2013 Session: 397

• Learning from Eight Operational Diverging Diamond Interchangesin the United States
  Abstract: The Diverging Diamond Interchange (DDI) has quickly gained popularity across the United States due to its ability to improve traffic operations and safety with significant cost savings. As of August 2012, thirteen DDIs have been opened to traffic in the United States with the first one opening in July 2009 in Springfield, Missouri. Dozens more are either under construction or are in the final stages of design.The DDIs that have been constructed have many similar elements to the first Springfield DDI, but there are also many noticeable differences. This paper investigates a dozen different design elements of eight operational DDIs in the US and analyzes how those elements may affect the safety and/or operations of the interchange. The main goals of the research are to understand the operational effects of the different design elements within the DDI, separate theory and antidotal evidence from reality and science, and prioritize the important elements within the DDI. The biggest lesson learned from these operational DDIs is that there needs to be a greater emphasis on sight distance in the design. This relates to viewing signs and signal heads properly. It also relates to decision, stopping, and intersection sight distance issues. Other lessons learned include using signing and striping properly, giving drivers clear guidance, and that there are several acceptable ways to design elements within the DDI as long as there is an attention to detail.
  Authors: Chlewicki, Gilbert
  Authors: Chlewicki, Gilbert
  Year: 2013
  Document Type: Paper
  Subject: Operations and Traffic Management
  Session: 397
  Paper Number: 13-4023
• Left-Turn Lane Maneuver Length
  Abstract: In order to observe the point where vehicles entered a two-way left-turn lane (TWLTL) prior to turning left into a driveway, data were collected in the vicinity of ten unsignalized driveway connections along relatively level roadways with four through lanes. All of these driveways served commercial tracts. The connections were at least 500 ft from the nearest signalized intersection. At four of the sites, the posted speed limit was 35 mph, and at six sites it was 40 mph. For each vehicle, the observer noted whether the lane change was made at a time in which the traffic state in the TWLTL could be categorized as having a standing queue, moving queue, or no queue. The distributions of the distances at which vehicles shifted into the TWLTLs were found separately for the 35 mph and the 40 mph groups, and adjustments were made for the lengths of any queues present. From this, one can infer, for various percentiles of all vehicles entering the left-turn lane, the distance in advance of a connection at which the lane changing maneuver takes place. Knowing the distance in advance of a driveway connection at which unconstrained drivers choose to move from the through lane into the left-turn lane can help those modeling two-way left-turn lanes (TWLTL) in simulation programs, specifying the separation between two successive connections on opposite sides of the roadway, or designing left-turn lanes on roadways with restrictive medians. To these distances, one must also add the length of any standing queues waiting to turn left.
  Authors: Gattis, J. L.; Frierson, Tymli A.; Duncan, Lynette K.
  Authors: Gattis, J. L.; Frierson, Tymli A.; Duncan, Lynette K.
  Year: 2013
  Document Type: Paper
  Subject: Operations and Traffic Management
  Session: 397
  Paper Number: 13-4428
• Safety Effects of Cross-Section Design on Urban and Suburban Roads
  Abstract: Understanding the safety effects of cross section allocation on urban and suburban roads is important for agencies implementing complete streets philosophies. Research on urban and suburban arterials, conducted as part of Highway Safety Manual development, found no consistent relationships between lane width and safety. Other studies indicated that urban streets with lanes narrower than 12 feet are not less safe, and may even be safer, than those with 12 foot and wider lanes. These studies addressed geometric elements in isolation, potentially leading to the inconsistent and counterintuitive findings. This paper takes a new look at the safety effects of cross section allocation on urban and suburban road segments. The effects of cross section element combinations and interactions, with a specific focus on lane width, shoulder width, and shoulder type, are considered as an inherent part of model estimation. The dataset for this study includes 1,577 urban street segments in Illinois, totaling nearly 380 miles in length. Three years of crash data were used for model estimation. Results show interactions between lane width and shoulder width that would not have been uncovered if these elements were considered in isolation. Shoulder width has a larger effect on safety when lanes are narrow and this safety effect decreases as lane width increases. Wider lanes do not always result in an increase in safety, particularly when shoulders are wider. Crash modification factors for cross section design element combinations were developed using modeling results. Safety performance functions for urban and suburban road segments are also presented.
  Authors: Le, Thanh Q.; Porter, Richard Jon
  Authors: Le, Thanh Q.; Porter, Richard Jon
  Year: 2013
  Document Type: Paper
  Subject: Operations and Traffic Management
  Session: 397
  Paper Number: 13-5120
• Considering and Applying Driveway Design for All Users
  Abstract: NCHRP Project 15-35, Geometric Design of Driveways, was initiated to help address the lack of current comprehensive research and national design guidance for the design of driveway connections to roadways. The research initiated with this project included an extensive literature review, a survey of state agencies and contacts with interest groups, and field work to measure traffic attributes. The project produced two publications, a research report on the NCHRP website and the Guide for the Geometric Design of Driveways, NCHRP Report 659. This paper considers the following topics.* What design issues were identified? Current design practices may not adequately consider the range of all driveway users – bicyclists, motorists, and pedestrians. This section will also report vulnerability of various users, based on historic crash data.* What user attributes were found? The research conducted produced information about the driveway grades at which the undersides of vehicles may drag, and the speeds at which vehicles on urban arterials entered commercial driveways having radii ranging from 13 to 20 ft. * What design practices were recommended? To address the needs of all users, the design guide offered a number of design applications that differ from commonly-seen practices.This paper provides useful information for design consultants and local government professionals.
  Authors: Gattis, J. L.; Gluck, Jerome Steven; Barlow, Janet M.; Eck, Ronald W.; Hecker, William F.; Levinson, Herbert S.
  Authors: Gattis, J. L.; Gluck, Jerome Steven; Barlow, Janet M.; Eck, Ronald W.; Hecker, William F.; Levinson, Herbert S.
  Year: 2013
  Document Type: Paper
  Subject: Operations and Traffic Management
  Session: 397
  Paper Number: 13-2223
  Practice-Ready: Yes
• Considering and Applying Driveway Design for All Users
  Authors: Gattis, J.
  Authors: Gattis, J.
  Year: 2013
  Document Type: Presentation; Poster
  Subject: Operations and Traffic Management
  Session: 397
  Paper Number: 13-2223
• Learning from Eight Operational Diverging Diamond Interchanges in the United States
  Authors: Chlewicki, Gilbert
  Authors: Chlewicki, Gilbert
  Year: 2013
  Document Type: Presentation; Poster
  Subject: Operations and Traffic Management
  Session: 397
  Paper Number: 13-4023
• Left-Turn Lane Maneuver Length
  Authors: Gattis, J.
  Authors: Gattis, J.
  Year: 2013
  Document Type: Presentation; Poster
  Subject: Operations and Traffic Management
  Session: 397
  Paper Number: 13-4428
• Achieving Access Management Success Through Stakeholder Involvement on Highway 101
  Authors: Chromy, Chris
  Authors: Chromy, Chris
  Year: 2013
  Document Type: Presentation; Poster
  Subject: Operations and Traffic Management
  Session: 397
  Paper Number: P13-6398
• Before-and-After Study of Effectiveness of Rectangular Rapid-Flashing Beacons Used with School Sign in Garland, Texas
  Authors: Brewer, Marcus
  Authors: Brewer, Marcus
  Year: 2013
  Document Type: Presentation; Poster
  Subject: Operations and Traffic Management
  Session: 397
  Paper Number: P13-6397