Addressing Bottlenecks
Bottlenecks have been the focus of transportation improvements – and of travelers' concerns – for many years. On much of the urban highway system, there are specific points that are notorious for causing congestion on a daily basis. These locations – which can be a single interchange (usually freeway-to-freeway), a series of closely spaced interchanges, or lane drops – are focal points for congestion in corridors. Major bottlenecks tend to dominate congestion in corridors where they exist.
Many bottlenecks acquire nicknames from local motorists such as:
- "Spaghetti Bowl" in Las Vegas;
- "Hillside Strangler" in Chicago;
- "Spaghetti Junction" in Atlanta; and
- "Mixmaster" in Dallas.
Solving Recurring Bottlenecks is a Win-Win Situation for Nonrecurring Incidents Too! The result of improving a recurring bottleneck location is to provide additional base capacity. Up to 60 percent of all congestion is nonrecurring; i.e., related to events such as accidents, weather, and work zones, etc. Improving base capacity by addressing recurring bottleneck locations will also benefit nonrecurring events. The capacity loss resulting from the nonrecurring events will be lessened due to the improvements made to the system to benefit the recurring situation. |
In the past several years, transportation professionals have come to realize that highway bottlenecks demand special attention. Several national studies have highlighted bottlenecks as a major congestion problem in urban areas. These studies have raised the level of awareness about bottlenecks as a problem, warranting that they be treated as a significant part of the congestion problem.
The American Highway Users Alliance (AHUA) conducted two studies of the Nation's urban bottlenecks in 1999 and 2004. The studies produced rankings of the worst bottlenecks in terms of total delay to travelers and discussed what was being done to fix the problems, where specific improvements had been scheduled. The studies found that nearly all of the worst bottlenecks are major freeway-to-freeway interchanges in large urban areas. The 2004 study updated the rankings and discussed three bottleneck improvement "success stories" – bottlenecks identified in 1999 that were now improved or well under construction.
FHWA's first effort related to bottlenecks was in the freight (trucking) arena. Using the AHUA studies as a starting point, the impact of bottlenecks on truck travel was assessed. Bottlenecks outside of urban areas also were considered (e.g., steep grades). A major finding of this study was that in terms of total delay, the urban bottlenecks – typically thought of as commuter related – also are the major sources of truck delay.
States and regions are beginning to recognize the significance of bottlenecks as well. The Ohio Department of Transportation completed a study of freight (trucking) bottlenecks and the Interstate-95 Corridor Coalition is undertaking a study of all potential bottlenecks in Coalition states. The Atlanta Regional Commission has defined bottlenecks as a specific portion of their Congestion Management Process and is identifying regional and local bottlenecks in their network.
Table 2. The Worst Physical Bottlenecks in the United States 2002
| Rank | City | Freeway | Location | Annual Hours of Delay Hours (in Thousands) |
|---|---|---|---|---|
| 1 | Los Angeles | U.S. 101 | U.S.-101 (Ventura Freeway) at I-405 Interchange | 27,144 |
| 2 | Houston | I-610 | I-610 at I-10 Interchange (West) | 25,181 |
| 3 | Chicago | I-90 | I-90/94 at I-290 Interchange ("Circle Interchange") | 25,068 |
| 4 | Phoenix | I-10 | I-10 at SR-51/SR-202 Interchange ("Mini-Stack") | 22,805 |
| 5 | Los Angeles | I-405 | I-405 (San Diego Freeway) at I-10 Interchange | 22,792 |
| 6 | Atlanta | I-75 | I-75 south of the I-85 Interchange | 21,045 |
| 7 | Washington (D.C.-Maryland-Virginia) |
I-495 | I-495 at I-270 Interchange | 19,429 |
| 8 | Los Angeles | I-10 | I-10 (Santa Monica Freeway) at I-5 Interchange | 18,606 |
| 9 | Los Angeles | I-405 | I-405 (San Diego Freeway) at I-605 Interchange | 18,606 |
| 10 | Atlanta | I-285 | I-285 at I-85 Interchange ("Spaghetti Junction") | 17,072 |
| 11 | Chicago | I-94 | I-94 (Dan Ryan Expressway) at I-90 Skyway Split (Southside) |
16,713 |
| 12 | Phoenix | I-17 | I-17 (Black Canyon Freeway) at I-10 Interchange (the "Stack") to Cactus Road |
16,310 |
| 13 | Los Angeles | I-5 | I-5 (Santa Ana Freeway) at SR-22/SR-57 Interchange ("Orange Crush") |
16,304 |
| 14 | Providence | I-95 | I-95 at I-195 Interchange | 15,340 |
| 15 | Washington (D.C. Maryland-Virginia) |
I-495 | I-495 at I-95 Interchange | 15,035 |
Source: Unclogging America's Arteries: Effective Relief for Highway Bottlenecks, American Highway Users Alliance, February 2004. Only those bottlenecks that cause an estimated 10 million hours of annual delay are included in this list.
