![]() ![]() A staged or nighttime evacuation can also be used to reduce congestion. (Cities with advanced signal systems can do this remotely.) Temporary signs can direct cars to alternate routes or instruct them to use carpool lanes indiscriminately. Signal lights can also be adjusted to allow more time for cars to pass through a traffic-laden thoroughfare. Finally, planners must figure out how to tell motorists that they can use those contraflow lanes. Then the cars leaving the city must have some way to get to the contraflow side, which can be tricky if there are dividers. First, every single entrance to the contraflow side of the highway must be closed off. This strategy-known as “contraflow”-typically requires a great deal of advance planning. As Mimi Swartz describes in her “Escape From Houston” dispatch, traffic was reversed on some stretches of I-10 so that cars in all lanes headed out of Houston. Transportation departments in the Gulf Coast states have worked out special evacuation plans to do just that. Traffic planners try to ease congestion by upping highway capacity. Reduced capacity in one stretch of highway creates a bottleneck for the higher-capacity stretches nearby. If conditions are less than perfect-if too many cars are on the road at the same time-then capacity can drop. Pretty much anything that could affect the speed of traffic gets included in capacity calculations: the number of interchanges, for example, or the number of trucks on the road, or the width of the shoulders and lanes. ![]() Hills and slopes reduce capacity, as do out-of-state drivers who are less familiar with the local road system. Increasing the number of lanes on a highway adds capacity. Traffic engineers can calculate the “capacity” of a given stretch of road: the number of cars that may pass through every hour under peak conditions. What’s causing all this congestion?īottlenecks, breakdowns, and reduced highway capacity. Traffic jams have extended for up to 100 miles. More than 2.5 million people have tried to evacuate their homes in advance of Hurricane Rita, according to a government official in the Houston area. ![]()
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