Hypothesis 1: White cars are less likely to come to a complete stop at stop signs because they are more likely to be seen by other cars.

Hypothesis 2: Fewer cars would come to a complete stop on a weekday than a weekend. This is because people are busier on a weekday than a weekend.

To formulate our hypotheses, we did a literature search. Stop signs are a common way to increase the safety of drivers and pedestrians at intersections. A US study showed that 70% of crashes at a stop sign intersection were because drivers did not obey the stop sign rules.¹

We found a study conducted by Monash University in Australia. They found white cars were less likely to be involved in car crashes compared to some other colours of cars (black, blue, grey, green, red and silver).² In fact, the study found that white cars are 12% less likely to be in an accident. This may be because white cars are more visible, and therefore less likely to be involved in car accidents.

A second study analyzed traffic safety data colleceted by the Strategic Highway Research Program 2 (SHRP2).³ This study analyzed whether cars stopped at stop signs, just like ours. They found that only 20.2% of cars fully stopped at stop signs.  They were also able to look at the age and gender of drivers, as well as the time of day. 

Therefore, we decided to see if at our community intersection, if white cars were less likely to stop at the stop sign because it is considered a safer car colour, and if there was an association between stopping behaviour and whether it is a weekend or weekday.

Hypothesis 1: 

Our independent variable: Colour of the car

Our dependent variable: Stopping behaviour

Our definition:

Stop: full stop at the intersection, needs to accelerate to get going again. This means the tires stopped turning at one point.

Rolling stop: slows down when nearing the intersection, but does not completely stop. This means the tires did not stop turning but they were turning more slowly.

No stop: does not stop or slow down.

Hypothesis 2:

Our independent variable: Day of week (weekday vs. weekend)

Our dependent variable: Stopping behaviour using the same definition as Hypothesis 1.

We chose a T-junction at Scenic Acres Link and Scurfield Drive NW as it is one of the major entry/exit points into our neighbourhood. Data was collected by positioning ourselves near the intersection, but not where we would distract drivers. Cars were identified by colour and we decided if they stopped, rolled or did not stop, by tally marks.

Data was collected over 7 visits to the intersection (November 9, December 7, December 21, December 28, March 1, March 5 and March 12) either in the morning or afternoon for between 10-30 minutes each. Observing times on November 9 and December 28 overlapped between investigators, but were done independently. Two observation periods were on weekdays, the remainder were on weekends

We counted the tally marks from our observation sheets and put the information into a spreadsheet with the help of our parents. We observed 1,372 cars over the 9 sets of observations (2 sets had overlapped observation periods). Six hundred and eighty-two (682) cars came to a complete stop.

Half of the cars we observed came to a complete stop. This was higher than the rate (20%) reported in the Strategic Highway Research Program 2 study in the United States³. We observed cars at an intersection in our tneighbourhood which may be different from the ones in the United States study.

We looked at the percentage of cars that came to a full stop by white cars and other coloured cars. We also looked at the full stopping rate by weekday and weekend.

Hypothesis 1:

We found that 53% of white cars came to a complete stop, which was higher than the 49% that we observed from the other colours. Our findings did not support our hypothesis. We wonder if people who drive white cars chose them because they are more visible during most driving conditions. These drivers are more safety conscious and are more likely to stop.

Hypothesis 2:

We observed 61% of cars stopped during our weekday observations; whereas 48% of cars stopped during the weekend. Our findings also did not support our hypothsis. It may be because more cars are around during a weekday so people are forced to stop to wait for other cars to clear the intersection.

Limitations:

Our study was only conducted during the day with good weather and road conditions. Results may be different at night, when visbility is poor on the roads or if the ground was covered in snow. Some previous studies looked at any relationship between the age/gender of the drivers, but we did not collect this data.

Only half of the cars we observed came to a complete stop. During our observations, white cars were more likely to come to a complete stop than other coloured cars. We also found that cars, regardless of colour, were more likely to stop on a weekday than a weekend.

We cannot rely on drivers coming to a complete stop at stop signs since only half of the cars in our study stopped. We need to be careful when we are near intersections. We will continue to check both ways and make sure that the cars come to a stop before we cross the street.

Our definition of car coming to a complete stop is a subjective observation. It can also be impacted by the angle at which we looked at the cars. We compared our tallies on the 2 days that we observed the cars together. We noticed a difference in stopping rates (45% vs. 57%). Since the observer with the higher stopping rate completed weekday observations, the findings can be impacted by how we counted “complete” stops.

1. Retting, R. A., Weinstein, H. B., & Solomon, M. G. (2003). Analysis of motor-vehicle crashes at stop signs in four U.S. cities. Journal of Safety Research, 34, 485–489.

2. Newstead, S and D'Elia, A. "An Investigation into the Relationship between Vehicle Colour and Crash Risk" Monash University Accident Research Center Report 263, May 2007.

3. Liu, C and Zhang, W. (2022) Exploring stop sign running at all-way stop-controlled intersections with the SHRP2 naturalistic driving data. Journal of Safety Research, 81, 190–196.

Header Image from: 

https://www.portland.gov/transportation/traffic-operations/stop-sign-overview

Images in the graphs are build-in icons in Microsoft Excel

We would like to thank Mr. Daniel Clovis at Scenic Acres School, Flora Stephenson and Suzanne Sawyer for their support in completing this project.

In the spirit of reconciliation, we acknowledge that this project was done on the traditional territories of the Blackfoot Confederacy (Siksika, Kainai, Piikani), the Tsuut’ina, the Stoney Nakoda Nations (Chiniki, Bearspaw, Goodstoney), the Otipemisiwak Métis Government (Districts 5 and 6), and all people who make their homes in the Treaty 7 region of Southern Alberta.