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Re: What Really Causes Traffic Congestion

Posted by Stephen Bauman on Sun Jul 14 22:23:42 2013, in response to Re: What Really Causes Traffic Congestion, posted by BrooklynBus on Sun Jul 14 22:00:51 2013.

A pedestrian overpass would speed travel for pedestrians not slow it since there would be no waiting for signals to change

What never?


Pedestrian speeds, in addition to being directly related to traffic density, have been found to vary for a wide range of conditions, including individual age, sex, personal disabilities, environmental factors, and trip purpose. Normal walking speeds unimpeded by pedestrian crowding have been found to vary between 150 and 350 ft/min (0.76 and 1.76 m/s), with the average at about 270 ft/min. As a point of comparison, running the 4-min mile is equivalent to a speed of 1320 ft/min or almost 5 times normal walking speed. Walking speeds decline with age, particularly after age 65, but healthy older adults are capable of increasing their walking speed by 40% for short distances. Dense pedestrian traffic has the effect of reducing walking speed for all persons. The smaller personal space limits pacing distances and the ability to pass slower moving pedestrians or to cross the traffic stream.

Photographic studies of pedestrian traffic flow on walkways have shown that individual area occupancies of at least 35 ft2/pr (3 m2/pr) are required for pedestrians to attain normal walking speeds and to avoid conflicts with others. Interestingly, the maximum pedestrian traffic-flow volume is not obtained when people can walk the fastest, but when average area occupancies are at about 5 ft2/pr, and pedestrians are limited to an uncomfortable shuffling gait less than half normal walking speed. At individual space occupancies below 2 ft2/pr, approaching the plan area of the human body, virtually all movement is stopped. When there is a large crowd in a confined space, this density can result in shock waves and potentially fatal crowd pressures.


Movement on stairways is restrained by tread and riser dimensions, added exertion, and greater concerns for safety. These restraints result in lower speeds and lower traffic capacity on stairways than on walkways. Ascending stair speeds vary from 50 to 300 ft/min, with the average at about 100 ft/min, or one-third level walking speed. Descending speeds are about 10% faster than ascent because of the assist of gravity. A much wider variation of individual speeds exists on stairways because even minor vision or joint disabilities can significantly affect climbing or descending movements. For this reason greater attention to human factors and safety requirements is required in stairway design. Most building codes use a 22-in (560-mm) lane width as an egress standard, and multiples of this width are often used in designing stairs. This arbitrary selection can result in inconveniently narrow stairs, particularly in transit facilities where there is heavy two-way movement and people with hand-carried articles. Based on human factors considerations, lane widths on stairs in transit facilities should be in multiples of 28 to 30 in (711 to 760 mm), with a minimum width of 60 in needed for fluid two-way movement.

Average speed on flat surface: 270 ft/min
Average speed on stairs: 100 ft/min


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