Safe Transportation Research & Education Center

Rear-end collisions would occur if vehicle speeds decrease abruptly when encountering kinematic waves (KWs) emanating from active bottlenecks. This study aims to develop a control strategy in variable speed limits (VSL) to reduce rear-end collision risks near recurrent bottlenecks. Using the crash prediction model developed for rear-end collisions related to risky KWs, the effectiveness of VSL control strategies were evaluated in the cell transmission model (CTM). Several strategies were tested in sequence to determine the best case for risk reduction. Results of this study show that the collision risk can be effectively reduced if the speed limit is lowered in an opportune occasion. The VSL needs to response quickly to the fast changing traffic condition while should simultaneously avoid the potential disturbance to the traffic. According to the simulation results, the following recommendations are made when implementing the VSL to improve safety situation near recurrent bottlenecks: moderate threshold of collision likelihood to active VSL, moderate design speed limit in VSL, fast speed change over time, and small speed difference between consecutive VSLs.

The objective of this work is to identify better metrics of exposure when comparing traffic crash risk across modes or across locations. We propose that total time travelled should be used for road user exposure to crash risk. The idea behind this is that travel time reflects the differences in speeds across different modes and hence should be used as the basic exposure metric from which crash risk based on other metrics, such as travel distance, can easily be derived. We also propose that when comparing crash risk of different modes across different locations the time-based mode share should be used as an explanatory variable. By using mode share we are generalizing the safety in numbers concept which focuses on absolute numbers. This work presents a discussion on why these two metrics were chosen and how they are different from the commonly used metrics. Quantitative evidence for the choice of time-based metrics is also presented using travel survey data to compare crash risk across modes and locations.

This paper presents a method to assess the safety of uncontrolled intersections considering both conflict probability and severity, which are two major properties of traffic conflicts. This method provides not only the safety level of the entire intersection but also the distribution of safety within intersections. Intersections are modelled by a two-dimensional Cartesian coordinate system and the internal space of intersections is divided into cells. Firstly, vehicle movement characteristics of at uncontrolled intersections are modelled. Secondly, conflict probability of each cell within the intersection is estimated considering approaching probability and lateral migration probability of vehicles. The quantification of conflict severity is based on kinetic energy loss of potential crashes. Grey cluster analysis is used to combine conflict probability and severity to model the safety assessment of each cell. Thirdly, the application of this method discussed, and an overall safety index of intersections is proposed considering weighted safety level and relative value of area with different safety levels. Finally, a case study, which includes three different designs, is presented along with visualization technique to demonstrate the results. The results not only show the validity of the model, but also indicate that the proposed method can be applied for: i) safety evaluation of existing or designed intersections; ii) dangerous position management within intersections; iii) safety assessment of designed intersections and iv) safety level comparison among different intersections or various designs for the same intersection. Using this method, engineers and planners can better evaluate and improve the safety of existing or the future uncontrolled intersections. The future work will use this approach to develop the models of other types of intersections and different road users.

This report examines two groups of individuals who are inherently not well understood to Bay Area Bike Share and other public bikesharing operators: casual users and non-users (i.e., individuals who examine the system but choose not to use it). Using publicly available data from Bay Area Bike Share’s website, researchers conducted a preliminary analysis to determine when and where intercept surveyors should be stationed. Two survey instruments were tailored specifically to casual and non-users. From the survey instruments, the researchers were able to glean information regarding demographics, socioeconomics, common trip purposes, reasons for choosing or not choosing to use Bay Area Bike Share, and other related data. Findings suggest that Bay Area Bike Share casual users are similar to annual members in educational attainment, income, and race but they differ in trip purpose, trip duration, and home city. Furthermore, researchers found that the majority of casual users did not fully understand the pricing structure, specifically relating to the fees applied to trips over 30 minutes. The pricing structure and the limited distribution of bikesharing stations were the two most frequently cited issues with the system by users and non-users. Overall, casual user satisfaction with BABS was relatively high.

Over 3,600 people died in traffic crashes in California in 2019; more than one in four people who died was a pedestrian or bicyclist (NHTSA). The burden of death and injury is unequally distributed - based on mode type, on race and ethnicity, and on income - as a consequence of historic and structurally inequitable funding and policy decisions (Archer, Sandt, Santana). Our current road network is a dichotomy of areas that connect people to things they need and underserved communities with restricted mobility. The Safe System approach offers transportation professionals with a new way of approaching safety and to improve roadways and mobility.

Originally introduced in Sweden in 1997, the Safe System approach has been gaining momentum in California and nationally with severalhigh visibility reports and publications by the National Transportation Safety Board (NTSB), Towards Zero Foundation, the Safe System Consortium, and the National Safety Council. This approach views human life and health as the paramount consideration when designing a road network (Towards Zero Foundation). The goal of a Safe System is to eliminate fatal and serious injuries for all road users by proactively putting safeguards in place and working towards sustainable mobility.

Traditionally, human behavior was considered to be the primary variable associated with traffic injury. The Safe System approach refocuses efforts to emphasize transportation system design and operation. It inherently places an emphasis on non-motorized users who are at a higher risk of death or serious injury. Most resources, including the Federal Highway Administration (FHWA), identify the key components of a Safe System as some combination of safe road users, safe vehicles, safe speeds, safe roads, and post-crash care. This Safe System further anticipates that people will make mistakes or have momentary lapses of attention, and acknowledges that the human body has a limited injury tolerance. This approach works to improve safety for all road users through multiple layers of protection, where no individual layer is 100% protective, but when several layers are combined, the overall risk is reduced.

Few resources, if any, address how to apply the Safe System framework in community engagement and planning efforts. As written, this approach relies primarily on transportation agencies to commit to a paradigm shift and adapt their work accordingly. Through our Community Pedestrian and Bicycle Safety Training Program, UC Berkeley Safe Transportation Research and Education Center (SafeTREC) and the nonprofit agency, California Walks (Cal Walks), adapted FHWA’s Safe System elements and principles to not only make it more applicable for grassroots community engagement but also to strengthen the impact of the approach. This brief will provide an overview of our thought process and set the stage for future efforts.

Public participation in government is a foundation of democracy; however, it exists on a spectrum. In the field of transportation, decision-makers may seek information by simply making public announcements to invite input. Alternatively, governments devote resources to conduct thoughtful and extensive outreach to seek meaningful input. Recently, professionals and policymakers have considered an equity approach not only to reach and engage a diverse, representative group of community members, but to develop plans, projects, and policies that are inclusive of the community. Engaging Latine1 communities requires rethinking traditional engagement and developing strategies that have considerations for the range of factors that shape this diverse community’s experience, including culture, social inequities, and socio- and geopolitical factors. This brief highlights a few best practices for engaging Latine communities.

Transportation network companies (TNCs) have played an increasingly prominent role providing on-demand mobility for consumers across California. The California Public UtilitiesCommission (CPUC) and the California Air Resources Board (CARB) have adopted and are implementing SB 1014 (Clean Miles Standard), which establishes an annual increase in the percent of zero-emission passenger miles traveled and greenhouse (GHG) emission reduction targets for TNCs. This regulation requires TNC drivers to acquire and operate an electric vehicle (EV).

With an aging state population, it is crucial to understand the factors that contribute to road safety among adults aged 65 and older and identify at-risk neighborhoods for targeted interventions. In this context, this report analyzes fatal and serious injury (FSI) trends and patterns among aging road users, including older pedestrians and bicyclists, with a focus on identifying neighborhoods at risk for crashes based on senior FSI rates. 2178 census tracts (32.7%) were deemed as being potential at-risk neighborhoods, as they all exceeded the state average senior FSI rate of 120 per 100,000 individuals (0.12%). The report also discusses factors that contribute to road safety among older adults, including physical changes associated with aging and the impact of new mobility technologies. By identifying at-risk neighborhoods and exploring factors that contribute to senior road safety, this report aims to inform targeted interventions to improve road safety for older adults.

Safe Systems is an approach to road safety that envisions the elimination of fatal and serious injuries and seeks to provide both a theoretical framework and practical roadmap for accomplishing such an ambitious goal. The Safe Systems approach involves a paradigm shift from traditional approaches to road safety planning and responsibility. This fact sheet discusses a principle integral to a Safe Systems Approach, shared responsibility for road safety.

The Community Pedestrian Bicycle Safety Training (CPBST) program trains and mobilizes communities to address pedestrian and bicycle safety and strengthens collaboration with local officials and agency staff. This research brief summarizes an evaluation of the CPBST program completed in 2018. 

UC Berkeley SafeTREC, in collaboration with California Walks, launched the Community Pedestrian and Bicycle Safety Program (CPBSP) to reduce pedestrian and bicyclist fatalities and serious injuries in California. We partner with communities across California to discuss, plan, and implement safety improvements and projects. The CPBSP prioritizes working in communities that are at disproportionate risk for road traffic injuries and addressing the safety needs of people who are underserved by traditional transportation resources and planning.

This report provides highlights from the 2023 CPBSP.

The Community Pedestrian Bicycle Safety Training (CPBST) program is a collaborative project between UC Berkeley Safe Transportation Research and Education Center (SafeTREC) and California Walks (Cal Walks) that seeks to assist communities with three goals:

Identifying and better understanding their local transportation safety needs;Developing and strengthening local partnerships between various stakeholders in their community; andGenerating a community-specific action plan for improving the safety of active transportation in their area.

These objectives are pursued through pedestrian and bicycle safety training workshops hosted by SafeTREC and Cal Walks in collaboration with community partners. Over 112 workshops have been conducted since 2009, and the program continues to provide trainings in 2022. Planning a workshop involves SafeTREC and Cal Walks working with a planning committee consisting of local stakeholders to schedule the workshop, recruit participants for the workshop, and work with the participants to develop a unique action plan with short-term, medium-term, and long-term goals for improving walking and biking safety and mobility (Leckie et al., 2021). A major feature of the workshop is an assessment of pedestrian and bicycle conditions in areas of interest in the community. 

The Community Pedestrian and Bicycle Safety Training Program (CPBST) is a joint project of the University of California Berkeley’s Safe Transportation Research and Education Center (SafeTREC) and California Walks (Cal Walks). Founded in 2009, the purpose of the CPBST is to: 

1. Educate local residents and safety advocates on how to improve pedestrian and bicycle safety;

2.Empower community partners to advocate for safety improvements in their neighborhoods; and

3. Strengthen collaborations with local officials and agency staff to make California neighborhoods safer and more pleansant for walking and bicycling.

SafeTREC and Cal Walks work with a Planning Committee, a group of local safety stakeholders, to convene a workshop, recruit participants, and tailor the curriculum to address the community’s needs and priorities. During the workshop, participants conduct a walking and biking assessment of priority areas in the community, learn about Safe System strategies to address walking and biking concerns, and develop an action plan with short-, mid-, and long-term recommendations. 

In this paper we use a case study approach to examine how airport operators are addressing bicycle access to their properties and the motivations and obstacles they face, in light of new policies to integrate bicycles, along with transit and walking, into transportation planning, design and construction, and to increase bicycles’ role in the transportation system.

Eight influential elements emerged from our review of policy documents and research literature. We used them to guide interviews with key informants. The eight elements are: governance structure, location, access roads, self-perceived environmental stewardship, spending restrictions on non-aviation transportation improvements, proximity to transit, policies and mandates to reduce environmental impacts and land use constraints. We report on seven cases, selected on the basis of inclusion in studies on key aspects of airport ground access and, for one, identification as exemplary. They are: Oakland International Airport, San Francisco International Airport, Los Angeles International Airport, Seattle-Tacoma International Airport, Boston Logan International Airport Minneapolis-St. Paul International Airport, and Portland, an exemplar recommended by several key informants. 

We limit our discussion to employee bicycle access because that has been the focus of airport operators that have made these investments and programs to reduce single-occupancy vehicle travel at airports.

In aggregating the interviews, we identified replicable approaches to improving bicycle access. We also identified examples of innovative funding for multi-modal access using revenues generated by airport Passenger Facilities Charges. Finally, we identified areas for additional research: airport employee commute needs, ground access mode choice and operator costs and benefits of bicycle access investments.

California vehicle impound law took affect on January 1, 1995. The law allows a police officer to seize a vehicle operated by a person whose license is suspended or revoked or who has never been issued a license. The seized vehicle shall then be impounded for 30 days. In California, a driver must be stopped for some other infraction before his/her license can be checked. The purpose of this evaluation is to assess the impact of Upland's vehicle impound program on traffic safety (crashes and on-the-road behavior) and police department resources and operations.

Skid resistance is one of the important serviceability indicators related to safety on wet pavements. There is a need to manage skid resistance systematically to maintain the level of safety performance of roadway surfaces. This study focused on the development of a skid resistance deterioration model based on the analysis of skid data inventory collected in California. The California Department of Transportation (Caltrans) has collected skid resistance data across the complete state highway network over the past two decades using a standard locked-wheel skid trailer, ASTM E-274. This study utilizes skid data collected on more than 300 miles of asphalt concrete freeway in California over a period of twenty years. Most of the possible factors found in previous studies to influence skid resistance were considered. Panel data parameter estimation methods were used. The results indicate that factors with the largest effects on skid resistance are the age of pavement, ADT, temperature, precipitation, and the length of the period since the last significant precipitation.

In this talk, an overview of the recently completed National Cooperative Highways Research Program project 07-19 will be presented. In NCHRP 07-19, research was conducted on a variety of methods and technologies for collecting bicyclist and pedestrian volume data. Research included a practitioner's survey, in-depth interviews with count program managers, and field testing and accuracy evaluation of six counting technologies. Counters were installed at roughly 15 different sites and evaluated for precision and reliability. The main product of this project is a guidebook on conducting counts of pedestrians and bicyclists, to be published in early 2015.

Abstract: In this talk, an overview of the recently completed National Cooperative Highways Research Program project 07-19 will be presented. In NCHRP 07-19, research was conducted on a variety of methods and technologies for collecting bicyclist and pedestrian volume data. Research included a practitioner's survey, in-depth interviews with count program managers, and field testing and accuracy evaluation of six counting technologies. Counters were installed at roughly 15 different sites and evaluated for precision and reliability. The main product of this project is a guidebook on conducting counts of pedestrians and bicyclists, to be published in early 2015.

SafeTREC webinar on Challenge Area 13 regarding Bicycle Safety data.

The leading cause of injury and death for children in California is motor vehicle crashes. To prevent these needless tragedies, the California Office of Traffic Safety (OTS), through the Business, Transportation and Housing Agency, funds child passenger safety programs throughout the state. This workbook is designed to be used by these local programs to 1) evaluate the impact of their activities on child restraint use, 2) evaluate results to improve or modify the programs as needed, and 3) meet contractual evaluation requirements. Program evaluations can be difficult for local programs due to high service demands and limited resources. We hope this guide supports local programs and agencies by providing the evaluation method and tools. A before-and-after study design is described that measures restraint use before the intervention occurs (to provide a baseline rate) and then after the intervention (to document any change). The UC Berkeley Traffic Safety Center will offer direct support and guidance to those programs using these instructions.

The 2018 California Traffic Safety Study is the ninth wave of a statewide representative survey of California vehicle drivers on traffic safety perceptions, distracted driving and level of awareness of traffic safety media outreach campaigns. The following data analyses is based on 1,395 survey responses collected in August and September of 2018.

The analyzed data only includes the valid answers for survey items, while excluding all reported “Don’t know” responses as well as response refusals. For this reason, the valid percentage of responses differs for each question due to the number of valid answers given to a particular question. The total answer per survey question is reflected in the total number of completed surveys, which are listed in each table. In addition, some questions are skipped based on selected answer and the sample sizes for each survey item vary accordingly. Due to rounding to one decimal point, some percentages presented do not always add up to the exact value of 100.0%.

All comparisons to previous years’ data refer to the comparable longitudinal field surveys conducted with California vehicle drivers since 2010. The scope and overall sample size of the 2018 survey was comparable to the sample size of the 2017 data collection.

In total, 1,395 vehicle drivers were intercepted for the study, resulting in an overall confidence interval of +/- 2.63, at a confidence level of 95%.

The public road system in the U.S. is the world’s busiest, sustaining more than 3 trillion vehiclemiles of travel each year on a network of more than 4 million miles of roads and highways. It has had enormous positive impacts on U.S. society, driving economic growth and innovation, providing mobility and opportunity to its users, and helping the U.S. maintain its global economic competitiveness. This system was built with a focus on motor vehicles; only recently has substantial funding and attention been given to transit, walking, and bicycling. There is still a huge disparity in how we travel: between 1990 and 2009 the yearly vehicle-miles traveled for passenger cars and light-duty trucks increased by 39 percent; yearly motor fuel consumption rose 27 percent, to 168 billion gallons. And for those unable or unwilling to purchase and use a private automobile for transportation, there can be disparate access to economic opportunity, services, and social interaction. Enhancing multimodal surface transportation will provide more options for travel and at the same time advance important public health goals. Doing so will expand beyond immediate goals such as investing in infrastructure, developing more sustainable transportation systems, and supporting economic recovery. Doing so will enable more distal, but equally worthy outcomes including: improving people’s health and well-being and reducing health care costs; increasing physical activity; and improving air quality and reducing consumption of fossil fuels and unwanted emissions, including those that contribute to climate change. Both the general public and the government have a strong interest in improving health, bringing down health care costs, and reducing energy use and traffic congestion. The report is divided into three chapters to focus on the following policy areas: policies that improve the environment and environmental health (Chapter 1); policies that enhance community design and promote active transportation (Chapter 2); and policies that reduce motor vehicle-related injuries and fatalities (Chapter 3).

This study examines data from the California EMS Information System (CEMSIS) to identify factors that influence prehospital time for EMS events related to motor vehicle collisions (MVCs). While only 19 percent of the United States population resides in rural areas, over half of all traffic fatalities involve rural motor vehicle collisions. Rural and urban MVCs result in similar injury severities, however relative inaccessibility of trauma centers and prehospital EMS time (activation, response, and transport time) likely contribute to the generally higher mortality rate in rural areas. For the present study, 24 CEMSIS data variables were requested, many of which involved missing data, which severely restricted the potential analysis of the impact of EMS response times. However, the findings did show that average overall EMS time (including response, scene and transport time) were approximately twice as long for collisions in rural zip codes compared with urban zip codes. Several limitations influence the interpretation of these results. Data on prehospital EMS times is missing for much of the state—even for zip codes with records of EMS events, data is likely incomplete. In addition, zip code level location data is insufficient for adequate study of the effects of the built environment and road network on prehospital time. Furthermore, according to the National EMS Information System (NEMSIS) User Manual, the national dataset suffers from selection and information bias, which are likely also present in the CEMSIS data. Although the present study cannot analyze the effect of longer prehospital times on patient outcome, other research has found that longer prehospital times may negatively impact patient health. Recommendations for reducing time from injury to appropriate medical care in rural areas include improving cell phone coverage, compliance of rural 911 center with FCC wireless, use of GPS technology, and integration of automatic vehicle location and computer aided navigation technologies into all computer-aided dispatch systems. In addition, CEMSIS should improve the coverage of their dataset and ensure that all EMS activities are recorded. To expand the type of analyses that can be conducted using CEMSIS data, EMS records must include fields that allow them to be linked to hospital and police datasets. When such data becomes available, research must be conducted to determine whether prehospital time is significantly related to patient outcome following motor vehicle collisions.

This study provides a preliminary investigation into the relationship between urbanization and traffic collisions by analyzing the spatial patterns in Sacramento County, California from 1998 to 2008 using urban land classifications and traffic collision data. The ArcGIS directional distribution tool was used to create standard deviational ellipses to investigate the distributional trend of urban land and traffic collisions over time. Statistical outputs representing changes of geographical centroids, elliptical areas, and standard distances (long and short axes) were then compared. Collisions were also subset by severity level to account for inherent differences in the spatial distribution of different types of collisions. The results provided insight into the macroscopic spatial patterns of urban land and traffic safety and their relationships. The limitations of the method and the need for further research were discussed. The approach in this study would be useful for other metropolitan areas with similarly changing development patterns and can be helpful in guiding future research comparing these two phenomena.

Growing interest in sustainable transportation systems and livable communities has created a need for more complete measures of pedestrian travel. Yet, many performance measures do not account for short pedestrian movements, such as walking between stores in a shopping district, walking from a street parking space to a building entrance, or walking from a bus stop to home. This study uses a 2009 intercept survey and the 2009 National Household Travel Survey to quantify pedestrian travel to, from, and within 20 San Francisco Bay Area shopping districts. Overall, walking was the primary travel mode for 21% of intercept survey and 10% of NHTS tours with stops in these shopping districts. However, detailed analysis of pedestrian movements showed that walking was common on respondent tours (52% of intercept survey tours included some walking) and that walking was used on the majority of trips within these shopping districts (65% of intercept survey trips and 71% of NHTS trips within the shopping districts were made by walking). In general, Urban Core and Suburban Main Street shopping districts had higher levels of pedestrian activity than Suburban Thoroughfare and Suburban Shopping Center shopping districts. The detailed analysis in this paper provides a more complete picture of pedestrian activity than is commonly shown by national and regional household survey summaries.