Managing Managed Lanes
Supporting Technologies and Strategies
Managed lanes require management, which in turn requires the application of advanced technologies and strategies to optimize system operations. Some strategies and technologies have been applied widely, including in northeastern Illinois. Some of the strategies discussed for managed lanes are experimental.
Management of a managed lane facility is usually coordinated through a traffic operations center, which is the nexus of a Transportation communications system linking highway data (sensors indicating volumes and speeds, audio-video feeds, and traffic control device status data) with control features (dispatch of emergency and incident personnel, ramp meter controls, and traveler information provided through expressway variable message signs, broadcast and Web-based information services). A key control strategy for traffic management centers is the detection and quick removal of incidents. Future advancements, through an integrated corridor management system, could integrate freeway and arterials with arterial variable message signs, traffic signal control, and access controls. Integration would facilitate a system-wide response to serious incidents, while likewise facilitating alternative routes through signal and access controls.
A second control strategy employed by traffic operations centers to manage lanes is to smooth the flow of vehicles to prevent incidents and optimize travel speeds. To smooth traffic flow, traffic operations centers can control ramp meters, close access points, and could, with appropriate authority, establish speed and lane control regulations. For example, speed management establishes speed limits or speed guidance in real time to ramp down speeds slowly as traffic approaches slower speeds ahead. Such a system prevents crashes, maximizes throughput, and reduces shock-wave effects of stop-and-go traffic resulting from incidents and bottlenecks.
For dynamic pricing applications, highway information explained above is used to establish the price at which the established performance measure (e.g., maximum hourly volumes and minimum speeds) is maintained and sustainable. The established price is then transmitted to toll notices on the highway, the corridor, and through information services, allowing travelers to make route and mode choices in real time.
Establishing Performance Standards
Two meaningful and highly interrelated sets of performance measures can be used by system operators to assess and maintain managed lane effectiveness:
Traffic Speed and Volume
Levels can be used to measure performance, in some cases on a real time basis. However, these are often derivative measures of in-pavement loop detectors that measure lane occupancy rates. Other detection strategies include microwave, infrared, and video sensors that each have strengths and weaknesses.
Travel Time is perhaps the truest measure of value to drivers, but can also be the most difficult to measure. One process uses existing corridor speed/volume sensors to calculate travel time. Also, travel times can be collected from transponder-equipped vehicles by matching transponder identification numbers at two points. However, these processes result in a lag time between the measurement and its dissemination to drivers based on the time that it takes a transponder-equipped vehicle to travel the distance. Adjustments are feasible to account for upstream and downstream volume, time of day, and other stochastic processes.
Figure 4 (top) and Figure 5 (bottom)
Access to managed lane facilities is guided by optimizing system performance. Caltrans seeks to maintain traffic conditions on the San Diego's I-15 Express Lanes at an LOS of level "C" which is generally a Volume to Capacity ratio of .66 to .80. Volume over Capacity or V/C as seen in Figures 4 and 5 (above) can be broken down into a flow rate, or throughput, usually in vehicles per hour per lane (VPHPL). Most expressway systems are built for a maximum capacity of 2000-2200 VPHPL.This measure generally occurs at a travel speed no more than 10 mph lower than free-flow speed. Beyond the maximum capacity systems break down resulting in lower travel speeds and lower volumes. 1700 VPHPL is a standard flow threshold cited by several managed lane system operators. Figures 6 and 7 (below) chart the positive effects on vehicle speed and throughput of congestion pricing strategy as applied along California's State Route 91. Several additional performance measures (Congestion Measures) are listed on a corridor data sheet for Denver's Wadsworth Boulevard, see Table 3 (below).
Figure 6 (left) and Figure 7 (right)
Other measures of managed lane strategy performance include vehicle and person throughput, particularly for peak periods. HOV lane systems have had notable success in achieving high levels of person throughput relative to vehicle throughput. In 2007, the Seattle region's extensive HOV network moved 34% of all travelers on 19% of the vehicles traveling daily. By moving more people with fewer vehicles, these HOV lanes, like many other HOV lanes, have been able to maintain speed and travel time advantages over general-purpose lanes (Downs, 2004. p. 110).
Regional Performance Measurement: Highway Traffic Safety Data Overview
2011 Performance Measure Update
Following are updated regional traffic safety performance measures. Through 2011, the measures show substantial improvement since 2002, though regional fatalities rose slightly from 2009 to 2010. In addition to the summary table below, details for Chicago, suburban Cook County, and the collar counties and by pedestrians and cyclists are available in detailed tables.
|Fatalities per 100 Million VMT||1.15||1.04||0.74||0.67||0.68||0.65|
|Fatalities per 100 Thousand Population||8.19||7.59||5.24||4.69||4.72||4.38|
|Non-Fatal Injuries per 100 Million VMT||146||124||105||99||99||99|
|Non-Fatal Injuries per 100 Thousand Population||1,041||906||739||697||691||664|
|PDO Reporting Threshold||$500 minimum reporting threshold for crashes with property damage only||$1500 minimum reporting threshold for crashes with property damage only|
|Motor Vehicle Crashes||310,001||297,322||284,877||198,639||194,534||191,744|
|Motor Vehicle Crashes per 100 Million VMT||526||491||482||336||331||336|
|Motor Vehicle Crashes per 100 Thousand Population||3,761||3,590||3,407||2,364||2,307||2,263|
Sources: Calculated by CMAP based on IDOT and US Census Bureau data.
Note: The reporting threshold for crashes with property damage only changed in 2009. The result was a reduction in the number of crashes included in IDOT's crash databases for 2009 and subsequent years. The sharp reduction shown above from 2008 to 2009 doesn't indicate an actual improvement in highway safety.
2008 Archival Report: Highway Traffic Safety Data Overview for Metropolitan Chicago. This analysis, as reported by Jon Hilkevitch's Getting Around column in the Chicago Tribune, provided an overview of highway traffic safety trends in the Chicago region. The report, like the data above, showed substantial reductions in fatalities and serious injuries since 2002.
The causes of motor vehicle crashes are complex, owing to interactions between vehicles, roadways, and driver behavior. However, the report demonstrates that concerted efforts to improve vehicles' ability to avoid crashes, vehicles' crashworthiness, driver training and compliance with traffic safety laws, and highway safety engineering focused on addressing locations with high rates of fatal and serious injury crashes have, together, had a strong positive effect over the past several years. In addition, faster detection of crashes and faster response by emergency personnel may have also had a role in making regional crashes less deadly.
Supplementary Information: Highway Safety Improvement Strategies:
To address highway safety, communities and highway agencies have engaged in a number of strategies to reduce crashes. Implementation of some strategies is just beginning, or may even be experimental, while other strategies may be fully implemented. A definitive Highway Safety Manual has been published by the American Association of State Highway and Transportation Officials (see item below). Here are a few resources on improving highway safety, including information on proven strategies. Note that the implementation of all strategies is subject to further study of a particular proposed improvment site, evaluation of detailed crash information, and engineering judgment. Various vendors and technologies to implement the strategies may have specific strengths and weaknesses that must be evaluated by implementing agencies. Further, none of the strategies is a substitute for traveling with care while on the road, and taking necessary precautions like wearing a safety belt and avoiding driver distractions.
- Revised 2012: The Federal Highway Administration has prepared a web site on proven safety countermeasures and has released a revised Guidance Memorandum on Consideration and Implementation of Proven Safety Countermeasures: This policy document provides a brief analysis of nine proven safety countermeasures, indicating when and where these countermeasures should be used. The countermeasures include safety edge, roundabouts, corridor access management, backplates with retroreflective borders, longitudinal rumble strips and stripes on 2-lane rural roads, enhanced delineation and friction for horizontal curves, medians and pedestrian refuge areas in urban and suburban areas, pedestrian hybrid beacons, and "road diets" (roadway configuration).
- Federal Highway Administration: FHWA Safety Program: In addition to the information above, FHWA maintains information related to its reseach, program support, and promotion of many strategies to address safety. These include intersection safety, local and rural road safety, pedestrian and bicycle safety, roadway departure safety, speed management, and additional initiatives.
As part of its strategy research for GO TO 2040, CMAP also studied the following strategies with positive implications for highway safety:
- Roundabouts (strategy paper) (see also the July, 2010 FHWA video on roundabouts, posted on the FHWA roundabout page).
- Access Management (strategy paper)
Of course, crashes are directly related to driving, and can be reduced by implementing proven travel demand management strategies (strategy paper). More broadly, implementing many of the recommendations of the draft GO TO 2040 Regional Comprehensive Plan will also reduce travel demand, by encouraging the development of more compact, walkable communities.
Motor Vehicle Crashes with Bicycles and Pedestrians
CMAP maintains a separate web page with data and maps related to walking and cycling safety. The data and maps are posted here.
Highway Safety Manual
The Highway Safety Manual (HSM) has been published by the American Association of State Highway and Transportation Officals (AASHTO) after a decade of research and analysis by AASHTO, the Federal Highway Administration, and the Transportation Research Board. The Manual will help measurably reduce the frequency and severity of crashes on roadways by providing tools for analyzing safety impacts in the during highway project development. The Manual will assist engineers and planners in selecting countermeasures and prioritizing projects, and comparing alternatives. For more information about the manual, see http://www.highwaysafetymanual.org/Pages/default.aspx. The manual is available to purchase from either AASHTO or the Institute of Transportation Engineers.
Community Safety Approach
CMAP strongly encourages northeastern Illinois to take a community approach to addressing highway safety that uses the best data and analysis combined with local knowledge of traffic conditions to reduce crashes. This approach can result in safety improvements by strategically looking at traffic patterns in a corridor or neighborhood to address traffic crashes, identifying ways not only to reduce crash risk, but the exposure to risk as well. Sometimes, a solution to a crash problem at one location may be a few blocks or more away.
Presentation to Council of Mayors (pdf, 1MB) February 5, 2008
Detailed Analyses for Engineers and Planners
Intersection Crash Analyses
Intersection Crash Analyses, Years 2005-2006. (Revised December 22, 2008) This report examines high-crash locations in 2005-2006 in metropolitan Chicago that contain intersections. The goal of the report is to identify intersections that have high crash frequencies or high crash rates for specific types of crashes. Determining where specific types of collisions occur will allow safety funds to be invested where they may be of the highest benefit.
Regional Crash Maps
The maps below are technical maps of crash locations and crash concentrations within Metropolitan Chicago. These data represent one among many resources that may be used by engineers and planners to identify sites that might bear further analysis of crash information. The data are not definitive in identifying hazards, since they do not control for volumes at intersections or highway segments. Furthermore, any hazard identification should include a review of original crash records by professional personnel. However, the crash data may be an information tool to use to begin a community process of improving highway safety where concentrations of crashes and casualties are identified.
The most serious cost of crashes is the human toll in casualties - injuries and deaths. Thus, most of the maps below are focused on identifying the sites of fatalities and serious injuries. However, less serious crashes also have a price in property damage and delay. Therefore, that information is also available (via our ftp site because of the file size).
Instructions for using these maps are provided and should be read before trying to open the maps. The maps are technical in nature, with many layers that can be opened and closed, and are best used at highly zoomed-in levels (800-2400%).
Map of All Regional Crashes
A regional map of all crashes in 2005-2006 (pdf, 46MB) is posted to the CMAP FTP site. Access the map with username "cmapftpro" and password "cmapread". Right-click on the posted file entitled safety_allcrashes_yrs0506_20080208.pdf, then select "Save As" to your computer. Note: The map includes several hundred thousand crashes, so opening this file takes some time on even fast computers.