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Dedicating Lanes for Priority or Exclusive Use by Connected and Automated Vehicles (2018)

Chapter: Chapter 8 - Guidance on Operational Characteristics and Impacts

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Suggested Citation:"Chapter 8 - Guidance on Operational Characteristics and Impacts." National Academies of Sciences, Engineering, and Medicine. 2018. Dedicating Lanes for Priority or Exclusive Use by Connected and Automated Vehicles. Washington, DC: The National Academies Press. doi: 10.17226/25366.
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Suggested Citation:"Chapter 8 - Guidance on Operational Characteristics and Impacts." National Academies of Sciences, Engineering, and Medicine. 2018. Dedicating Lanes for Priority or Exclusive Use by Connected and Automated Vehicles. Washington, DC: The National Academies Press. doi: 10.17226/25366.
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Suggested Citation:"Chapter 8 - Guidance on Operational Characteristics and Impacts." National Academies of Sciences, Engineering, and Medicine. 2018. Dedicating Lanes for Priority or Exclusive Use by Connected and Automated Vehicles. Washington, DC: The National Academies Press. doi: 10.17226/25366.
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Suggested Citation:"Chapter 8 - Guidance on Operational Characteristics and Impacts." National Academies of Sciences, Engineering, and Medicine. 2018. Dedicating Lanes for Priority or Exclusive Use by Connected and Automated Vehicles. Washington, DC: The National Academies Press. doi: 10.17226/25366.
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Suggested Citation:"Chapter 8 - Guidance on Operational Characteristics and Impacts." National Academies of Sciences, Engineering, and Medicine. 2018. Dedicating Lanes for Priority or Exclusive Use by Connected and Automated Vehicles. Washington, DC: The National Academies Press. doi: 10.17226/25366.
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Suggested Citation:"Chapter 8 - Guidance on Operational Characteristics and Impacts." National Academies of Sciences, Engineering, and Medicine. 2018. Dedicating Lanes for Priority or Exclusive Use by Connected and Automated Vehicles. Washington, DC: The National Academies Press. doi: 10.17226/25366.
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Suggested Citation:"Chapter 8 - Guidance on Operational Characteristics and Impacts." National Academies of Sciences, Engineering, and Medicine. 2018. Dedicating Lanes for Priority or Exclusive Use by Connected and Automated Vehicles. Washington, DC: The National Academies Press. doi: 10.17226/25366.
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Suggested Citation:"Chapter 8 - Guidance on Operational Characteristics and Impacts." National Academies of Sciences, Engineering, and Medicine. 2018. Dedicating Lanes for Priority or Exclusive Use by Connected and Automated Vehicles. Washington, DC: The National Academies Press. doi: 10.17226/25366.
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Suggested Citation:"Chapter 8 - Guidance on Operational Characteristics and Impacts." National Academies of Sciences, Engineering, and Medicine. 2018. Dedicating Lanes for Priority or Exclusive Use by Connected and Automated Vehicles. Washington, DC: The National Academies Press. doi: 10.17226/25366.
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Suggested Citation:"Chapter 8 - Guidance on Operational Characteristics and Impacts." National Academies of Sciences, Engineering, and Medicine. 2018. Dedicating Lanes for Priority or Exclusive Use by Connected and Automated Vehicles. Washington, DC: The National Academies Press. doi: 10.17226/25366.
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Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

122 Based on the analysis described in the previous chapters, the project team developed guidance for agencies regarding dedicating lanes to CAVs. The guidance provided in this chapter related to the operational characteristics and impacts of dedicating lanes to CAVs are representative of the scenarios that were explicitly modeled in this project, and may not be representative of a wider range of scenarios. 8.1 Shared and Exclusive DLs For purposes of this guidance, the following definitions also will be helpful: Priority DLs: Lanes on which CAVs share the access privileges with HOVs. Exclusive Lane Access: Only CAVs are allowed on the DLs. Based on the simulation scenarios, the study team found that the CAV application provides overall system benefits when the CAVs: • Share lanes with HOVs (at lower rates of market penetration) or • Have exclusive lane access (at a market penetration level that was at least proportional to the number of lanes dedicated to their exclusive use so that all lanes are fully utilized). 8.1.1 CACC-Equipped Vehicles The research team’s findings suggest that, at lower MPRs (up to 10%), allowing both CACC-equipped vehicles and HOVs on the DLs improves lane utilization. Specifically, when the corridor already has an HOV DL, it makes sense to allow CACC-equipped vehicles. The CACC-equipped vehicles increase the lane capacity and lane utilization beyond what is possible in an HOV-only DL. This analysis did not consider person-throughput but only vehicle throughput, because the models used were not calibrated to a level of observed vehicle occupancy. As the MPR increases, the benefits of dedicating lanes to CACC-equipped vehicles for exclu- sive use become clearer. At MPRs approaching 25% and increasing between 25% and 45%, the research suggests that dedicating lanes to CACC-equipped vehicles for exclusive use can improve system efficiency in two ways: • By granting exclusive access for CACC-equipped vehicles to the DLs, these lanes see 100% market penetration, which improves the lane capacity to up to 3,500 vphpl. • By improving the capacity of DLs and encouraging CACC-equipped vehicles to use DLs, the demand on the GPLs drops significantly, thereby improving overall system efficiency. C H A P T E R 8 Guidance on Operational Characteristics and Impacts

Guidance on Operational Characteristics and Impacts 123 As the market penetration of CACC-equipped vehicles increases beyond 45%, mobility ben- efits will likely occur even without dedicating lanes to CAVs. Significantly, the project team did not model scenarios in which more than one DL was provided for exclusive use by CAVs. Other studies have shown that at higher market penetrations it becomes beneficial to dedicate addi- tional lanes to exclusive CAV usage, maintaining a balance so that the DLs and GPLs remain well utilized (Liu et al. 2018). Figure 8.1 represents guidance on when to share and when not to share dedicated CAV lanes with HOVs, in terms of market penetration of CACC-equipped vehicles. 8.1.2 DSH-Equipped Vehicles Performing a similar analysis for DSH-equipped vehicles, the research team found that the DSH application does not increase lane capacity. The analysis suggests that the presence of DSH-equipped vehicles reduces lane throughput but improves overall safety by reducing the speed differential and shockwaves. By harmonizing speeds, the DSH application could poten- tially reduce the “snail” effect. 8.2 Expected Benefits and Disbenefits from Dedicating Lanes to CAV Users As discussed in Chapter 2 of this report, this research also considered factors affecting the expected benefits and disbenefits to various stakeholders from dedicating lanes to CAV users on a priority basis, shared basis, or exclusive basis. This section describes the assessment of the performance measures and sensitivity parameters discussed in Chapter 2, based on the modeling and simulation analysis performed. 8.2.1 Market Penetration For purposes of this report, market penetration has been defined as the percentage of the overall vehicle population that is equipped with CAV technology and applications. The impact of market penetration was assessed both with and without DLs for CAV applications. The analy- sis suggests that mobility benefits increase with increasing market penetration with the CACC application, and that safety benefits increase with increasing market penetration with the DSH application. The rest of this section presents specific guidance for expected benefits to differing stakeholders. 8.2.1.1 CACC-Equipped Vehicles The research team assessed the impact of CACC applications with MPRs up to 45% and found that the DL throughput increased to up to 3,400 vehicles per lane per hour. For market penetrations greater than 45%, although no lane was dedicated to CAV users in the analy- sis, there were overall benefits. Similarly, the benefits due to DSH application included reduc- tion in speed differentials and shockwaves, which in turn improved roadway safety. Table 8.1 Figure 8.1. Mapping of ideal DL characteristics based on market penetration (single DLs only). Market Penetration of CACC-Equipped Vehicles

124 Dedicating Lanes for Priority or Exclusive Use by Connected and Automated Vehicles illustrates the benefits and disbenefits to users of DLs and GPLs when CACC-equipped vehicles have shared or exclusive access to DLs. The actual increase in person-throughput would differ from the vehicle throughput, because CACC-equipped vehicles might be SOVs, whereas the baseline DL usage was exclusive to HOVs. Additionally, the analysis of differing levels of market penetration assumed the same percentage of HOVs as the base case, given the lack of indicators regarding change in vehicle occupancy due to changes in DL policies. Benefits to Users of DLs and GPLs. The mobility benefits to users of DLs manifest as an increase in travel speed. As market penetration increases, the throughput increases. In the sce- narios examined, throughput increased from an average of 2,100 vphpl in the baseline case to 3,400 vphpl at 45% market penetration, representing a system operator or societal benefit rather than an individual user benefit. The travel speeds on the DLs also remain high, but reduce gradu- ally as market penetration increases and more equipped vehicles “choose” the DLs. Based on the research, however, the travel speeds on the DLs can be expected to remain higher than the travel speeds on the GPLs even at higher MPRs. As far as emissions and fuel consumption are con- cerned, the study suggests that the users of the facility can save an average of 16% fuel at 25% market penetration. At higher market penetrations (e.g., 35% and 45%), these savings increase to almost 40%, primarily due to reductions in delays and stops. Although there are benefits to users of DLs at all levels of market penetration, the impacts on GPL users differ based on market penetration. At a lower market penetration (10%), the analysis suggests that significant disbenefits accrue to GPL users when CACC-equipped vehicles receive exclusive access to DLs because the DL is underutilized while the GPLs are overburdened. When the DLs are shared with HOVs, however, there is a slight benefit to GPL users in terms of mobil- ity. At higher MPRs (e.g., greater than 25%), significant benefits accrue to GPL users in addition to the benefits to DL users. As shown in Table 8.1, at lower levels of market penetration, sharing DLs or providing exclu- sive DL access provides slight and significant mobility benefits to DL users. Under exclusive lane use, however, GPL users see a significant reduction in their travel speeds. This pattern suggests that it is ideal to share DLs with HOVs at lower levels of market penetration. At higher MPRs (e.g., 25% to 45%), exclusive DLs for CACC-equipped vehicles improves the mobility Lane Use Type (CACC-Equipped Vehicles) Stakeholder Group Lower Market Penetraon (10%) Higher Market Penetraon (25% to 45%) Travel Speed Energy/ Emissions Travel Speed Energy/ Emissions Shared Dedicated Lanes DL Users Slight Increase No Change N/A N/A GPL Users Slight Increase No Change N/A N/A Exclusive Dedicated Lanes DL Users Significant Increase Slight Reducon Moderate to Significant Increase Moderate to Significant Reducon GPL Users Significant Reducon Significant Increase Slight to Moderate Increase Slight to Moderate Reducon Table 8.1. Benefits and disbenefits of dedicating lanes to CACC-equipped vehicles to both DL and GPL users.

Guidance on Operational Characteristics and Impacts 125 and environmental performance of both sets of users. At still higher market penetration levels, dedicating additional lanes for use by the CACC-equipped vehicles provides additional benefits when the number of dedicated lanes is well matched to the market penetration so that all lanes are well utilized. Benefits to Owners and Operators of the Facilities. Owners and operators of the facilities also achieve benefits when CACC-equipped vehicles are allowed or provided exclusive access to DLs. For example, the modeled scenarios provided evidence of improved throughput of the system in a DL setting as well as reduced energy use and emissions. In addition, the following lane dedication scenarios provided benefits for DL users and GPL users from an equity standpoint: • At lower market penetration levels, shared DLs between HOV vehicles and CACC-equipped vehicles increased travel speeds on both the DLs and GPLs. • At higher market penetration levels, exclusive DLs for CACC-equipped vehicles increased travel speeds on the DLs, because all vehicles in the DL were CAVs; exclusive DLs for CACC- equipped vehicles also increased travel speeds on the GPLs, because the demand on the GPLs was reduced. 8.2.1.2 DSH-Equipped Vehicles Similarly, Table 8.2 demonstrates the benefits and disbenefits to users of DLs and GPLs when DSH-equipped vehicles have shared or exclusive access to DLs. Unlike the CACC scenarios, DLs did not cause a significant increase in throughput for the DSH application; therefore, they were used only up to 25% CAV market penetration. (For higher MPRs the research team assessed scenarios without DLs.) As shown in the table, shared DLs caused a slight reduction in speed differential and shock- waves when the DSH market penetration was lower (10%). This reduction was seen among both DL users and GPL users. In the case of exclusive DLs, it appeared that only the DL users received the benefits. At lower levels of market penetration, the GPL users experience significant disbenefits. At higher levels of market penetration, however, GPL users experience no significant benefit or disbenefit. No statistically significant change was found in the energy consumption or emissions. Lane Use Type (DSH-Equipped Vehicles) Stakeholder Group Lower Market Penetraon (10%) Higher Market Penetraon (25%) Speed Diff./ Shockwaves Energy/ Emissions Speed Diff./ Shockwaves Energy/ Emissions Shared Dedicated Lanes DL Users Slight Reduc on No Change N/A N/A GPL Users Slight Reduc on No Change N/A N/A Exclusive Dedicated Lanes DL Users Slight Reduc on Slight Reduc on Moderate to Significant Reduc on Slight Reduc on GPL Users Significant Reduc on Significant Increase No Change No Change Table 8.2. Benefits and disbenefits of dedicating lanes to DSH-equipped vehicles to both DL and GPL users.

126 Dedicating Lanes for Priority or Exclusive Use by Connected and Automated Vehicles As far as system-wide benefits are concerned, there is some benefit when DSH-equipped vehicles share the DLs with HOVs at lower market penetration, and when DSH-equipped vehicles have exclusive lane access in the case of higher market penetrations. For market penetra- tions higher than 25%, safety-related benefits are demonstrated when no DLs are used. 8.2.2 Impact of Combination of Applications Two CAV applications—CACC and DSH—were assessed in this project. The CACC applica- tion aims to improve the mobility of freeway lanes by coordinating the maneuvers of vehicles and driving them closer together so that they act as a string with virtual connectivity. The DSH application aims to harmonize the speeds across the freeway, thereby reducing sudden speed- changes to reduce shockwaves and increase safety. When implemented together, the modeling included CACC strings as a platoon of vehicles in which the lead vehicle received “harmonized” speed recommendations in response to downstream congestion. The combination of applica- tions produced both safety and mobility benefits when compared to the baseline. 8.2.3 Impact of Demand The impact of dedicating lanes to CACC-equipped vehicles and DSH-equipped vehicles was assessed using varying demand conditions for the I-66 and US-101 corridors. Table 8.3 shows how the percentage change in average system throughput due to CAV DLs is impacted by changes in demand levels. A “lower than peak” scenario was not simulated for the US-101 testbed, and the two cases represent a 0.2-fold increase or decrease in typical peak demand. As shown in the table, the performance of the CACC application in terms of percentage change in throughput improved with increased demand beyond typical demand. With reduced demand, however, the performance remained unchanged. The DSH application, which typi- cally reduced the throughput when implemented, slightly increased the throughput under higher demands. Scenario Corridor Used for Analysis Change in Average Vehicle Throughput Lower than Peak Demand Peak Demand Higher than Peak Demand 10% Market Penetration of CACC (Shared DL) I-66 Northern Virginia Slight Increase Slight Increase Moderate Increase US-101 San Mateo, California N/A No Change Moderate Increase 25% Market Penetration of CACC (Exclusive DL) US-101 San Mateo, California N/A Moderate Increase Slight Increase 50% Market Penetration of CACC (No DL) US-101 San Mateo, California N/A Moderate Increase Moderate Increase 10% Market Penetration of DSH (Shared DL) I-66 Northern Virginia No Change Moderate Reduction No Change Table 8.3. Impact of demand on benefits from CACC and DSH DLs.

Guidance on Operational Characteristics and Impacts 127 When CACC was assessed for the US-101 corridor, increasing traffic beyond typical peak traffic did not cause further increase in throughput. This result was primarily due to the fact that the US-101 traffic density was already approaching saturation at typical peak traffic conditions. 8.3 Guidance on Access Restrictions As described in Chapter 2, access points or restrictions influence the design of DLs for CAVs. Restricting access to DLs serves two purposes: (1) it delineates CAVs from other users, increasing safety in situations of high lane friction, and (2) it reduces the overall disturbances in the flow of traffic on the DLs by concentrating these disturbances to a reduced number of access points. Restricting access to DLs also can have some apparent disadvantages: (1) DL users need to man- age their exit points from the GPLs, allowing ample time for the vehicles to cross over the GPLs to the designated entries to the DLs, and (2) CAV users who need to use the DL for short dis- tances are discouraged from using it because of the limited availability of entry and exit points. Based on this project’s comparison of system performance during continuous and restricted access scenarios (as described in Chapter 6), the following guidance statements can be made: • Mobility benefits increase when there is continuous access to the DLs. This result occurs because even vehicles taking shorter trips can utilize the DLs. • Speed differentials between DLs and GPLs increase with restricted access to DLs. DLs with exclusive access for CAVs will have a much higher travel speed than GPLs. Average travel speeds on GPLs reduce significantly when there is restricted access to DLs. This result occurs because the demand on GPLs will be higher when compared to continuous access, as vehicles taking shorter trips cannot use the DLs. The analysis conducted for this study did not include scenarios with higher levels of market penetration (i.e., 35% to 45%) by users utilizing DL with restricted access. Additional research is warranted to further this analysis. Moreover, other studies have found significant differ- ences in the way drivers behave in weaving sections (in the case of restricted access dedicated lanes), and this behavior needs to be further studied to conclude whether these findings can be generalized. 8.4 Guidance on Lane Separation Barriers This analysis used lane friction as the performance measure to develop guidance regarding lane separation barriers. Lane friction is defined as the difference in travel speeds between vehi- cles on the DLs and vehicles in the GPLs. More lane friction (a higher speed differential) between DLs and GPLs can render lane changes into and out of DLs unsafe, and therefore warrants the use of restricted lane access or physical barriers/lateral spacing between DLs and GPLs. Based on the observed average lane friction, the research team categorized the scenarios into four groups (see Figure 8.2): • High Market Penetration of CAV with shared DLs with HOVs. This group demonstrated the lowest lane friction, and does not warrant lane separation barriers or restricted lane access. • Low Market Penetration of CAV with shared DLs with HOVs. This group also demonstrated relatively low lane friction. • High Market Penetration of CAV with Exclusive DLs. This group showed medium lane fric- tion, where the average speeds of the DL and the adjacent GPL differed by 10 mph to 15 mph. According to Best Practices: Separation Devices Between Toll Lanes and Free Lanes (Hlavacek et al. 2007), this level of lane friction does not warrant physical separators, but rather buffer- separated double solid lines.

128 Dedicating Lanes for Priority or Exclusive Use by Connected and Automated Vehicles • Low Market Penetration of CAV with Exclusive DLs. This group showed the highest lane frictions, on the order of 30 mph. This result warrants the need for physical separators for both enforcement and safety purposes. This guidance is based on the modeling-based analysis that was performed in this project. For more detailed design considerations, additional field data collection and alternative analy- sis are proposed. 8.5 Findings on Economic Equity The project team also conducted a simplified VTTS analysis to compare the benefits that DL users will see. This evaluation used the national average VTTS values, averaged between busi- ness purpose and personal trip purpose. Annual savings were computed based on these average values and other assumptions highlighted in Chapter 6. In general, the DL users saved more travel time than the GPL users. GPL users saw fewer (and sometimes no) travel time benefits when compared to the DL users. The intensity of this mismatch appeared to depend on market penetration. The DL users received maximum benefits under 10% market penetration when CAVs had exclusive lane access to the DLs. Under 25% market penetration, however, DL users with exclusive lane access also demonstrated some annual economic savings. For market pen- etrations higher than 25%, there was no significant difference in travel time savings between DL and GPL users. Please note that there may be other scenarios outside of our analysis space that could potentially provide greater travel time savings for both DL and GPL users. 8.6 Regulatory and Policy Guidance Consideration of definitions for dedicating lanes requires an agreed-upon framework of deci- sions. Will the lanes be restricted to vehicles based on their class, type, amount of automation, or connectivity? Will the levels of technology installed in the roadway or roadside influence such restrictions? Having clear definitions of differing types of functionality will be crucial for enforcement in allowing vehicles to operate in DLs of any type, and crucial in determining the potential HOV/HOT exemption eligibility of specific vehicles. The challenge that exists today is the overlap in functionality and difficulty in differentiating between a vehicle capable of automatically handling a dynamic driving task and a vehicle that is actually operating in such a mode. Human drivers will be able to select the mode of usage of a vehicle that is equipped with an ADS, and that could include differing levels of automation at different times and under different operating conditions. States will need to decide whether it is important to impose restrictions on which types of automation should be used, at which times, and in which DL locations. It also will be important to harmonize these state decisions with the federal rules that govern the requirements on HOV and HOT lanes when the CAV DLs are coincident with HOV or HOT lanes. Lane Friction Between DL and Adjacent GPL Figure 8.2. Mapping of lane friction as a characteristic of DLs and CAV market penetration.

Guidance on Operational Characteristics and Impacts 129 As they begin to contemplate dedicating lanes for CAVs, state and local DOTs, metropolitan planning organizations, and infrastructure owners and operators are trying to determine what CV infrastructure needs to be deployed, where to deploy it, and when to deploy it. Further- more, these agencies are struggling with the issue of how to fund and/or finance this deploy- ment. They also are trying to prepare for the future of AVs and asking the question: what roadway infrastructure (e.g., pavement markings, signing, etc.) will be needed to optimize the performance of the AV safety systems? These infrastructure owners and operators want to know what infrastructure can be provided to enhance the performance and safety of vehicles with low-level automation (i.e., automated braking and lane departure systems) as well as highly automated vehicles. Discussion about how to answer the “road readiness” question is increasingly common within agencies, as is the recognition that the future will reflect a balance between proactive implemen- tation and reactive adjustments. Because differing vehicle developers will use differing combi- nations of sensors, with differing levels of sophistication, it is not feasible at present to specify a single level of infrastructure specifications that can ensure suitability for use by ADS. Therefore, initial decisions on the types of vehicles that can be given DLs will most likely be based on vehicle types and levels of automation, because those definitions are the most mature. As this issue evolves, the research team suggests revisiting the guidance provided by this study and determin- ing whether roadway definitions will have a significant or minimal impact on the allowance of DLs for CAVs. Some designation of roadways with respect to the quality of lane markings and signage could be important for future efforts to license CAVs for broader public use. With SAE International Level 4 and Level 5 systems, considering whether detailed digital maps are available for roadways will likely be important. It also will be important to identify roadway geometric limitations and turning radius restrictions on maps for trucks. Therefore, some consideration of roadway characteristics will likely come into play. To avoid compounding the patchwork of vehicle definitions that has resulted from cur- rent policy for low-emission and energy-efficient vehicle exemptions to HOV facilities across different states, it would be wise to begin addressing CAV DLs by focusing on the creation of a standard set of vehicle definitions as prescribed by the industry. This focus is currently reflected in SAE International’s SAE J3016: Recommended Practice (SAE International 2018). Presumably, SAE J3016 will be adapted to follow any changes should industry evolve its thinking. Currently, the classification scheme in SAE J3016 only represents the division of functions between the driver and the driving automation system; it does not attempt precise classifications of the Operational Design Domain (ODD) elements, which will be much more complicated. Future standardization efforts may define some representative ODD clusters as well, but this task will be challenging because there are so many dimensions to the ODD and these will depend on the capabilities of different sensing technologies and information- processing approaches that various vehicle developers will choose to adopt. Standards to define the roadway infrastructure characteristics also are likely to be rather general, along the lines of Interstate Highway design standards, rather than highly prescriptive, because the local geo- graphical constraints will vary widely across the country. The developer of each driving automation system will have to determine on which specific roads their system is capable of driving safely, and those are the roads that will be included within its ODD. Already, Level 2 automation systems such as the GM Super Cruise system are configured so that they can be engaged only on the freeways that GM has approved for its use. Given the current state of the industry, Levels 3, 4, and 5, defined in SAE J3016 and adopted in the 2017 NHTSA policy as Automated Driving Systems, would be logical initial break-points for dedicating lanes based on vehicle levels of automation.

130 Dedicating Lanes for Priority or Exclusive Use by Connected and Automated Vehicles For the foreseeable future, the large majority of CAVs that could potentially benefit from dedicated lanes will be at the lower levels of automation, with SAE Level 1 and Level 2 driving automation systems, so there is no reason to discriminate among levels of automation in deter- mining which vehicles should have access to the DLs. Rather, the important criterion for DL access should be the use of connectivity, because the concentration of connected vehicles in the DL is the fundamental way of gaining benefits. For example, vehicles without any automation but with V2V communication capability can serve as the Leaders for CACC-equipped Follower vehicles, helping to accelerate the benefits from CACC during the period when the market pen- etration of CACC-equipped vehicles remains low. Level 4 vehicles without connectivity have the potential to actually degrade highway throughput and traffic flow stability, whereas Level 1 vehicles using CACC could significantly improve these performance measures. Admitting connected vehicles to the dedicated lanes by use of their communication devices (and assessing any needed user fees) will be straightforward, as the process is directly analogous to the use of electronic tolling tags as the means of admission to HOT lanes today. Additional considerations would come into play if levels of driving automation functionality and connectiv- ity were to become the basis for implementation of dedicating lanes. For example, the methods of identification would also need to be standardized across states to reduce complexity for law enforcement and avoid the patchwork of definitions currently seen with AFV use in HOV/HOT lanes. Some complexities also would be associated with determining the conditions in which the ADS should be engaged. An ADS may be engaged or disengaged by a human driver at any time, and in some cases the local conditions are likely to deviate from the minimum ODD con- ditions for use of some specific ADS; consequently, those ADS will not be capable of operating continuously. Additional reasons why identification of ADS as the pre-screening criterion for dedicating lanes would be problematic include: • Because Level 3, Level 4, and even Level 5 vehicles can still have the human driver engaged in certain situations, it can be unclear whether a human driver or ADS is operating the vehicle in a lane that is theoretically dedicated to AV operations; and • Given that vehicle identification in relation to vehicle automation has not yet been addressed in a significant way, enforcement officials and systems cannot easily identify whether a vehicle is actually being operated under human or automatic control (other than via the vehicle communication system indicating its real-time status). In the face of these uncertainties, developing policies for operations, management, and enforcement presents several technical and institutional challenges that have not yet been addressed. Much like the uncertainty surrounding HOV/HOT enforcement (i.e., identifying vehicle occupancy), attempting to monitor and enforce vehicle automation is not an immediate consideration by the vehicle industry at this stage of CAV evolution. 8.7 Guidance Regarding Updating Laws and Regulations Attempting to establish any kind of regulatory or legislative foundation while operating in a state of constant change and high uncertainty brings with it many challenges. As a result, any policy, regulatory, or legislative actions that are taken should be incremental in nature, incor- porating graduated approaches to change and flexibility through moderation. It is suggested that agencies not attempt to solve every eventuality in one action; rather, it will be productive to consider pilot programs and small increments of change as agencies navigate through this fast-evolving environment.

Guidance on Operational Characteristics and Impacts 131 Public opinions are still being formed and are at a volatile stage as the boundaries between imagination and reality become more clearly defined in the public mind. The initial “hype” period will likely yield to a more realistic assessment of opportunities and risks, especially in light of the early 2018 crash of an automated Uber vehicle (Bliss 2018). Surveys of public opinion have already displayed wide divergence on the desirability and safety of automation of road vehicles. Dedicating lanes to AVs brings in the added dimension of distributional equity and may risk being perceived as introducing elite “Lexus Lanes,” so it is important to tread carefully and build public consensus about the broader societal desirability of dedicating CAV lanes before implementing actions. Various operational and policy issues remain unaddressed, truck platooning issues loom large, and questions about exemptions for CAVs in HOV/HOT lanes are still unclear. For all vehicles, a rich understanding of state laws that might restrict or inhibit the testing or use of ADS comes with the territory. For trucks, a keen understanding of current laws related to following distances is important. As federal laws and regulations mature, it will be important to revisit this topic regularly. Currently, the stage is being set for future precedent; now, more than ever, it is important to respect flexibility.

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TRB’s National Cooperative Highway Research Program (NCHRP) Research Report 891: Dedicating Lanes for Priority or Exclusive Use by Connected and Automated Vehicles identifies and evaluates opportunities, constraints, and guiding principles for implementing dedicated lanes for connected and automated vehicles. This report describes conditions amenable to dedicating lanes for users of these vehicles and develops the necessary guidance to deploy them in a safe and efficient manner. This analysis helps identify potential impacts associated with various conditions affecting lane dedication, market penetration, evolving technology, and changing demand.

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