Bottlenecks - Road Traffic Congestion - page 75

Railroad Grade Crossings: Railroad grade crossings are common in many
suburban areas. Whenever trains pass, motor vehicle and pedestrian/bicycle
movements are stopped. Also in this situation queues are formed and their
length is critical

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in determining the congestion impacts on the connecting

roadways.

7.2.2 Operational Bottlenecks

Midblock and intersection con fl icts cause bottlenecks that contribute to congestion

especially during heavy traf icts are the result of loading and

unloading of goods from the streets and are the result of cross traf

c periods. These con fl

c, as well as

turning vehicles and pedestrian con fl icts at signals.

7.2.2.1 Curb Parking and Goods-Loading Conflicts

On-street curb parking in business districts frequently results in congestion by
reducing the number of lanes that are available for moving traf

c. In addition,
double parking during peak periods — often by delivery and courier vehicles — have
an even more detrimental on movement. They block several traf c lanes, and during

heavy periods can cause spillback on approaches to the bottleneck.
This condition is generally found where:

On-street parking is permitted during busy traf c periods

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There is inadequate enforcement of curb parking regulations

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There are frequent double parkers.

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Where a street has two lanes in a given direction, and where parked vehicles
occupy one lane there is at least a 50 % loss in capacity.

7.2.2.2 Intersection Conflicts

Intersections of major streets are often the focal points of traf c congestion during

peak periods of travel. The many con fl icts — between pedestrians, cyclists, and

motorized traf c; between through and cross traf c, and between through and

turning vehicles are major sources of congestion.
As shown in Figs. 7.16 and 7.17 , at a typical four-way intersection there are 32
vehicle - vehicle con fl ict points and 48 pedestrian-vehicle and bicycle-vehicle

con fl icts.