In an earlier post I listed something like 44 different types of sight distance (see here). Even this list is not complete. For example I recently came across the term “sight distance in motion” (SDM), a parameter used in reference to the design of facilities for cyclists. One source (ref. 1993) says that SDM :
“…. could be called the comfort visibility zone when cycling. It is the distance that a cyclist needs to see ahead in order to make riding feel safe and comfortable. Research has determined this to be the distance a cyclist covers in 8 to 10 seconds i.e. between 50m and 80m at typical cycling speeds”.
Another source (ref. 745) says more or less the same, and refers to research from CROW in 1993, whilst a third (ref. 1937) also quotes the values of 50m and 80m for SDM.
(Ref.1993) also says that “SSD is the distance that a cyclist needs to see a hazard, react to it and come to a halt. This is shorter than the SDM”. For example, (Ref. 1937) quotes a recommends 25 m for SSD at 30 km/hr and 80m for SDM.
(Ref. 1993) gives a range of values for SDM, which are shown in the following table.
I am not sure why a cyclist needs three times the SSD to feel safe and comfortable (or even how “safe and comfortable” is measured. There is also the question that, if SDM is a valid parameter in the design of routes for cyclists, why is it not also a valid parameter in the design of routes for cars and trucks (etc.).
745 – UK, LTN 2-08 Cycle infrastructure design; Department for transport, October 2008
1937 – UK, Cardiff cycle design guide, Cardiff cycle network, 2011
1993 – UK, Design portfolio B.04 junction and forward visibility; cycling england, 2008