vehicles travelling in the right lane of Highway 401 from four videotaping sessions. It can be recalled from previous discussions that Gorski Consulting has conducted videotaping at four sites along Highway 401 in South-western Ontario, as indicated in the figure below.
The videotaping at Elgin Road was conducted in November, 2016 and is not included in the calculations. A second videotaping session was conducted at the Westminster Drive site. Thus we have results from four taping sessions at three sites.
For the present time only about 15 minutes of videotape was examined from each session. Examining all of the video would have taken more effort than could be accomplished in this non-funded research. The results shown in the table below may appear complicated and we will provide some explanation.
As indicated in the upper part of the table, the total numbers of westbound vehicles observed in each of the four videotaping sessions in shown in the upper part of the table as well as a separation between heavy trucks and non-trucks. Medium-sized trucks was included in the “non-truck” category so that we could focus on the involvement of large, air-brake-equipped vehicles from the rest. There were only a couple such medium-sized trucks in each sample so there was not a large part of the sample.
This data only looks at the traffic in the right lane of the highway. There were vehicles travelling the passing, or median lane that are not being considered. To standardize the procedures, a vehicle was counted to be in the right lane when, upon passing the 400-metre-marker, the vehicle was observed to be in the right lane. Vehicles that we in the passing/median lane at the 400-metre-marker that changed lanes into the right lane were excluded from this analysis. Vehicles that were in the right lane at the 400-metre-marker that changed lanes afterward into the passing lane were included in the data. There were not a large number of vehicles that performed these lane changes in the 400 metres of observation.
It can be seen at the right of the upper part of the table that the “Percent Trucks” values vary substantially from one session to the next. This is because we purposely selected days when the percentage of trucks would likely be different. So the “Westminster Drive Oct 30” and the “Graham Road” were conducted on typical weekdays when percentages of heavy truck traffic would be expected to be high. In contrast the “Westminster Drive Dec 2” session was on a Sunday when truck traffic would be low. Also, the “Dillon Road” session was obtained on the Friday after the American Thanksgiving Day holiday when truck drivers would be expected to stay at home for the holiday and therefore the truck traffic was low. This facts need to be kept in mind when drawing conclusions from the data.
In the bottom part of the table we show the results from the actual gaps that were observed in traffic. The gaps were noted by using one of our markers (usually the Zero marker) that was placed on the roadside next to a video camera. The timecode was documented when the front end of a vehicle passed the marker and then a second timecode was documented when the rear-end of the vehicle passed the marker. The same was done for the next approaching vehicle. Then the elapsed time was noted from the rear of the first vehicle to the front of the following vehicle. This is the time gap.
The “Average Time Gap For All Vehicles” is the value of the time gap between individual, westbound vehicles divided by the total number of vehicles observed in the westbound right lane. To some degree this is a measure of the density of traffic in the right lane.
We purposely focused on those vehicles that were following closely behind a leading vehicle. This can be considered to be unsafe because it may provide insufficient time to react to changing traffic conditions such as sudden slowing or stopping of traffic. The presence of large heavy trucks is a problem because they require a longer stopping distance but also because their large width and height makes it difficult for drivers following them to see the roadway ahead. We selected those observations where the time gap was 2.0 seconds or less and this is what is shown in the table.
As an example using the “Westminster Drive Oct 30th” data, of the 91 trucks that were observed in the right lane, 19 of those trucks were observed to be following a vehicle ahead by 2 seconds or less. Of the 46 “Non-Trucks”, 11 of those were observed to be following at 2 seconds or less. Thus, in terms of percentage, 20.9 percent of trucks were following a 2 seconds or less and 23.9 percent of non-trucks was following at 2 seconds or less. These percentages are shown for all four sessions below:
Westminster Drive Oct 30th: Trucks =20.9, Non-trucks= 23.9
Westminster Drive Dec 2nd: Trucks=14.1, Non-trucks=24.2
Graham Road: Trucks=15.9, Non-trucks=20.8
Dillon Road: Trucks=4.8, Non-trucks=16.2
We can also take all four sessions as a whole and indicate that of the 260 observations of heavy trucks 40, or 15.4 percent were observed to be following a vehicle at 2 seconds or less. For the 272 observations of non-trucks, 58, or 21.3 percent were observed to be following a vehicle at 2 seconds or less.
We can also examine what kind of vehicles were being followed close behind, as shown in the table below. This data is separated into the individual sessions as well as summarized for all four sessions combined.
Although the numbers are small they suggest that the most common combination of one vehicle following less than 2 seconds behind another is where a non-truck is being followed by another non-truck. The least common is where a heavy truck is following a non-truck. These results may be surprising considering the comments made by various drivers of passenger cars and light trucks claiming that aggressive truck drivers attempt to drive them off the road by their close tail-gating. These preliminary data may suggest that it is more common that the drivers of passenger cars and light trucks and van are the ones who do more tail-gating than the drivers of heavy trucks. However the small numbers of observations in this study make these judgments non-conclusive. Exploration of the full 2 hours of videotape from each session might help to solidify what is the actual case.