I use a rule of thumb in my book and continue to promote this. Because mini-roundabouts are so
interactive, drivers may be forgiven when occasionally
they all look at one another wondering who is going to make the first
move. This three-way stand-off is relatively common
and it has to be said that different drivers will accept
very different conditions before entering a busy
mini-roundabout. |
Frank Blackmore invented a capacity rule
based on the area of the junction. He argued that the
capacity was in direct proportion to the linear size of
the junction expressed by a formula that summed the entry
widths and added a value for the square root of the
remaining area. This was based as much on his research on
the TRL test track as anything else; it suggests the
possible capacity if the area is used most efficiently.
It relates to a fundamental formula that I illustrate in
my seminars: |