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NCHRP 20-102(07) Interim Report 190 Appendix 4: DOT Traffic Control and Design Element Modifications Each state DOT provides guidance on roadway design and traffic control devices. The majority of states rely on the Federal Manual on Uniform Traffic Control Devices (MUTCD) for guidance on signs, markings, traffic signals, and other features to warn and/or guide traffic. Roadway design elements (i.e., geometric design features and criteria that guide the design of roadways) are typically addressed in design manuals.352 Design criteria are based on assumptions of vehicle speed, vehicle performance, and roadway conditions. Many of these criteria may be subject to change when the model design vehicle can be reasonably assumed to be level 3 and above C/ADS-equipped vehicles. We have assumed for this section that other Transportation Research Board/NCHRP studies will be looking at the specific technical elements of design criteria for the roadway network to accommodate level 4â5 ADS-equipped vehicles, possibly in conjunction with AASHTO and AAMVA studies that may be ongoing. However, we would highly recommend, that as part of the state audit, state DOTs also conduct a review of design manuals and other criteria used for highway design and traffic control. While most states have relatively strict sovereign immunity regarding liability for design and maintenance, suits may arise as level 4â5 ADS-equipped vehicles enter the transportation system, crashes inevitably occur, and alleged design defects are argued as the contributing factor. While this specific analysis has not delved into the complexities of state tort laws, analysis of 352 The States assessed in the following tables include Nevada, Nebraska, South Dakota, Wyoming, New Mexico, California, Texas, and Utah. Their respective roadway design manuals from which information in the tables below is cited are as follows: NV DOT Road Design Guide (2010), accessed from: https://www.nevadadot.com/doing-business/about-ndot/ndot- divisions/operations/traffic-information/road-design-guide NE DOT Roadway Design Manual (2017), accessed from: http://www.roads.nebraska.gov/business-center/design- consultant/rd-manuals/ SD DOT Road Design Manual (2017), accessed from: http://201sddot.com/business/design/forms/roaddesign/default.aspx WY DOT Road Design Manual (2015), accessed from: http://www.dot.state.wy.us/home/engineering_technical_programs/manuals_publications/road_design_manual.html NM DOT Design Manual (2016), accessed from: http://dot.state.nm.us/content/dam/nmdot/Infrastructure/DesignManual/NMDOT_Design_Manual.pdf CA DOT (Caltrans) Highway Design Manual (2014), accessed from: http://www.dot.ca.gov/hq/oppd/hdm/pdf/english/HDM_Complete_07Mar2014.pdf CA MUTCD (2014 Rev 2), accessed from: http://www.dot.ca.gov/trafficops/camutcd/camutcd2014rev2.html TX DOT Roadway Design Manual (2014), accessed from: http://onlinemanuals.txdot.gov/txdotmanuals/rdw/rdw.pdf UT DOT Roadway Design Manual of Instruction (2015), accessed from: https://www.udot.utah.gov/main/f?p=100:pg:0:::1:T,V:1498
NCHRP 20-102(07) Interim Report 191 this area by policy makers would be prudent to ensure that highway design and maintenance considers the level 4â5 ADS-equipped vehicle environment.353 The following section provides suggestions for potential modifications where state statute governs design criteria, and other recommendations for state DOTs as they review their design and maintenance manuals. The criteria can be loosely grouped into several categories, which are discussed below. Each category is supplemented with information in Table A14 through Table A19. General Design Considerations General design considerations are broadly applicable in how they influence vehicle operations, such as design speed and sight distance. These guidelines are typically applied in conjunction with vehicle code requirements for the establishment of posted speed limits. In most states, an engineering and traffic survey is conducted in order to determine the 85th percentile speed of typical roadway users on a typical day (e.g., no adverse weather conditions, outside of peak commute periods). These guidelines also apply industry standard metrics for operational performance (e.g., deceleration rates of vehicles and perception-reaction time of human drivers). With the. advent of C/ADSs, both the results of engineering and traffic surveys and the operational performance metrics used as the basis for design criteria could change substantially. (See Table A14.) Geometric Alignment Geometric alignment applies to both the horizontal and vertical planes, and concerns factors such as road curvature, grading, and superelevation. Similar to the general design considerations described above, state DOTs provide guidance for roadway design and operation based on assumptions of vehicle handling capabilities. As above, the advent of C/ADSs, the operational performance metrics used could change substantially. (See Table A15.) Geometric Cross Section Geometric cross section consists of design elements such as a lane and shoulder width, medians, and bicycle and pedestrian infrastructure. Geometric cross section requirements are typically provided to ensure consistency in design of roadways of various functional classifications. As C/ADSs may operate with greater control and safety, they may create an operating environment where lane widths and other geometric cross sectional features could be reduced. This could allow for additional space on roadways for other features, such as bike or transit lanes. However, 353 Kockelman et al (2016) for example, reviewed the implications of C/ADSs for the safety and operations of roadway networks, and detailed the types of C/ADS technologies, their major safety benefits and when TxDOT should become involved. A series of short, medium and long term strategies were recommended for TxDOT. See: Kara Kockelman, Paul Avery, Prateek Bansal, Stephen D. Boyles, Pavle Bujanovic, Tejas Choudhary, Lewis Clements, Gleb Domnenko, Dan Fagnant, John Helsel, Rebecca Hutchinson, Michael Levin, Jia Li, Tianxin Li, Lisa Loftus- Otway, Aqshems Nichols, Michele Simoni, and Duncan Stewart. Implications of Connected and Automated Vehicles on the Safety and Operations of Roadway Networks: A Final Report. October 2016. Accessed at: http://library.ctr.utexas.edu/ctr-publications/0-6849-1.pdf; and accompanying Best Practices Guidebook at: http://library.ctr.utexas.edu/ctr-publications/0-6849-p1.pdf
NCHRP 20-102(07) Interim Report 192 agencies should remain aware that at the local levels, some geometric design considerations are governed by emergency vehicle access requirements. Therefore, while C/ADSs may allow for reductions in geometric cross sectional requirements, emergency vehicle access requirements may take precedence. (See Table A16). Intersection and Interchange Design Intersection and interchange design includes issues of alignment, access ramp width, tapers, and spacing. State DOTs also provide guidance for intersection and interchange design based on assumptions of vehicle handling capabilities. With the advent of C/ADSs, the operational performance metrics used as the basis for design criteria could, again, change substantially. (See Table A17). Roadway Design Features Roadway design features are typically provided to ensure consistency in design of roadways of various functional classifications. Design features include road boundary elements, such as raised features, roadside barriers, and designs that demarcate the edges of vehicle right-of-way. As C/ADSs may operate with greater control and safety, roadway design features could be modified. This could allow for reduced roadside clearance requirements, which would have impacts on SAE J3016 level 0 vehicles and emergency vehicle access requirements. Therefore, while C/ADSs may allow for reductions in roadway design feature requirements, emergency vehicle level 0 vehicle requirements may still take precedence. (See Table A18). Road Signage and Traffic Control Road signage and traffic control communicates the rules of the road to drivers. The Federal MUTCD defines traffic control devices as âall signs, signals, markings, and other devices used to regulate, warn, or guide traffic, placed on, over, or adjacent to a street, highway, pedestrian facility, bikeway, or private road open to public travel by authority of a public agency or official having jurisdiction, or, in the case of a private road, by authority of the private owner or private official having jurisdiction.â 354 C/ADSs will dramatically change the needs and methods for regulating, warning, and/or guiding traffic. At the same time, level 0-2 vehicles will still require a wide variety of traffic control devices in order to ensure the safe and efficient movement for all roadway users. Therefore, DOT requirements related to traffic control devices will require special attention when being considered for modifications (See Table A19). Transportation Planning and Programming State DOTs may also want to consider how, in the long-term, to plan for, finance, and construct their transportation system as the C/AVS fleet grows in size, and engineering design decisions require dedicating specific funding for construction, reconstruction, and maintenance. Planning includes the consideration of pavement engineering elements that demarcate vehicle channelization, such as markings, striping, and rumble strips. Planning regulations here are also defined by federal statute in Title 23 of United States Code at Section 135 Statewide 354 Federal MUTCD; Introduction; pg I-1; https://mutcd.fhwa.dot.gov/pdfs/2009r1r2/r1r2covintrotoc.pdf
NCHRP 20-102(07) Interim Report 193 Transportation Planning and Section 134 Metropolitan Transportation Planning, and federal regulation at 23 CFR. The latter regulation sets out planning requirements that state DOTs (as well as Metropolitan Planning Organizations) must adhere to. In addition, 23 CFR sets out design standards to be used for federally aided highways, including construction, pavement, maintenance, and policy regarding structures and bridges. For example, 23 CFR Section 626.3 requires that, âPavement shall be designed to accommodate current and predicted traffic needs in a safe, durable, and cost effective manner.â355 Section 450.206 of 23 CFR requires that states, within the scope of their statewide and nonmetropolitan planning processes, conduct comprehensive and continuing planning processes. The regulation requires that states â¦ carry out a continuing, cooperative, and comprehensive statewide transportation planning process that provides for consideration and implementation of projects, strategies, and services that will address the following factors: 1. Support the economic vitality of the United States, the States, metropolitan areas, and nonmetropolitan areas, especially by enabling global competitiveness, productivity, and efficiency; 2. Increase the safety of the transportation system for motorized and non- motorized users; 3. Increase the security of the transportation system for motorized and non- motorized users; 4. Increase accessibility and mobility of people and freight; 5. Protect and enhance the environment, promote energy conservation, improve the quality of life, and promote consistency between transportation improvements and state and local planned growth and economic development patterns; 6. Enhance the integration and connectivity of the transportation system, across and between modes throughout the state, for people and freight; 7. Promote efficient system management and operation; 8. Emphasize the preservation of the existing transportation system; 9. Improve the resiliency and reliability of the transportation system and reduce or mitigate storm water impacts of surface transportation; and 10. Enhance travel and tourism.356 These criteria are clearly broad enough that a state DOT could chose to integrate planning for C/ADSs as part of their regular planning processes. The states within our subject pool have also created statewide criteria that must be adhered to in developing long-range plans, and in developing financing plans for transportation asset management analysis. As the C/ADS fleet grows in size, states may decide that modifications to 355 23 CFR Chapter 1, Subchapter G at Part 626 at Section 626..3. Accessed at: https://www.ecfr.gov/cgi-bin/text- idx?SID=55850eced8482dae41706341ce414ce7&mc=true&node=se23.1.626_13&rgn=div8 356 Title 23, Chapter I Subchapter E Part 450 Subpart B Â§450.206. Accessed at: https://www.ecfr.gov/cgi-bin/text- idx?SID=55850eced8482dae41706341ce414ce7&mc=true&node=se23.1.450_1206&rgn=div8
NCHRP 20-102(07) Interim Report 194 current criteria may be warranted to reduce any impediments to planning, financing, and constructing new infrastructure to accommodate C/ADSs. Texas, for example, at Section 201.601 of Texas Transportation Code requires the DOT to develop a statewide transportation plan that encompasses 24 years and covers all modes of transportation, including highways, turnpikes, and mass transportation. The plan is required to contain long-term transportation goals with measureable targets for each goal.357 This is mirrored in department regulatory code at Texas Administrative Code Title 43.358 State statutes provide considerable latitude for state DOTs to include C/ADS deployment as part of their criteria for outlining transportation needs within long- and shorter-term planning documents. Michigan, for example, in its recently developed 5-year plan for 2018â2022, begins the plan with a section on C/ADSs at page four of the document, and outlines its C/ADS technology strategic plan at page five.359 Figure A3 shows a snapshot of page four of Michiganâs planning document. 357 201.601 (a)(1) and (3) and (a-1((1)) at Transportation Code, Title 6 Roadways. Accessible at: http://www.statutes.legis.state.tx.us/Docs/TN/htm/TN.201.htm#201.9911 358 Texas Administrative Code, title 43 Transportation, Chapter 16 Planning and Development of Transportation projects. Accessed at: http://texreg.sos.state.tx.us/public/readtac$ext.TacPage?sl=R&app=9&p_dir=&p_rloc=&p_tloc=&p_ploc=&pg=1& p_tac=&ti=43&pt=1&ch=16&rl=54 359 MI DOT: 2018-2022 Five year Transportation Program. Preliminary Draft July 20,2017. Accessed at: http://www.michigan.gov/documents/mdot/MDOT_5_Year_Plan_WEB_2_579719_7.pdf
NCHRP 20-102(07) Interim Report 195 Figure A3. Snapshot of Michiganâs Five-Year Transportation Plan Section on Automated and Connected Vehicles360 360 Michigan Department of Transportation, 2017