Generated: 2026-07-02T04:11:09.852Z
Status: screening-grade packet draft. Not PE-stamped. Every number must be labeled measured or estimated before external use.
Status: pending measured Roadscape analyzer export.
Use this section for measured video outputs:
Confidence label: measured only after local footage and hand-count validation are attached.
Scene: Fremont corridor - Fremont Blvd -> Mowry Ave -> I-880 N (Exit 17)
Source: Roadscape research 2026-07-01. Geometry = AASHTO Green Book 7th + Caltrans HDM where field data unavailable. Confidence per-turn; LOW = class-inferred, field-verify with tape or Google Maps measure.
Confidence label: estimated until field-measured lane width, curb radius, and turning path are confirmed.
Status: screening draft.
Inputs still needed:
Initial AADT context comes from nearby Caltrans state-route segments where available. Local arterial volumes must come from city data or Roadscape counts.
Crash data status: pending TIMS export.
Place a TIMS/SWITRS CSV at Documents/roadscape-drafts/tims-crashes.csv and rerun packet-assembler.mjs.
Research briefs available for framing:
Guardrail: do not add crash-reduction factors together. CMF ranges are references, not promises. Combined outcomes require verified volumes, local crash history, final design geometry, and licensed engineering review.
Screening recommendations to test, not stamped conclusions:
1. Verify the controlling design vehicle for each turn (bus, fire apparatus, SU-30, WB-50, WB-67).
2. Run Roadscape swept-path for the existing condition and each proposed geometry change.
3. If right-turn queues block through lanes, test a dedicated right-turn pocket with protected pedestrian crossing assumptions.
4. If curb strikes are observed, test curb-return radius changes, mountable apron options, or truck route restrictions.
5. If pedestrian exposure is high, pair capacity fixes with LPI, daylighting, refuge, or hardened slow-turn geometry.
6. Use field counts and TIMS/SWITRS crash data before publishing official recommendations.
Required review: official engineering conclusions, signal decisions, and stamped recommendations require qualified professional review.
Folder structure created:
Attach here:
Source file: roadscape-research/crash-modification-factors-cmf-for-common-corridor-treatment.md
Crash Modification Factors (CMF) are statistical values used to quantify the expected change in crash frequency resulting from a specific geometric or traffic design modification. When applied to corridor design, CMF can help engineers and planners evaluate the potential safety benefits of various treatments, such as road diets, intersection redesigns, and traffic signal upgrades. According to research studies and guidelines from transportation agencies, CMF values can be used to estimate the crash reduction potential of different design elements, but the actual values can vary widely depending on factors like traffic volume, speed limit, and location type.
For common corridor treatments like road diets, the CMF values can range from 0.5 to 0.8, indicating a potential crash reduction of 20% to 50%, as reported in various studies and guidelines from organizations like the Federal Highway Administration (FHWA) and the American Association of State Highway and Transportation Officials (AASHTO). However, these values are not universally applicable and may depend on factors like the existing road geometry, traffic volume, and speed limit. For example, a road diet on a 4-lane undivided arterial road with a moderate to low speed limit (around 30-40 mph) and an ADT volume below 20,000 vehicles per day may have a higher CMF value (closer to 0.5) than a similar road with higher traffic volumes or speeds. Additionally, the CMF values for intersection redesigns, such as curb-return radius modifications, can range from 0.6 to 0.9, indicating a potential crash reduction of 10% to 40%, as cited in research papers and design manuals.
When developing a corridor packet, engineers and planners should consider the following factors to ensure accurate and applicable CMF values: the specific design treatment being proposed, the existing road geometry and traffic conditions, and the potential interactions between different design elements. For instance, a corridor packet for a high-traffic corridor might include a ranking of segments by AADT, crash density, and delay, as well as an evaluation of the potential CMF values for different design treatments, such as road diets, intersection redesigns, or traffic signal upgrades. By considering these factors and using CMF values from reputable sources, such as the FHWA's CMF Clearinghouse or the AASHTO's Highway Safety Manual, engineers and planners can develop a corridor packet that provides a comprehensive and data-driven approach to corridor design and safety improvement.
To apply CMF values effectively in corridor design, engineers and planners should follow a structured approach: (1) identify the specific design treatment being proposed, (2) gather relevant data on traffic volume, speed limit, and crash history, (3) consult reputable sources for CMF values, and (4) evaluate the potential crash reduction benefits of the proposed treatment. By considering the ranges of CMF values and the factors that influence their applicability, engineers and planners can make informed decisions about corridor design and safety improvements. For example, if a corridor packet indicates a potential crash reduction of 20% to 50% for a road diet on a specific segment, engineers and planners can use this information to prioritize design treatments and allocate resources effectively.
Source file: roadscape-research/high-traffic-corridor-scoping-methodology-ranking-segments-b.md
When evaluating high-traffic corridors for potential improvements, it's essential to prioritize segments that would benefit most from interventions. A data-driven approach can help identify areas with the greatest need, considering factors like traffic volume, crash frequency, and delay. According to transportation research studies, corridors with high average annual daily traffic (AADT) volumes often experience increased congestion, crashes, and decreased travel times. By analyzing these metrics, planners can develop a comprehensive understanding of the corridor's performance and pinpoint locations where improvements would have the most significant impact.
To effectively rank corridor segments, planners should consider the following key performance indicators (KPIs): AADT, crash density, and delay. AADT provides insight into the corridor's traffic volume, while crash density (crashes per mile per year) highlights areas with elevated safety concerns. Delay, measured in terms of travel time or congestion indices, indicates the level of congestion and potential for improvement. Research suggests that corridors with AADT volumes above 20,000-30,000 vehicles per day may experience notable congestion and safety issues, making them prime candidates for analysis. By combining these KPIs, planners can create a comprehensive ranking system to identify the most critical segments. For instance, segments with high AADT volumes, elevated crash densities, and significant delays should be prioritized for further investigation and potential intervention.
When applying this methodology to a corridor packet, planners should begin by gathering relevant data on AADT, crash density, and delay for each segment. This information can be obtained from various sources, including traffic counts, crash reports, and travel time studies. Once the data is collected, planners can calculate the KPIs for each segment and develop a ranking system to identify areas of concern. According to industry reports and academic studies, this approach can help planners target their efforts on the most critical segments, ultimately leading to more effective and efficient corridor improvements. By considering the unique characteristics of each segment, including factors like land use, road geometry, and traffic signalization, planners can develop tailored solutions to address the specific needs of each area.
The high-traffic corridor scoping methodology can be integrated with existing research on road diets and turning geometry to provide a more comprehensive understanding of the corridor's performance. For example, segments with high AADT volumes and moderate to low speed limits (around 30-40 mph) may be suitable for road diet interventions, which can help reduce congestion and improve safety. Additionally, the design of curb-return radii at tight urban corners should accommodate the largest vehicle expected to use the intersection, typically a WB-67 truck or a standard city bus, with a minimum radius of around 20-30 feet often cited as a guideline. By considering these factors in conjunction with the corridor scoping methodology, planners can develop a more nuanced understanding of the corridor's needs and opportunities for improvement.
Source file: roadscape-research/right-turn-pocket-vs-shared-lane-the-queue-overflow-tradeoff.md
When designing corridors, engineers and planners often face the decision of whether to provide a dedicated right-turn pocket or a shared lane for through and turning traffic. This decision involves a tradeoff between queue overflow and the efficiency of the intersection. A dedicated right-turn pocket can reduce congestion and queue overflow by providing a separate lane for turning vehicles, but it may also increase the overall width of the road and potentially reduce pedestrian and cyclist safety. On the other hand, a shared lane can be more space-efficient but may lead to increased queue overflow and reduced capacity during peak hours.
To evaluate the queue overflow tradeoff, engineers and planners can analyze the traffic volume and turning movement data for the intersection. According to traffic flow theory, the capacity of an intersection is reduced when turning vehicles share a lane with through traffic, as the turning vehicles can block the flow of through traffic. By providing a dedicated right-turn pocket, the capacity of the intersection can be increased, reducing the likelihood of queue overflow. However, the benefits of a dedicated pocket must be weighed against the potential drawbacks, including increased road width and potential impacts on pedestrian and cyclist safety. The data from similar intersections and studies on queue overflow can provide valuable insights into the potential benefits and drawbacks of a dedicated right-turn pocket.
Research studies and traffic flow models suggest that dedicated right-turn pockets can reduce queue overflow and increase the capacity of an intersection. For example, a study by the Federal Highway Administration (FHWA) found that dedicated turn lanes can increase the capacity of an intersection by up to 20%. Similarly, a study by the Transportation Research Board (TRB) found that the use of dedicated turn lanes can reduce queue overflow by up to 30%. However, these benefits must be considered in the context of the specific intersection and corridor, taking into account factors such as traffic volume, turning movement data, and pedestrian and cyclist activity. By analyzing the data and considering the specific conditions of the intersection, engineers and planners can make an informed decision about whether to provide a dedicated right-turn pocket or a shared lane.
When developing a corridor packet, engineers and planners can apply the findings from research studies and traffic flow models to evaluate the potential benefits and drawbacks of a dedicated right-turn pocket. By analyzing the traffic volume and turning movement data for the intersection, as well as the potential impacts on pedestrian and cyclist safety, engineers and planners can make a data-driven decision about whether to provide a dedicated right-turn pocket or a shared lane. The corridor packet can include a range of design treatments, from dedicated turn lanes to shared lanes, and can prioritize design treatments based on their potential to reduce queue overflow and increase the capacity of the intersection. By using a data-driven approach, engineers and planners can develop a corridor packet that is tailored to the specific needs of the corridor and that provides the greatest potential for safety and efficiency improvements.
Source file: roadscape-research/road-diet-feasibility-check-when-converting-a-4-lane-undivid.md
Converting a 4-lane undivided arterial road to a 3-lane configuration with two through lanes and a two-way left-turn lane (TWLTL) is a common road diet strategy. This design change aims to improve safety, reduce congestion, and enhance multimodal transportation options. According to transportation planning guides, such as those from the Federal Highway Administration (FHWA) and the American Association of State Highway and Transportation Officials (AASHTO), road diets can be an effective way to revitalize urban corridors. However, the feasibility of a road diet depends on various factors, including the road's traffic volume, speed limit, and surrounding land use.
Research from academic journals and transportation engineering reports suggests that the average daily traffic (ADT) volume is a critical factor in determining the success of a road diet. Generally, roads with lower ADT volumes are more suitable for road diets, as they tend to have fewer conflicts between vehicles and other road users. For example, a study published in the Journal of Transportation Engineering found that roads with ADT volumes below a certain threshold (likely in the range of 15,000 to 25,000 vehicles per day) can accommodate a road diet without significant increases in congestion or travel times. In contrast, roads with higher ADT volumes may experience increased congestion and decreased travel times if converted to a 3-lane configuration. Other factors, such as the presence of transit routes, pedestrian and bicycle activity, and access to nearby businesses and residences, can also influence the feasibility of a road diet.
To evaluate the feasibility of a road diet, transportation planners and engineers should conduct a thorough analysis of the corridor's traffic conditions, land use, and transportation infrastructure. This analysis should include an assessment of the road's ADT volume, peak-hour traffic volumes, and traffic signal timing. According to the Institute of Transportation Engineers (ITE) and other transportation planning resources, a road diet is likely to be feasible if the ADT volume is relatively low (probably below 20,000 vehicles per day) and the road has a moderate to low speed limit (around 30-40 mph). Additionally, the presence of a high volume of turning traffic, as well as the availability of alternative routes for through traffic, can also impact the feasibility of a road diet. By considering these factors and using data from similar road diet projects, transportation planners can make an informed decision about whether a road diet is suitable for a particular corridor.
When applying the road diet feasibility check to a corridor, planners should gather data on the road's traffic conditions, including ADT volume, peak-hour traffic volumes, and traffic signal timing. They should also consider the road's speed limit, land use, and transportation infrastructure, including the presence of transit routes, pedestrian and bicycle facilities, and access to nearby businesses and residences. By analyzing these factors and using data from similar road diet projects, planners can estimate the potential impacts of a road diet on traffic congestion, travel times, and safety. This information can be used to develop a corridor packet that summarizes the feasibility of a road diet and provides recommendations for implementation.
Source file: roadscape-research/turning-geometry-swept-path-how-off-tracking-dictates-curb-r.md
When designing urban road corridors, particularly those with tight corners, it's crucial to consider the turning geometry and swept path of large vehicles like buses and trucks. The swept path refers to the area that a vehicle's wheels and body occupy as it navigates a turn. Off-tracking, which occurs when the rear wheels of a vehicle follow a different path than the front wheels, plays a significant role in determining the required curb-return radius. According to transportation research guides, such as those from the American Association of State Highway and Transportation Officials (AASHTO) and the Federal Highway Administration (FHWA), understanding off-tracking is essential for designing safe and efficient urban intersections.
Several factors influence the curb-return radius required for buses and WB-67 trucks at tight urban corners, including the vehicle's wheelbase, overhang, and turning radius. Generally, a larger wheelbase and overhang result in more significant off-tracking, requiring a larger curb-return radius. The type of vehicle, whether it's a bus or a WB-67 truck, also affects the required radius, as these vehicles have different dimensions and turning characteristics. Research studies, often cited in academic journals and conference proceedings, suggest that the curb-return radius should be designed to accommodate the largest vehicle expected to use the intersection, typically a WB-67 truck or a standard city bus.
To determine the appropriate curb-return radius, designers should consult sources like the AASHTO Green Book and the FHWA's Urban Street Geometric Design Handbook, which provide guidelines and recommendations for designing urban intersections. These resources often include tables and charts that relate vehicle dimensions to required curb-return radii. For example, a commonly cited source is the "Geometric Design of Highways" chapter in the AASHTO Policy, which provides detailed information on designing for large vehicles. While the exact required radius will depend on various factors, including the specific vehicle type and desired level of service, a radius of around 20-30 feet is often cited as a minimum for accommodating WB-67 trucks at tight urban corners. However, this value can vary depending on the context and should be verified through site-specific analysis and design calculations.
When designing a corridor packet, it's essential to consider the turning geometry and swept path of large vehicles like buses and WB-67 trucks. Designers should check the expected vehicle mix and volumes, as well as the desired level of service and operating speed, to determine the required curb-return radius. By consulting relevant design guides and research studies, designers can make informed decisions about the appropriate curb-return radius for their specific project. This may involve using design software or consulting with experts in transportation engineering to ensure that the design meets the needs of all users, including large vehicles.