Bottlenecks - Road Traffic Congestion - page 67

Fig. 7.1 Example of bottlenecks resulting from lane imbalance. a Converging roadway two lanes
merge into one. b Converging roadway six lanes merge into four. c Converging roadway four
lanes merge into two

Examples of lane imbalance are shown in Fig. 7.1 : (a) two travel lanes
margining into one; (b) six lanes merging into four; and (c) a 4-lane roadway
narrows to 2 lanes for a short distance.
A common source of freeway congestion comes from where the number of
entering lanes on two merging freeways exceeds the number of departing lanes
(Fig. 7.2 ). This condition results in recurrent congestion.
A similar problem occurs where a highly traveled entry ramp joins the main
freeway lanes without any increase in freeway capacity.
Figure 7.3 shows an example of the lack of lane balance along the Northbound
Gowanus Expressway in Brooklyn, NYC. The merge points of the Prospect
Parkway and the Belt Parkway with the Gowanus Expressway result

in high

congestion levels every weekday morning in the peak hours.

Figure 7.4 shows the pattern of lane convergence along I-95 (southbound) in
Connecticut, between Stamford and New Haven. As a result of this condition there
is signi

—

cant amount (intensity, duration, and extent) of daily congestion along this
section of the expressway.