This view of a cyclist turning onto the Blackfriars Bridge in London was taken on August 23, 2022 at a time when traffic studies were being conducted by Gorski Consulting and Dillon Consulting. Dillon Consulting was officially retained by the City of London while Gorski Consulting performed a study independent of the City. Results of the two studies provide some insight into how data, and the conclusions drawn from them, can vary.

In recent years considerable debate existed in London Ontario with respect to the usage of the historical Blackfriars Bridge located just northwest of the City’s downtown. While there was much opinion there was scarce data to support that opinion. As a result Gorski Consulting commenced a traffic study in the spring and summer of 2022 and its results summarized and uploaded to the Gorski Consulting website. It became known that the City also intended to conduct a long-term usage assessment of the Bridge although what form that study would take and when it would be completed was unknown.

In a report to the City of London dated May 31, 2023, Dillon Consulting reported that it had been retained by the City to conduct a long-term usage study of the Blackfriars Bridge. A brief review of the report showed that Dillon conducted its investigations through a similar time period as the Gorski investigations, both in the spring and summer of 2022. It become possible therefore to examine the findings from both studies and to explore their differences and similarities. The purpose of this present article is to begin that comparison through a review of the general traffic volumes that were documented in both studies.

Among the details reported in the Dillon Consulting report was a Table 6 summarizing their findings from an 8-hour session of observations undertaken on September 29, 2022. That table is copied below.

A somewhat similar summary table was created by Gorski Consulting and this table is copied below. The Gorski data was developed from conducting two-hour observations on five different days, thus resulting in 10 hours of observations.

The reporting of traffic by Dillon during morning and afternoon peak hours, along with a noon-time session day is a standard and accepted methodology.

The Gorski methods were slightly different in that observations were made during five different days, These days were chosen to encompass a diverse range of possible traffic patterns. On May 29, 2022 a session was conducted on a Sunday to document what differences there may be from weekday observations. The other 4 sessions were conducted on weekdays (Monday, Tuesday, Wednesday and Friday) thus allowing a further exploration of changes in traffic during the week. Diverse times of observation were also employed encompassing similar times to the Dillon observations.

Comparing motor vehicle traffic, Dillon reported that a total of 659 units were observed during their 8-hour session, or approximately 82.4 units every hour. In comparison, Gorski reported that a total of 482 units were observed during their 10-hour session, or approximately 48.2 units every hour. Thus Dillon reported at least twice as many motor vehicles per hour as the Gorski data.

With respect to cyclist volumes, the Dillon table did not provide an overall summary of the number of cyclists they observed. Instead they reported the cyclist data in separate columns showing individual motions. A summary was then provided that grouped the pedestrians and cyclists together. We summed the cyclist numbers in the various cells of the Dillon table and this showed that they observed a total of 635 cyclists. The same procedure revealed that Dillon observed 1745 pedestrians. Thus they observed a combined total of 2380 cyclists and pedestrians during the 8-hour session.

In comparison the Gorski table shows that 842 cyclists and 1017 pedestrians were observed in total of 10 hours of observation. A slightly different approach is that Gorski described a separate column of “Non Pedestrians” which encompassed traffic units of various sorts such as persons riding medical carts, e-scooters, etc. and these numbered a total of 70 observations.

Looking at these sums of cyclists and pedestrians, Dillon reported approximately 79.4 cyclists per hour whereas Gorski reported approximately 84.2 cyclists per hour. Thus, at face value, there does not appear to be a major difference in the findings. With respect to pedestrians Dillon reported approximately 218 per hour whereas Gorski reported approximately 101.7 per hour. Thus these pedestrian sums indicate a substantial difference. Dillon reported observing more than twice as many pedestrians as Gorski.


Examining the documentations that Dillon Consulting obtained on September 29, 2022, they reported about twice as many motor vehicles and pedestrians, per hour, as compared to the documentations obtained by Gorski Consulting. Cyclist volumes were approximately similar between the Dillon and Gorski studies.

The Dillon report focused on the efficiency of traffic flows in the vicinity of Blackfriars Bridge while less attention was brought to potential safety concerns at the bridge. This may be related to the scope of their assignment as defined by the City. Little information is available about that scope since the retaining letter from the City to Dillon Consulting is not available. Dillon provided a brief mention of the scope of their assignment in the Introduction segment of their report where they stated:

“Dillon was to quantify the usage of the Bridge by vehicles, pedestrians (ped.), and cyclists, and evaluate the role of the bridge in the transportation network for all users.”

In the Approach segment of their report Dillon indicated that they examined the behaviour of traffic units at the bridge:

“Dillon performed a site visit to the Bridge to observe how vehicles, pedestrians, and cyclists were using the Bridge and identify any unusual behaviour that might be occurring.”

It is unusual that Dillon Consulting did not report safety concerns at the intersection of the pedestrian crossing of the Thames Valley Parkway at the east end of the bridge. Gorski Consulting observed several obvious issues during our examinations and some were reported in articles posted on the Gorski Consulting website. A review of these issues will be made in a separate article that will be posted shortly to our website.