Examples of How Agencies Are Dealing with Bottlenecks
Many transportation agencies have recognized that low-cost treatments can provide effective congestion relief at bottlenecks. A wide variety of improvements have been implemented and many innovative improvements are emerging. This section provides a snapshot of how transportation agencies are using these strategies to improve congestion at bottlenecks, including:
- Washington State's integrated operations/construction programs;
- Addressing a truck-related bottleneck in Washington State;
- Florida's treatment at an interchange weaving area;
- Maryland's treatment at an interchange bottleneck;
- Low-cost bottleneck improvements in Texas; and
- Georgia DOT's low-cost efforts to improve the Atlanta Downtown Connector.
Washington State Department of Transportation's Integrated Operations/Construction Programs in the Puget Sound Region and Seattle The Washington State Department of Transportation has used freeway ramp meters in the Puget Sound system for two decades. By providing a regular flow of traffic and lower entering volumes at busy entrance ramps, the meters allow the freeway mainline to carry more volume and at higher speeds. In addition, the greater spacing between entering vehicles has resulted in 30 percent fewer rear-end and sideswipe collisions and lower travel delay. I-405 and SR 167 are major commuter routes in the south Puget Sound area. A $10 million project to add a new exit ramp from I-405 to southbound SR 167 reduced the stop-and-go traffic from a nearly two-mile backup to less than one-half mile and increased the traffic volumes handled on the ramp by 8 percent and the mainline by 13 percent. Other minor capacity improvements also have been key to maximizing the returns from the roadway investments. The addition of a "weaving-lane" between an entrance ramp and exit ramp allows merging and exiting traffic to move more smoothly to their destinations. Where traffic patterns have changed since the initial road construction, a short section of additional travel lane can allow a bottleneck to be relieved and provide a technique that uses road capacity more efficiently. |
Addressing a Truck-Related Bottleneck in Washington State The Puget Sound region in Washington is a place of high truck activity because of the burgeoning international port business. SR 167 in Federal Way exhibited a bottleneck caused by a steep grade that dramatically reducing truck speeds. An additional lane was added on this grade to accommodate slow moving trucks. |
Florida Solves Interchange-Related Weaving Problem in Tampa The interchange of I-75 and Bruce B. Downs Boulevard in suburban Tampa exhibited the characteristics of a bottleneck amenable to a low-cost improvement. One of the major traffic flows is a right turn from the ramp and a quick left turn onto an arterial. The weaving on the cross street caused queuing on the ramp which often backed up to the freeway mainline. The problem was addressed by adding a free right turn lane and a signalized right turn lane. The traffic that needed to make the quick left turn is signed to use the signalized right turn lane. Queuing on the mainline is no longer a problem. |
Maryland's Quick Fix at Interstate-70/Intestate-695 A recent project at the I-70/I-695 (Baltimore Beltway) interchange outside of Baltimore was discussed. The eastbound approach from I-70 to I-695 backed up on to the mainline of I-70, restricting through traffic. Widening the entire ramp would have been very expensive due to the need for major bridge reconstruction. Instead the ramp was widened up to the bridge. This provided adequate storage to relieve the backup on to the mainline and did so at a reasonable cost. |
Low-Cost Bottleneck Improvements in Texas. The Texas Department of Transportation (TxDOT) has undertaken significant low-cost freeway bottleneck improvements in recent years. These include:
Source: Walters, Carol H, Cooner, Scott A., and Ranft, Stephen E., Looking Again at Bottlenecks on Freeways Evaluating Case Studies in Texas, November 15, 2004, http://pubsindex.trb.org/document/view/default.asp?lbid=775977. |
Georgia DOT's Low-Cost Efforts to Improve the Atlanta Downtown Connector Georgia DOT has attempted to enhance the I-75/I-85 operations in the past few years. The Downtown Connector is a four-mile section of freeway between the I-75/I-85 merge just north of downtown (Brookwood Interchange) to I-20. It was identified as the nation’s sixth worse bottleneck in the 2004 American Highway Users Alliance Bottleneck study. In late 2003 Georgia DOT re-striped and extended a divider wall to add ramp storage and reduce weaving at three ramps: North Avenue and 10th northbound and Ellis Street southbound. In April 2005 GDOT installed four southbound entrance ramp meters in that section (at Spring Street, Ellis Street, Freedom Parkway, and Edgewood Avenue). The ramp meters saved a weekly average of 17.3 percent in fuel and 22.4 percent in time for the four-hour p.m. peak. Between 2004 and 2005 the number of severe congestion hours was reduced by 37.7 percent. Two Photos of the Interstate-75/Interstate-85 Bottleneck (Locally Known as the Downtown Connector) in Atlanta, Georgia in the p.m. Peak-Period
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