Proposed construction at the Thames Valley Parkway in the City of London has necessitated a detour route. The original detour, encompassing Talbot St and Grosvenor Street met with opposition from users who proposed an alternate route by way of Gunn Street. Initially the City of London appeared to abandon the original detour in favour of the Gunn Street route. But subsequently the City changed its mind again and indicated that both routes would be posted, allowing users to decide for themselves.

Many opposed the original route because of the danger of sending cyclists through the busy section of Talbot south of Oxford Street. This location also included a narrowing of Talbot Street as it passed through the underpass of the CP railway line just south of Oxford.

In these discussions there has been no recognition that additional dangers exist in the original detour route. In particular the original detour would cause cyclists to ride down the steep downslope of Grosvenor Street into the large parking lot at Gibbons Park. This route has been taken by cyclists in the past and there is no information about the numbers of cyclist collisions and injuries that might have occurred there. Yet, in general, there is no information that is publicly available in London as to how many cyclists become injured from collisions, where those collisions occur, and under what circumstances.

Gorski Consulting has been conducting a variety of testing in recent years on downslopes where cyclists ride in the City of London. This testing has shown that the speed of cyclists is proportional to the steepness and length of these downslopes. While speed is not the only factor in cyclist injury causation it is one of the major factors that cannot be ignored. Of particular concern at the Grosvenor Street downslope is that, upon reaching the bottom of the slope, cyclists enter into a large and busy parking lot. There is a reasonable likelihood that vehicles turning into and out of a parked position will enter into a conflict with cyclists. Cyclists are likely to be difficult to detect by drivers who may be looking in different directions when backing in or out of parking spots. The potential for increased conflicts exists when more cyclists may be directed into the parking lot as a result of the proposed detour route.

This is a view looking west along Grosvenor Street from just west of St George St. This is at the top of the downslope that would carry cyclists into the parking lot of Gibbons Park approximately 200 metres west of St. George Street. Although there is a warning sign suggesting the users of the road keep to a speed of 20 km/h, such an advisement is rarely followed, especially by cyclists whose actions are different from drivers of motor vehicles.
View looking west on Grosvenor Street from approximately halfway down the slope. The portion of the road leading up to the parking lot in the background is the steepest portion of the slope reaching a maximum of about 15.7 % at 175 metres.
View looking east from the Gibbons Park parking lot showing the end of the Grosvenor Street downslope in the background. There is a concern that, with higher numbers of cyclists entering into this area at high speed there could be a conflict with drivers of motor vehicles entering and exiting their parking spots.

Gorski Consulting has conducted some measurements of the downslope of Grosvenor Street between St George Street and the parking lot at Gibbons Park. The distance between these two endpoints is about 200 metres. The slope measurements are noted in the table below.

In comparison the slope at several sites where previous testing has been completed are noted below:

Meadowlily Rd: Distance = 400 metres, Average Slope = 4.99 %, Maximum Slope = 7.34 %

TVP at Trafalgar: Distance = 300 metres, Average Slope = 3.90 %, Maximum Slope = 9.5 %

TVP W of Richmond: Distance = 80 metres, Average Slope = 6.40 %, Maximum Slope = 11.6 %

Speeds of a Trek, hybrid bicycle, were documented as the cycle was coasted from a stopped position. The maximum speed at each of the above sites is noted below:

Meadowlily Rd Maximum Coasting Speed = 42.4 km/h

TVP at Trafalgar Rd Maximum Coasting Speed = 39.1 km/h

TVP W of Richmond St Maximum Coasting Speed = 30.3 km/h

Maximum speeds were also documented of cyclists riding on these slopes as noted below:

Meadowlily Rd Maximum observed speed = 62.72 km/h

TVP at Trafalgar Maximum observed speed = 52.94 km/h

TVP at Richmond Maximum observed speed = 43.37 km/h

If cyclist speeds, such as those noted above, occur at the Grosvenor site then there should be reason for concern. It can be noted that the steepest slope at the Grosvenor site occurs in the vicinity of 175 metres and this is just as cyclists would be approaching the parking lot. With the recognition that they are entering into a parking lot cyclists may apply higher braking at the Grosvenor site. Alternatively there could be cyclists entering into this area who have not ridden down the slope before or have limited experience with it. They might also not comprehend the danger or riding into a parking lot at high speed. Thus there is a reason to conduct testing to explore this potential safety issue.