Cover Image

Not for Sale



View/Hide Left Panel
Click for next page ( 12


The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement



Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 11
11 the study results suggest a trend toward ramp metering as a cient clearing of accidents and restoration of vehicle movement low-cost bottleneck improvement (12). The practice is said to along roadways. Dunn and Latoski (16) also offered several both decrease delay and to decrease the number and severity low-cost, training-based examples of traffic incident manage- of crashes (thus decreasing traffic incident delay). To assess ment enhancements, including: the benefits and costs of ramp metering, Minnesota DOT con- ducted a test of the effectiveness of the system that is deployed Integrating private towing and recovery companies into in the Twin Cities region. Several of the ramp meters were training programs turned off during this experiment, and increases in delay, along Training approaches such as video and stakeholder-specific with decreases in safety, were the end result; it was determined instructional presentations through this study that use of ramp metering in the Twin Cities Incident management response team debriefings to identify saves $40 million annually (15). The greatest benefits of such lessons learned. a system for the trucking industry are likely found on trips through urban areas, where trucks would face fewer and less Traveler information is available in several forms (e.g., severe bottlenecks caused by vehicles that are entering the changeable electronic message signs, radio broadcasts, 511). highway. Commercial motor vehicle operators may have additional Interviews of state and local transportation agencies (8, 12) sources of information as well, including the support received showed that the addition of auxiliary lanes ranked second through dispatchers and other trucking operations personnel, among participants, and is listed as a good solution to the as well as through communications with other truck drivers following issues: (e.g., over CB radio or cell phone). FHWA (17) identified several types of information that can Heavy on-ramp demand be disseminated to travelers in order to decrease congestion Lane drops in certain areas, including: Horizontal/vertical curves Inadequate accelerated and/or decelerated lanes. Weather information Variable speed limit signs The Government Accountability Office (GAO) (5) suggests Information related to roadway diversions, alternative that "limited parking for delivery to be received adds delay" to routes, emergency evacuations, and construction. freight movement. It can be inferred from this statement that a low-cost method of increasing freight mobility/efficiency at Systems such as 511 and electronic message signs can pro- the point of delivery is therefore to remove automobile park- vide details on traffic incidents and travel times. Whether or ing and/or designate freight delivery parking areas. not to categorize such activities as low cost is debatable. In a Changes to the characteristics of signals are also discussed large metropolitan area, for instance, the initial cost of a 511 in the literature. Low-cost improvements to traffic signals to system is estimated to be over $40 million, with annual costs prevent crashes (and subsequently increase mobility) include: of approximately $2.5 million (18). Finally, work zone management techniques can have an All-red intervals impact on freight mobility issues related to highway construc- Installation of 12-inch signal heads (increased from 8-inch) tion. As an example, work zone management software, week- Installation of additional signal heads at a different level end and night construction, and incentives for early comple- (e.g., post mounted) tion can successfully decrease the time in which a section of Changing location of traffic signals, or adding back plates roadway is disrupted (19). to increase visibility (10). 2.2.5 Examples of Low-Cost Signal improvements have been successfully used to increase Operational Improvements the efficiency of left turns in Maryland. At an approximate cost of $5,000 per improvement, the state has implemented the Georgia DOT's Low-Cost Efforts to Improve the Atlanta following improvement types: Downtown Connector--In this example, low-cost im- provements were implemented to reduce delay and improve Two turn phases per cycle mobility on a 4-mile section of downtown freeway con- Half-cycle variation nector in Atlanta, Georgia. The improvements include re- Directional lead-lag (10). striping and extension of a divider wall to add ramp storage and reduce weaving at three ramps and installation of GAO (5) found that traffic incident management programs four southbound entrance ramp meters in that section. The have the ability to increase freight mobility through the effi- result was that the ramp meters saved a weekly average of