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28 CHAPTER 4: WEB-BASED SURVEY This chapter summarizes the results from a web-based survey that was conducted to identify the location of signalized intersections with ATLs across the United States and to gather information, data, and experiences of agency staff on the performance of ATLs. The online survey included the following features: ⢠Examples of different types of ATL configurations; ⢠A Google Maps interface that allowed respondents to geographically locate an ATL site by âpinningâ it on the interactive map; and ⢠A download tool to automatically export the raw survey results into an Excel spreadsheet along with longitude/latitude data for each identified ATL. The survey was distributed through the American Association of State Highway and Transportation Officials (AASHTO) Subcommittee on Traffic Engineering (SCOTE), AASHTO Standing Committee on Research (SCOR) Research Advisory Committee (RAC), and Transportation Research Board (TRB) committees. Figure 10 shows a screen capture from the website interface and Table 7 identifies the questions asked in the survey. Figure 10. Survey website interface.
29 Table 7. Survey questionnaire. Question Options 1 Do you know of intersections with ATLs that fall into any of the categories listed to the right of this survey? Yes / No 2 Type your intersection and city/state in the text box below or use the map to browse and select the intersection. Pin on the Google Map 3 Which type of ATL does this intersection have, had, or is potentially going to have? Primary Type A Related Type B Related Type C Related Type D Other / Hybrid 4 Which category does this intersection fall into? Built and operational Planned but not yet built Studied but not chosen for implementation Previously existing but since removed Under Review Other 5 Please indicate whether any of the following data for this intersection are available and could be shared with the research team: Traffic Counts Yes / No / Maybe Crash Data Yes / No / Maybe Signal Timing Yes / No / Maybe Speed Information Yes / No / Maybe Previous Study Yes / No / Maybe Anecdotal Evidence Yes / No / Maybe Other Information Yes / No / Maybe 6 If you answered yes to any part of question 5, who may we contact regarding details of this evaluation? Me Other (provide contact information) 7 Does your organization have written analysis or design guidelines regarding the use and evaluation of ATLs? Yes / No 8 Is there anything else you would like to share with the research team regarding ATLs? (open) A total of 42 out of 249 transportation agency contacts responded to the survey resulting in a response rate of 17%. Table 1 summarizes the number of ATL approaches identified from the survey respondents. Note that a single intersection can include one or more ATLs.
30 Table 8. Summary survey statistics. Metric Count Total ATLs 144 Total Intersections with ATLs 117 Number of States with identified ATLs 22 Number of ATL configuration types 11 As shown in the exhibit, a total of 144 ATLs were identified in the survey across 117 intersections in 22 states of the United States. Figure 11 displays the identified ATL locations geographically. These locations provided the basis for determining the field data collection sites. The remainder of this chapter presents findings from the survey organized by the following topics: ⢠Organization type of respondents ⢠Region ⢠Upstream and downstream ATL configuration ⢠Right-turn treatment ⢠Number of continuous through lanes ⢠Surrounding land use ⢠Available traffic and safety data ⢠Anecdotal comments ORGANIZATION TYPE The survey respondents represent state departments of transportation (DOT), counties, cities, universities, and consultants. Respondents from the academic and private sector generally provided a public agency contact. Figure 12 displays the number of respondents by agency type for all 42 participants.
31 Figure 11. Map of the ATL sites in the United States. 5 5 29 2 1 0 5 10 15 20 25 30 35 City County DOT University Consultant Agency Type Figure 12. Respondents by agency type. REGIONAL LOCATIONS Sites were identified in all regions of the US. Figure 13 shows the number of ATL approaches by region as categorized by: Midwest (MW), Northeast, (NE), Northwest (NW), Southeast (SE) and Southwest (SW).
32 2 32 2 16 2 1 20 15 3 5 19 3 4 1 2 1 1 31 3 6 0 5 10 15 20 25 30 35 40 MW NE NW SE SW AUS New Jersey Queensland Indiana North Carolina Tenessee South Carolina Ohio West Virginia Washington Utah Oregon New York Nebraska Missouri Maryland Louisiana Idaho Florida Connecticut California Arizona Count of Approach ID Region of Country State Figure 13. Count of sites by region of the United States. The number of sites by region is relatively balanced, with the highest number identified in the southwest (led by California) and the second highest number of sites in the northeast (led by Maryland). UPSTREAM AND DOWNSTREAM CONFIGURATION Each ATL site has one of three possible types of upstream configurations: ⢠Continuous through lane (CTL): the auxiliary lane directly originates from an upstream through lane at least 1,250 feet from the intersection. ⢠Add lane: one lane is added to the continuous through lane(s) by widening the roadway width. ⢠Turn lane: the auxiliary lane begins from multiple left-turn or right-turn lanes on the side street. On the receiving end, ATL sites were classified based on one of four configuration/transition types: ⢠Right-hand merge: a reduction in the roadway width that tapers from the right-side of the roadway. ⢠Left-hand merge: a reduction in the roadway width that tapers from the left-side of the roadway. ⢠Right-hand drop: the ATL turns into a turn-only lane on the right-side of the roadway downstream of the intersection (trap lane).
33 ⢠Left-hand drop: the ATL turns into a turn-only lane on the left-side of the roadway downstream of the intersection (trap lane). Table 9 presents the proportion of the different downstream transitions per ATL upstream transition types. Table 9. Types of ATL by upstream and downstream transitions. Upstream transition Downstream transition LH drop LH merge RH drop RH merge Side-street multiple turn lanes 0 (0%) 1 (1%) 7 (5%) 12 (9%) Through add 3 (2%) 1 (1%) 9 (6%) 63 (45%) Through basic 1 (1%) 5 (4%) 15 (11%) 24 (16%) TOTAL 4 (3%) 7 (5%) 31 (22%) 99 (70%) The majority of the site approaches represents a conventional lane merge from the right originating from an added through lane (45%). Two other common types of auxiliary lanes are the ATL originating from a continuous through lanes that either merge from the right (16%) or are trapped as a right-turn lane (11%). Finally multiple turn lanes from the side street that merge from the right (9%) and added through lanes that drop as a right-turn only lane (6%) are less common. The other types of auxiliary lanes are rare. RIGHT-TURN TREATMENT From the literature search, the configuration and presence of a right-turn lane has a significant effect on lane utilization. Various types of right-turn treatments were identified. The right-turn treatment could be a short pocket (approximately 50 feet of storage), channelized island (protects right-turn movements at the intersection), pocket and channelized island, shared with a through lane, or none (T intersection). Figure 14 shows the proportion of the different types of right-turn lanes for the ATL approaches identified in the survey.
34 0 20 40 60 80 Shared ThRT + RT pocket 1 1 Shared ThRT 36 14 RT pocket/channelized 3 3 RT pocket 19 14 RT channelized 8 8 No RT 9 5 Th add Th basic Count of Approach ID Upstream transition Upstream right turn type Figure 14. Right-turn lane treatment by upstream transition. The majority of the ATL sites from the survey have either a shared through/right lane (50 sites) or an exclusive right-turn-pocket lane (33 sites). NUMBER OF CONTINUOUS THROUGH LANES The number of continuous through lanes on the approach for each of the ATL sites ranges from 1 to 4, and the number of downstream basic lanes ranges from 1 to 3. Table 10 provides a breakdown of sites based on the number of upstream and downstream basic lanes. This analysis was performed for through ATL sites (ATLs originating from side-street dual turns were not included). Table 10. Number of basic lanes on ATL approach (through only). Number of upstream continuous through lanes Number of downstream continuous through lanes 1 basic lane 2 basic lanes 3 basic lanes 1 basic lane 51 (42%) - - 2 basic lanes 29 (24%) 25 (21%) - 3 basic lanes 15 (12%) - 4 basic lanes - - 1 (1%) As shown in Table 10, the most common roadway approach type for the through ATL sites is one basic through lane upstream and one basic through lane downstream (42%). The second most common roadway approach type is two basic through lanes upstream and one basic through lane downstream, indicating that the ATL is used as a transition from a four-lane road to a two-lane road. Other roadway types include two basic lanes upstream and downstream, three basic lanes upstream and two downstream, and four basic lanes upstream and three basic lanes downstream.
35 LAND-USE/DEVELOPMENT TYPE The surrounding land-use and development type for each ATL site was classified based on a visual inspection of the surrounding area using aerial photography. Sites were classified as urban, suburban, or rural. Figure 15 summarizes the proportion of sites by land-use context. Rural, 37 Suburban, 58 Urban, 47Count of Approach Context Figure 15. Proportion of ATL approaches by context. The identified ATL approaches are located in a mix of rural, suburban, and urban contexts. The highest proportion of ATLs are located in suburban areas. TRAFFIC/SAFETY DATA AVAILABILITY Respondents were asked to indicate whether certain types of data are available for each ATL site. Figure 16 shows the answers, when positive, given by the respondents. 81 72 65 35 34 3 0 10 20 30 40 50 60 70 80 90 Signal Timing Data Trafic counts Crash Data Previous Study Speed Information Guidelines Yes Figure 16. ATL data types available as indicated by survey respondents.
36 Signal timing, traffic counts, and crash data are the most readily available data with respectively 57%, 50%, and 46% of all the ATL sites having this type of data. Previous studies and speed information are available for a lesser proportion of sites. Three agencies indicated that they have guidelines on the use of auxiliary through lanes: New York State DOT, Illinois DOT, and Caltrans. ANECDOTAL COMMENTS In addition, several respondents offered comments about their own experience with ATLs. Those are presented below: ⢠New Hampshire DOT. The intersection shown is one of dozens statewide at which traffic signals were added to a relatively high-volume highway and the ATLs were required to minimize delay. We do not have an inventory âof such instances but they are not uncommon. The most common complaint is that the merge following the intersection is too short or that aggressive drivers use the ATL to get ahead." ⢠Pima County, AZ. The Pima County/City of Tucson Pavement Marking Design Manual (Aug. 2008) has guidelines for signing and striping lane drops and trap lanes. ⢠Connecticut DOT. The contact person does not think any of these were specifically designed for the purpose of getting more vehicles through intersection and that they just got designed that way. ⢠Ada County, ID (no ATL sites). The contact person expressed concerns regarding types A and B, as they may gain capacity at the intersection, but merging back into few lanes downstream can present problems at higher traffic volumes. Types C and D are less of a concern, and are more common due to potential future widening of roads in developing areas. ⢠Mississippi DOT. Mississippi has intersections that use Type C and Type D elements. However, these were designed this way due to project geometric parameters/constraints and not specifically as an ATL project. ⢠Arkansas DOT. The only type of intersection that would approximate this design is at the end of a project where the widening is carried through the intersection in anticipation of another project. It would function as an ATL for a time until the adjoining project was constructed. ⢠Missouri DOT. Missouri found these to be mostly ineffective with local drivers. If they know the lane ends, they don't use it, so there is very little capacity benefit. ⢠Louisiana DOT. They tend to be underutilized by motorists who know the lane ends beyond the intersection, creating a lane imbalance in the next lane over. There is an issue of fairness at play here. However, the imbalance may contribute to improved performance of the adjacent right-turn-on-red maneuver. ⢠NYSDOT. The need and lengths of ATLs in NYS are determined based on crash data and traffic simulation software.
