Adaptation Strategies for Managing Recurring Congestion—Adding New Capacity - Road Traffic Congestion - page 247

Fig. 17.10 Improving street continuity reduces VMT

17.2.3.3 Street Spacing

Perhaps the most pervasive congestion problem in suburban areas is the wide
spacing of continuous roadways. The one-mile spacing that is common in many
suburban areas results in heavy turning movements at signalized intersections of
continuous roads. This condition contributes to heavy congestion during peak hours
resulting from both the heavy left turn movements and the 4-phase traf

c signal

operation that is needed to accommodate these turns.
This situation is dif cult to deal with in built up areas (where grade separation is

dif cult to build). But in areas under development it can be avoided by reducing the

spacing to

or mile in each direction of travel. For example, a left-turn volume

½ ¼

of 300 vph — common along many six-lane arterials within a 1-mile grid — becomes

about 75 vph if the grid spacing is mile (assuming the same lane use distribution).

The reduced left-turn volumes will allow more green time for through traf

¼

c and
permits shorter cycle lengths. In this case (where speeds are less that 35 mph and
safety conditions allow) left turns of less than 100 vph, can be accommodated
without exclusive left-turn phases [ 14 ].