Intersection Design to Accommodate ADA Curb Ramps: Raised Crosswalks/Crossing Islands

Furth. Tahmasebi. Crossing islands at unsignalized intersections, in addition to their pedestrian crossing safety benefits, can also serve as speed control chicanes by forcing vehicles to make a reverse curve. A method is developed for determining the chicane length (and thus, parking setback) needed for a two-lane road for a given lane width, island width, and target speed, based on models of the relationship between road geometry vehicle path radius, and speed. New data on the speed–radius relationship is presented. The concept of “informal flare” is also introduced; it is a common approach geometry that allows a left-turning vehicle to wait for a gap in opposing traffic without blocking through traffic behind it. Using informal flares can make it possible to prevent left-turn blockage without sacrificing a crossing island for a left-turn lane. Curb continuation lines at median openings are presented as a means to enhance informal flare function. Original data are presented relating informal flare function (the tendency of through vehicles to bypass a waiting left-turner) to a road’s half-width. Geometric analysis shows that intersections with crossing islands can fit on roads with right of way as narrow as 60 ft, and with curb-to-curb width as narrow as 40 ft, while still accommodating turning school buses and bike facilities and preventing left-turn blockage. Various performance measures are used to evaluate intersection geometry, including measures related to through vehicle speed, turning vehicles, and pedestrians. With crossing islands, pedestrian safety with respect to left-turning vehicles is substantially improved as the turning path becomes square to the crosswalks, making the vehicle path more predictable and reducing vehicle speed, conflict area size, and pedestrian exposure distance.

Fipke, Symons. Nanaimo has been developing its Complete Street Design Guideline while in parallel putting it into practice on the Metral Drive corridor, showcasing sustainable urban transportation design in the City. The guidelines set a high bar for all future street design, reallocating the right-of-way in an equitable manner and managing conflicts safely. The immediate implementation of the guidelines on Metral Drive will demonstrate how such designs can contribute to community wellbeing by providing a safe environment that enables people to choose active and healthier travel options while also enhancing the streetscape. Metral Drive currently has varying levels of pedestrian provision from sidewalks to gravel shoulders and no cycling provisions. The inconsistencies are not conducive to attracting people out of their cars. Using the guidelines to develop the Metral Drive detailed design, the City will provide people, regardless of their age, income or physical ability, with safe travel options to the Woodgrove Centre, one of Nanaimo’s key mobility and economic hubs. While the guideline recommends best practice levels of space and separation, it also includes retrofit guidance and speaks to how similar outcomes can be achieved for lower costs or in constrained rights of way. The guideline and Metral Drive design include many best practices, but most innovative is the adoption of Dutch design principles prioritizing active modes through design with continuous sidewalks and bike paths across local roads. While this old design technique is often used in Europe, we believe it has not been fully implemented in Canada. To understand the value this would add to the Canadian context and confirm our belief that this technique has not been widely adopted, the team queried many well-respected planners, engineers, and advocates through twitter to try and find examples of such designs. It revealed nobody in Canada appears to be adopting such designs and Nanaimo aims to change that! Metral Drive will provide a Canadian showcase for Dutch-style intersections in Canada prioritizing the safety of our most vulnerable and will position Nanaimo as an example of best practice for all communities in Canada to reference.

Blewden, Mackie, Thorne. The purpose of this report is to provide clarity around the design and operation of raised safety platforms and deepen understanding of leading international practice across a range of applications and performance dimensions. A review of literature and sample site investigations have found that a community of practice around raised safety platforms at arterial signalised intersections is emerging and that installations to date are reducing traffic speed and therefore should improve safety in line with overseas literature. Minor design and construction inconsistencies should be addressed, and any reported issues should be investigated within the context of Safe System performance. A range of new and innovative raised safety platform applications in rural and urban contexts also look promising.

Chimba, Mbuya. This study assessed the impact of traffic calming measures to the speed, travel times and capacity of residential roadways. The study focused on two types of speed tables, speed humps and a raised crosswalk. A moving test vehicle equipped with GPS receivers that allowed calculation of speeds and determination of speed profiles at 1s intervals were used. Multi-regime model was used to provide the best fit using steady state equations; hence the corresponding speed-flow relationships were established for different calming scenarios. It was found that capacities of residential roadway segments due to presence of calming features ranged from 640 to 730 vph. However, the capacity varied with the spacing of the calming features in which spacing speed tables at 1050 ft apart caused a 23% reduction in capacity while 350-ft spacing reduced capacity by 32%. Analysis showed a linear decrease of capacity of approximately 20 vphpl, 37 vphpl and 34 vphpl when 17 ft wide speed tables were spaced at 350 ft, 700 ft, and 1050 ft apart respectively. For speed hump calming features, spacing humps at 350 ft reduced capacity by about 33% while a 700 ft spacing reduced capacity by 30%. The study concludes that speed tables are slightly better than speed humps in terms of preserving the roadway capacity. Also, traffic calming measures significantly reduce the speeds of vehicles, and it is best to keep spacing of 630 ft or less to achieve desirable crossing speeds of less or equal to 15 mph especially in a street with schools nearby. A microscopic simulation model was developed to replicate the driving behavior of traffic on urban road diets roads to analyze the influence of bus stops on traffic flow and safety. The impacts of safety were assessed using surrogate measures of safety (SSAM). The study found that presence of a bus stops for 10, 20 and 30 s dwell times have almost 9.5%, 12%, and 20% effect on traffic speed reductions when 300 veh/hr flow is considered. A comparison of reduction in speed of traffic on an 11ft wide road lane of a road diet due to curbside stops and bus bays for a mean of 30s with a standard deviation of 5s dwell time case was conducted. Results showed that a bus stop bay with the stated bus dwell time causes an approximate 8% speed reduction to traffic at a flow level of about 1400 vph. Analysis of the trajectories from bust stop locations showed that at 0, 25, 50, 75, 100, 125, 150, and 175 feet from the intersection the number of conflicts is affected by the presence and location of a curbside stop on a segment with a road diet.

Makwasha, Turner. A recently concluded Austroads study identified effective and innovative countermeasures for improving safety outcomes on urban arterial roads. Included in the study were raised platforms at priority controlled intersections (raised intersections), midblock and pedestrian crossings (wombat crossings). While these treatments have been widely applied overseas and, to an extent, across Australia and New Zealand (especially wombat crossings and at midblock sections on local and collector roads), a measure of effectiveness in mixed use and high volume environments in an Australian context was required. Using available speed and crash data from across Australia, this paper applied Poisson regression analysis in a retrospective quasiexperimental study to determine the effect of raised platforms on crash occurrence and severity. The results showed that overall, raised platforms are effective in improving road safety on urban roads. The effectiveness differed by platform type; platforms were most effective in reducing casualty crashes at wombat crossings. Casualty crashes fell by 63% at wombat crossings, 47% at midblock platforms and an indicative 55% reduction at priority controlled intersections. Furthermore, 85th percentile speed reductions of between 5 km/h and 8 km/h were observed at the different platforms. While this study provides an effectiveness measure for raised platforms on urban roads in Australia, most sites were high order collector roads. Further work is required to determine when and where on the urban arterial network platforms are most and/or least effective, the effect of design and implementation considerations on effectiveness and overall effectiveness in different conditions and different road users.

Pratt, McGarrigle, Turner. It will be very difficult to achieve a perfectly Safe System on our road network (i.e. zero fatalities or serious injuries) without the introduction of new and innovative road infrastructure treatments. There are treatments that exist overseas and have proven effectiveness; however the uptake of these solutions in Australia has been limited in many cases. This is due to a number of issues, including lack of knowledge on their use and effectiveness, lack of experience with design and implementation, and risk aversion. This paper will discuss issues relating to the future uptake of innovative infrastructure solutions through the case study of raised Safety Platforms on approach to signalised intersections on arterial routes – a new road infrastructure treatment that VicRoads has been in the process of researching, trialling and implementing on Victorian roads. The aim of this treatment is to achieve Safe System vehicle speeds through intersections (50 km/h). Although this infrastructure is used extensively overseas (e.g. in the Netherlands), it has yet to be introduced on arterial roads in Australia. ARRB undertook a comprehensive literature review on the likely benefits of these treatments, performed trials to establish vertical accelerations and driver comfort levels in a variety of vehicle types and performed modelling to assess the effects of road slope on effectiveness. VicRoads is currently in the process of installing the raised Safety Platforms at an intersection near Geelong, Victoria, and is due for completion in July 2015.

King, Carnegie, Ewing. Documentation was done on the effect of a raised median, signalized and redesigned intersections, curbs, and sidewalks on vehicle speed, pedestrian exposure risk, driver predictability, and vehicle volume along a four-lane suburban roadway in central New Jersey. The analysis used both quantitative tools (speed and volume counts, timing runs) and qualitative methods (pedestrian tracking, video, before-and-after photography). The results are that the 85th-percentile vehicle speed fell by 2 mi/h and pedestrian exposure risk decreased by 28%. Also, the median allows pedestrians to cross one direction of traffic at a time and signals, curbs, median, redesigned intersections, and striping patterns work together to manage driver behavior. In regard to vehicles, it was found that vehicle volumes were not affected and that vehicle speeds acted independently of vehicle volumes. A collision analysis projected a savings of $1.7 million over the next 3 years in direct and indirect costs. The goal of the report was to produce a simple and straightforward analysis tool for similar projects in the area. Some of the benefits of roadway projects such as these can be quantified numerically, whereas others rely on qualitative analyses. For example, before-and-after speeds are easily gathered and compared, whereas before-and-after pedestrian behavior at the raised median requires a more in-depth approach made easier by digital cameras. Together, before-and-after data and before-and-after imaging present a more holistic picture of the benefits and limitations of a project.