Transport Research International Documentation (TRID)

Bioretention Flow-Through Planter Performance and Design Considerations

Tue, 27 Jan 2026 16:16:12 GMT

This study monitored four bioretention planters installed at Stevens Institute of Technology providing information on the hydrologic mitigation potential of planters and design considerations for future guidance. Monitoring during 18 months spanning 3 calendar years compared performance against several bioretention system design objectives, including fully captured events, peak flow reduction, and runoff retention. Hydraulic loading ratio and media porosity affected the fraction of captured events, with one-fifth of the events completely captured. The captured storms were less than 2.0 mm/m2 of drainage area 77% of the time. The planters halved the peak flow rate for 61% of observations. The entire media volume was wetted in almost half of the events but rarely fully saturated. A modified available water capacity calculation based on the difference between the field capacity and the lowest measured volumetric water content provided a useful estimate of the median retention per event. To use this estimator, it is proposed to estimate the modified available water capacity as the difference between the laboratory-measured field capacity and a laboratory-measured wilting point increased by a factor of safety to account for the practical issue that the planters never dried fully between rain events in the New Jersey temperate climate.

Addressing Local Parameter Sensitivity for Climate Resilient Urban Stormwater Modeling and Decision Making

Tue, 27 Jan 2026 16:16:12 GMT

Urban stormwater modeling is essential for informing climate resilient stormwater infrastructure. Modeling decisions can introduce hidden or unknown biases, uncertainties, and/or tradeoffs, as calibrated urban stormwater models exhibit low transferability. This means that a model’s good performance in one location or under one set of conditions/events does not guarantee good performance in other locations or under other conditions/events. We demonstrated the low transferability of a one-dimensional dual drainage stormwater model by exploring the effect of calibration decisions on model performance for a community in Pittsburgh, Pennsylvania, USA. We found the monitoring location and size of storms used for calibration can affect accurate representation of block-scale urban stormwater flows. Calibrating the model at one location did not improve model performance at other locations. We thus applied a decision analysis framework to identify the model parameters that performed best across locations and storms. The preferred model parameters for a risk-averse decision maker led to increased flooding under future design storms, but also led to differences between observed real-world inputs and final calibrated parameters for key variables. Depending on the design storm, the change in modeled flooded infrastructure associated with parameter sensitivity was comparable to the change in modeled flooded infrastructure associated with climate change. Design storms under climate change were scaled with a linear multiplicative change factor, which led to nonlinear increases in modeled flooded infrastructure. Our work highlights several critical decisions that must be made throughout the modeling process to responsibly inform the design, adaptation, and planning of climate resilient stormwater infrastructure.

Phosphorus Removal Capacity, Arsenic Leaching, and PFAS Content of Drinking Water Treatment Residuals with Potential to Enhance Stormwater Infrastructure in New England

Tue, 27 Jan 2026 16:16:12 GMT

Stormwater runoff is a significant contributor of phosphorus (P) loading to waterbodies around the world. Green stormwater infrastructure (GSI) that uses filtration media, such as bioretention, can effectively retain suspended solids and associated particulate P, but is commonly less effective for soluble P retention. The addition of aluminum-based drinking water treatment residuals (DWTRs) may increase P-sorbing capacity of GSI media, though guidance is needed for material selection and to reduce risk of potential contamination. This study examined the P removal capacities of DWTRs (n=11) from drinking water treatment plants in the New England region (northeastern USA). DWTRs were compared for P-sorption potential using batch isotherm and column experiments and characterized for several material properties as well as arsenic leaching and per and polyfluoroalkyl substances (PFAS) content. Results indicate that P retention capacity of DWTRs is generally high (>1,000 mg P kg−1) but varies by approximately one order of magnitude. Lower DWTR bulk density and greater oxalate-extractable Al + Fe were correlated with greater P retention in column experiments. Our findings also indicate that the potential for significant arsenic leaching is low. PFAS were detected in 36% of DWTRs, often at low levels near the method detection limit, with three DWTRs having higher levels of certain PFAS. The addition of DWTRs to GSI is promising for enhanced soluble P removal on a decadal scale (10–90 years), but additional research on As, PFAS, and other contaminants should be pursued prior to use, especially in areas with known or suspected source water contamination. Achieving effective long-term P removal requires selecting DWTRs with favorable material properties (e.g., drier, lower bulk density, greater oxalate-extractable Al + Fe), and mixture with sand at up to 10% DWTR by volume and potentially higher if proven to not impede hydraulic conductivity. Field monitoring of DWTR-enhanced infrastructure at multiple time points postinstallation (e.g., years 1, 5, 10, 20, and 30) is needed to confirm P removal longevity over expected infrastructure lifespans.

Field Performance of an EcoVault Facility for Stormwater Quality Treatment

Fri, 09 Jan 2026 16:25:45 GMT

As urbanization accelerates, stormwater management in cities has shifted from focusing strictly on water quantity to addressing water quality. Traditionally implemented systems, such as stormwater ponds, while offering effective solutions, often require large land areas to implement, making them impractical for dense urban environments. Underground stormwater systems, like EcoVault, offer a more compact solution; however, they lack scientific studies under real-world conditions to prove their effectiveness in treating pollutants. This study evaluates the treatment performance of two parallel EcoVault systems with the same design, consisting of a sedimentation step and a filtration step. These facilities were retrofitted into two different stormwater sewer networks draining two urban catchments. The systems were assessed for their ability to treat total suspended solids, metals, nutrients, and organic pollutants from urban runoff. Over 15 rain events, the average total suspended solids (TSS) removal rate was 40% for EcoVault A and 46% for EcoVault B. The removal rates for metals varied, with EcoVault B showing better performance for average metal treatment (53% for Cu and 58% for Zn). However, neither EcoVault system removed dissolved metals, often with an increase of dissolved metal concentration in the effluent. The filtration step did not contribute to pollutant treatment, likely due to clogging and high hydraulic loading rates. The study highlighted the potential of underground stormwater treatment in areas with limited space availability, while identifying challenges such as treatment of dissolved pollutants.

Temperature Dynamics of a Rock Swale and Bioretention Green Stormwater Infrastructure System Treating Runoff from an Elevated Highway Interchange

Fri, 09 Jan 2026 16:25:45 GMT

A growing number of urban surface waters are impaired for high temperatures due to the heat exchange that occurs between the warm urban land surface and stormwater runoff before it enters downstream waterbodies. Green stormwater infrastructure (GSI) has the potential to reduce runoff temperatures; however, it is unclear how specific treatment approaches, such as rock swales, or sequencing of GSI in series can most effectively mitigate temperature in stormwater runoff. The objective of this study is to capture the temperature dynamics of a GSI treatment train consisting of rock swales leading to bioretention that captures runoff from an elevated highway interchange in Milwaukee, WI. Temperature was observed continuously during 17 runoff events at nine locations, including the primary influent from overpass downspouts, rock swale effluent, bioretention media, and bioretention underdrain effluent. Results indicate that rather than mitigate temperature, rock swales warmed runoff to a greater degree than that of highway overpass decks. However, the sequencing of bioretention practices at the end of the GSI system resulted in temperature reductions of 0.9°C–2.4°C on average to levels below thresholds for downstream trout species. Overall, this study demonstrates the importance of effective sequencing of GSI practices for effective temperature mitigation, which is a leading water body impairment in many states in the United States.

Development of a Novel Trash Capture Device for Highway Environments

Fri, 09 Jan 2026 16:25:45 GMT

Traditional trash capture devices that can be installed in upstream locations such as storm drains or curb inlets are of limited use in highway environments due to potential flooding, hydroplaning, safety, and maintenance-personnel exposure issues. There is a need for a trash capture system that can be retrofitted easily into existing highway drainage infrastructure or included in newer projects. To address this issue proactively, the California Department of Transportation (Caltrans) Division of Environmental Analysis (DEA) initiated a trash capture device development and testing project in early 2020. The DEA Stormwater staff developed the initial idea for a capture housing device. Computational fluid dynamics modeling was used first to assess the feasibility and performance. Next, the hydraulic capacity, trash capture characteristics, operation, and ease of maintenance were tested using a full-scale physical model. After successful testing, standard plans and design guidance were developed. The full-scale model physical test demonstrated the following: (1) the device can pass the 1-year, 1-h storm intensity specified in the regulations without overflowing or causing roadway flooding; (2) the device can pass the 25-year 5-min-duration return period storm drain system design storm event without causing roadway flooding; (3) the device will trap trash sizes of 5 mm or larger for the 1 year, 1-h storm intensity specified in the regulations; and (4) the device has the storage capacity for the quantity of trash generated from a typical 0.405 ha (1-acre) highway drainage area.

Understanding Long-Term Stormwater Best Management Practice Maintenance Challenges: Insights from the Virginia Department of Transportation

Fri, 17 Oct 2025 16:38:23 GMT

Best management practices (BMPs) are designed to manage stormwater and reduce pollution, but their effectiveness and compliance with regulatory requirements depend on consistent maintenance. Despite their importance, there is limited research on how stormwater practitioners allocate resources and navigate operational challenges to maintain BMPs under regulatory and budgetary constraints. To address this knowledge gap, this study conducted an open-ended survey of stormwater professionals across eight districts of the Virginia Department of Transportation (VDOT). Paired with a review of 17,874 BMP inspection records from 2020 to 2024, the survey data provided insights into how reported maintenance issues from surveys align with inspection-based observations of BMP conditions, how resource constraints shape maintenance priorities, and which strategies may improve long-term maintenance outcomes. Thematic comparisons between survey responses and inspection data revealed strong alignment for sediment and vegetation concerns but underreporting of erosion and structural issues in narrative responses. The findings also show how resource limitations, such as insufficient staffing, lack of flexible funding mechanisms, and administrative burden, lead districts to make trade-offs when addressing corrective and urgent maintenance tasks. Districts employed a variety of strategies to mitigate these constraints, including severity-based repair prioritization and creative use of roadside or compliance-linked funding. The study further highlights how institutional structures, such as the presence of a dedicated stormwater manager or the design of contractor agreements, significantly influence maintenance outcomes. Enhancements to VDOT’s geospatial BMP database are proposed as a way to centralize the system to streamline task bundling, prioritize repairs, and enhance cross-district coordination. By analyzing district-level adaptations, this study highlights practical approaches for maintaining stormwater BMPs despite limited resources.

Characterization of Foamed Glass Aggregate for Stormwater Management

Fri, 19 Sep 2025 08:58:23 GMT

Foamed glass aggregate (FGA) is a recycled lightweight material that has been widely used in a variety of infrastructure applications. However, a lack of understanding of basic hydraulic and environmental properties of the aggregate has limited usage in stormwater infrastructure, where FGA may offer water retention and contaminant removal benefits. This study utilized custom-built column and box testing to evaluate the hydraulic and environmental performance of FGA for stormwater applications. Two inflow solutions were used, including tap water and synthetic stormwater. Results of the study found that FGA has a high capacity for water storage and drainage (e.g., drainage rates of 0.62 to 3.26 cm/s), with a field capacity similar to sand and drainage similar to coarse aggregate. This enables water retention, which may be advantageous in green stormwater infrastructure designs relying on evapotranspiration for runoff reduction. Additionally, the porous surface structure of FGA was found to capture sediment suspended in stormwater inflow.

Coarse Biochar Improves the Hydraulic Performance of Compacted Roadside Soil Media

Thu, 18 Sep 2025 09:18:19 GMT

Compacting engineered soil media is necessary to ensure its stability in many urban contexts, such as in road embankments. However, compaction can reduce infiltration rates, increase runoff volumes, and impede vegetation growth. Amending soil media that is to be compacted by mixing it with biochar may largely mitigate the consequences of compaction, effectively helping road embankments and similar areas function as green stormwater infrastructure. Here, the authors report the results of a lab experiment intended to determine how biochar particle size and application rate influence the hydraulic properties of compacted roadside media. Specifically, the authors amended a loamy sand collected from the field with biochar ranging from 0 to 6% (w/w) and that was either unsieved or sieved to remove most coarse particles. The addition of biochar with many coarse particles (>2 mm) improved the saturated hydraulic conductivity (Ksat) of the medium postcompaction, but this effect diminished at biochar dosages above 3% (w/w). In contrast, the addition of biochar with few coarse particles did not improve Ksat postcompaction. These changes likely arose because unsieved biochar facilitated the addition of interconnected pores and did so to a greater extent than particle breakage led to pore restriction. Also, biochar addition improved water retention in the plant available suction range postcompaction, whether the biochar was sieved or unsieved. Amendment with relatively coarse biochar could therefore help compacted roadside soil media manage stormwater while also reducing plant water-stress in a frequently water-limited setting.

Quantifying the Water Quality and Hydrologic Benefits of Two Bioswales Receiving Highway Runoff in North Carolina

Mon, 19 May 2025 09:11:29 GMT

Bioswales are an emerging stormwater control measure (SCM) used to treat runoff from highways and parking lots. This SCM consists of an engineered media, gravel layer, and underdrain system beneath a vegetated channel, which helps to promote exfiltration while conveying runoff. This study evaluated how well two bioswales (BS2 and BS4) retrofitted with check dams mitigated stormwater runoff from a highway in Wake County, North Carolina. Inflow, overflow, and underdrain water quality and quantity data were collected using automated sampling equipment and weirs or estimated using runoff equations. Exfiltration was estimated as the difference between inflow and the sum of overflow and underdrain discharge. Outflow was calculated by summing the overflow and underdrain volumes at each time step. BS2 and BS4 were monitored for 61 and 53 storm events, respectively. Of those events, BS2 and BS4 exfiltrated 13 and 23 storms, respectively. For small storms (<19 mm), the mean percentage of runoff that was exfiltrated by BS2 and BS4 was 73% and 85%, respectively. There were also significant (α=0.05) differences between the bioswales’ inflow and overflow, underdrain, or outflow runoff volumes and peak discharges. These results suggest bioswales with check dams can manage stormwater. The mean total nitrogen overflow, underdrain, and outflow concentrations for BS2 were 0.84, 0.66, and 0.70 mg/L, respectively, and 2.10, 1.53, and 1.75 mg/L, respectively, for BS4. The mean total phosphorus overflow, underdrain, and outflow concentrations for BS2 were 0.16, 0.11, and 0.12 mg/L, respectively, and 0.44, 0.26, and 0.35 mg/L, respectively, for BS4. None of the concentrations were significantly different, limiting conclusions that can be drawn from this study.

Characterizing Stormwater Basin Conditions Using Tracked BMP Inspection and Rating Reports from the Virginia Department of Transportation

Tue, 18 Feb 2025 08:57:01 GMT

Studies have rarely used stormwater best management practice (BMP) condition rating data to quantify changes in condition ratings and characterize condition issues, making it challenging to implement proactive maintenance practices. To help address this knowledge gap, the authors answer the following questions pertaining to a widely used stormwater BMP: detention and retention basins. (1) How often do basin condition ratings change over time? (2) What are specific site and structural condition issues identified during condition inspections? (3) What issues and site characteristics correspond with basins that experience a rapid decline in condition rating, meaning a decrease in two or more condition rating levels within a single year? The authors do this by characterizing basin condition ratings and associated issues using information included in more than 5,500 basin inspection reports, each containing more than 200 questions, stored in the Virginia Department of Transportation (VDOT) asset management system. On average, between 5.6 and 8.3 issues were recorded per visit for D-rated and E-rated basins compared with 0.03 to 1.8 issues for A-rated and B-rated basins. Of the 901 basins with three consecutive years of inspections, 41% and 35% had condition ratings that changed from 2020 to 2021 and from 2021 to 2022, respectively. The most common issues associated with rapid condition rating decline included major corrosion on the low flow orifice trash/debris rack, control structure, and pipe. Rapidly declining condition ratings were observed in 67% of VDOT’s nine independent management districts, suggesting rapid declines occur independently of management practices. Higher median elevation and percent slope attributes and lower median population were correlated with basins experiencing rapid condition rating decline. Using these results as context, the authors discuss considerations for improving BMP inspection data quality and opportunities for supporting proactive BMP management practices that can benefit other agencies managing a large portfolio of stormwater assets.

Green Infrastructure in Series to Treat Stormwater Runoff from a Highway Overpass

Mon, 23 Sep 2024 09:07:13 GMT

Green stormwater infrastructure (GSI) is effective at capturing and treating runoff from impervious traffic areas, including roadways, parking lots, and pedestrian walkways; however, its application in treating highway or overpass runoff presents unique challenges due to the high energy of influent flows and high pollutant concentrations. Therefore, it is unclear how these challenges might affect their ability to capture and treat runoff. The objective of this study was to evaluate the performance of a GSI system that treats stormwater runoff from a highway overpass in Milwaukee, Wisconsin. Stormwater runoff was captured at three sampling locations throughout the system, including (1) the primary influent from a highway overpass downspout entering a rock swale, (2) the effluent of the rock swale before it enters a bioretention system, and (3) the bioretention underdrain representing the system’s effluent. These samples were then tested for total suspended solids, total phosphorus, dissolved reactive phosphorus, and total coliforms. Results indicated that the rock swales were effective at reducing mean concentrations of total suspended solids (72%) and total coliforms (59%) from the primary influent. Results also indicated that the entire system, composed of rock swale and bioretention treatment was effective at reducing mean concentrations of total suspended solids (80%), but less so for mean concentrations of total phosphorus (16%) and total coliforms (3%) from the primary influent. These outcomes demonstrate that GSI treatment trains can mitigate total suspended solids and total phosphorus from highway overpass runoff, while site-specific hydrological conditions and GSI designs may influence the amount of highway overpass runoff pollutants that are mitigated.

Promoting Autonomous Vehicles Using Travel Demand and Lane Management Strategies

Wed, 22 May 2024 16:59:41 GMT

A key challenge facing cities of today is the persistent and growing urban congestion that has significant adverse effects on economic productivity, emissions, driver frustration, and quality of life. The concept of smart cities, which can revolutionize the management of metropolitan transportation operations and infrastructure, shows great promise in mitigating this problem. Specifically, the automation and connectedness (A&C) of smart city entities such as its infrastructure, services, and vehicles, can be helpful. In this regard, this paper focuses on the potential of autonomous vehicles (AVs) and AV infrastructure, particularly during prospective transition era where there will be mixed streams of AVs and human driven vehicles (HDVs). The paper considers two aspects of this potential: connectivity-enabled travel demand management and travel infrastructure supply through lane management. To demonstrate the opportunity associated with this potential, this paper first presents an AV-enabled tradable credit scheme (TCS) tomanage travel demand. Here, the transportation authority distributes travel credits to travelers directly and instantaneously using the AV’s A&C features. Travelers use their A&C features to pay these credits for travel at specific locations or times-of-day according to their choices of lane types and links. With regard to supply, this paper considers that the road network consists of two lane types: AV-dedicated, and mixed traffic lanes, and develops a scheme for travel demand and lane management strategies in the AV transition era (TLMAV). Firstly, the paper models the expected travel choices based on user equilibrium concepts, at different levels of AV market penetration. Then, the existence of the optimal solution in terms of link flows and the prevailing travel credit price is demonstrated. Then the paper establishes the optimal TLMAV that minimizes total travel time subject to user equity constraints. The results demonstrate the extent to which HDV users will suffer an increase in travel cost if equity is not considered in the model. The results also show how the transportation agency can use TLMAV to keep HDV travel costs to acceptable levels, particularly during the early stages of the AV transition period. Further, the paper shows how TLMAV could be designed to gradually diminish inequity effects so that travelers, in the long term, are motivated to shift to AVs.

Hydrologic Performance of Vegetated Compost Blankets for Highway Stormwater Management

Wed, 15 May 2024 10:11:33 GMT

In an attempt to reduce the impacts of stormwater, stakeholders are exploring ways to improve the performance of existing stormwater control measures adjacent to highways, including vegetated filter strips (VFSs). This study assesses the hydrologic performance of a VFS amended with a vegetated compost blanket (VCB) through evaluation of dynamic flow modification, event volume storage, and cumulative performance. Over 2.25 years, 278 rainfall events were observed at a highway median in Maryland for two VCBs of 7.6-cm depth and 30-m width along the highway, one at 3-m length and one at 6-m length. Supplemental greenhouse mesocosm experiments provided supporting information on stormwater storage and slope impacts. VCBs were found to significantly reduce both stormwater flow and volume. Peak flows were significantly reduced by 39% for the 3-m and 72% for the 6-m VCB in comparison to highway runoff. At the highest flowrates, both VCBs were unable to significantly reduce flow, and instead acted as conveyance. Total influent stormwater volume capture over the entire study period was found to be 44% and 55% for the 3-m and 6-m VCBs, respectively. A useful design estimate for representative storage capacity, using saturated moisture content and wilting point of the media, was determined through use of a hockey-stick fit for inflow-outflow curves. Improvements in VFS soil hydraulic properties and vegetative cover over the course of the experiment were observed, indicating additional mechanisms for hydrologic improvement.

Tradeoffs Between Safe/Comfortable Headways Versus Mobility-Enhancing Headways in an Automated Driving Environment: Preliminary Insights Using a Driving Simulator Experiment

Fri, 15 Mar 2024 16:35:11 GMT

The anticipated benefits of connected and autonomous vehicles (CAVs) include safety and mobility enhancement. Small headways between successive vehicles, on one hand, can cause increased capacity and throughput and thereby improve overall mobility. On the other hand, small headways can cause vehicle occupant discomfort and unsafety. Therefore, in a CAV environment, it is important to determine appropriate headways that offer a good balance between mobility and user safety/comfort. Design/methodology/approach - In addressing this research question, this study carried out a pilot experiment using a driving simulator equipped with a Level-3 automated driving system, to measure the threshold headways. The Method of Constant Stimuli (MCS) procedure was modified to enable the estimation of two comfort thresholds. The participants (drivers) were placed in three categories (“Cautious,” “Neutral” and “Confident”) and 250 driving tests were carried out for each category. Probit analysis was then used to estimate the threshold headways that differentiate drivers' discomfort and their intention to re-engage the driving tasks.