Sustainability + Transportation
Due to rising concerns about climate change over the past several years, environmental sustainability has become a significant consideration in almost every transportation project today. Developers, engineers, architects, and planners have a responsibility to commit to creating a built environment that reduces negative environmental impact.
In that effort, transportation engineers and planners usually seek to limit the number of single-occupancy vehicle trips to a given site and the city. They typically accomplish this by providing connectivity to public transportation and creating safe and comfortable spaces for pedestrians and cyclists to travel. Locally, DC’s Department of Energy & Environment affirms that “shifting our transportation system away from single occupancy vehicle trips towards walking, biking and using public transit is the best way to reduce our energy use in the transportation sector.”
In 2018, the Transportation sector accounted for 28% of United States Greenhouse Gas Emissions. Breaking down the contributions within transportation, Light-Duty Vehicles are the source for 59% of emissions. The EPA reports that “a typical passenger vehicle emits about 4.6 metric tons of carbon dioxide per year,” and producing and distributing the fuel to power vehicles creates additional greenhouse gases.
The transportation shift toward non-auto modes is met with several challenges including funding, , and accessibility. The first hurdle for many individuals is overcoming a reliance on automobiles as a primary mode of transportation. Transportation Statistics Annual Report 2020 found “households increasingly own more vehicles, with two- and three-vehicle households now comprising a larger share of the population.” One way that planners seek to reduce the number of single vehicle trips is through eliminating the mandatory vehicle parking requirements that most cities impose on new developments. An article from Bloomberg CityLab links cheap, excessive parking to drive-alone commutes, traffic congestion, and higher rents. To combat this, some cities are moving towards repealing mandatory parking requirements.
In Buffalo, the 2017 Green Code repealed all mandatory parking requirements (MPRs) in the city. In the years since it was enacted, “mixed-use developments in transit-rich locations along primary commercial corridors tended to provide fewer off-street parking spaces relative to preceding MPRs.”
Lifting parking requirements creates flexibility for addressing transportation needs. As opposed to minimums, DDOT recommends “preferred” parking maximums as part of the Comprehensive Transportation Review guidelines that large developments need to meet before gaining approval. Put simply, they argue that “if you plan and design for auto-oriented development, you’ll get high traffic generating development.” The maximums depend on building size, use, and proximity to transit. Buildings that have too much parking are required to provide additional Transportation Demand Management measures to reduce vehicle trips to the site.
In instances where parking is reduced, fewer people would be driving, likely utilizing alternative modes of transportation, lowering emissions, and moving towards more sustainable transportation.
A great alternative mode of transportation with zero emissions is the bicycle. Bicycles promote not only sustainability but also personal health and fitness. Many people turned to bicycles in the last year as an alternative to using public transportation during the COVID-19 pandemic.
A New York Times article from May 2020 reported, “the spike in sales comes on the heels of stay-at-home orders that have temporarily curtailed daily life, but that may permanently transform the role of bicycles into something more essential, including a safer alternative to public transit as the nation slowly begins to reopen.”
As more people took to cycling, cities responded with initiatives like DDOT’s Slow Streets and Car Free Lanes. Providing additional space for cyclists to move about the city safely might give reassurance to some still on the fence about trying cycling. While these things came about as a result of the pandemic, if they become permanent fixtures, the number of cyclists may continue to grow or at least hold steady at what’s been reported during the pandemic.
The same New York Times article cites Sarah M. Kaufman, Associate Director of New York University’s Rudin Center for Transportation Policy and Management, saying “The U.S. has been built around cars. The European model has tended to be more forward looking in terms of sustainability and safety, which leads them to favor bikes.”
We have seen DC, Arlington and other jurisdictions adopt Vision Zero plans in an effort to improve safety for cyclists and pedestrians. Vision Zero positions itself as “a fundamentally different way to approach traffic safety,” seeking to “eliminate all traffic fatalities and severe injuries, while increasing safe, healthy, equitable mobility for all.”
Moving commutes and local errand runs from trips made in vehicles to bicycles will help to cut down tailpipe emissions. Another option is shifting towards utilizing public transportation. The significant advantage to public transportation is the increase in passengers per trip using the mode of transportation. While a bus may produce more CO2 emissions than a vehicle, the bus can accommodate more passengers than a single car and thereby reduce the number of vehicles on the road concurrently.
Public transportation has also committed to improving sustainability efforts. The District’s public bus system, the Circulator, includes 14 fully electric vehicles in their fleet (DC Department of Energy & Environment). Washington Metropolitan Area Transit Authority (Metro) has committed to planning for a zero-emission fleet in their 2019 Energy Action Plan.
Parking, bicycling paths, pedestrian friendly spaces, and public transportation are all key considerations in creating and implementing Transportation Demand Management plans. TDM plans are created for buildings or developments to provide occupants with a comprehensive menu of transportation options for that area. The strategy considers bike and pedestrian choices, public transportation connectivity, carpooling, and telework programs to give users a range of transportation options. Providing these alternative modes of transportation may influence a move away from reliance on automobile trips to travel to/from the destination.
With updated guidelines and regulations coming from jurisdictions coupled with transportation demand management plans, transportation engineers and planners will continue to work in tandem with clients, developers, and governing bodies to move toward reducing transportation’s environmental impact on our communities.
References:
DC’s Department of Energy & Environment
Transportation Statistics Annual Report 2020
SideWalkTalk Buffalo Ended Parking Requirements
DDOT Guidance for Comprehensive Transportation Review in the District of Columbia
Tollbooth-style PUDO
Scramble-style PUDO
A scramble-style PUDO refers to when some (or all) students are being dropped off or picked up on the street, not an adjacent sidewalk, and walking between cars. For scrambles, some cars drive into a designated area, and then they all stop and don’t move again until all students arrive safely at the school or in their car at dismissal. Scrambles are often used during dismissal for schools with limited sidewalks since a scramble allows for more cars to load simultaneously.
Scramble-style PUDO
When helping plan a school, what does Gorove Slade recommend? In short, all of them. Our recommendation is to design a PUDO facility that can be flexible and work for several operational styles. Once up and running, the staff and teachers can try several and see what works best. The goal is to give them the tools they need to find the best solution.
An example is the new Cardinal Elementary School in Arlington, VA. We recommended a flexible system with ample sidewalks and a bypass lane, and once it was up and running, the facility operated a bit differently than planned. At dismissal, teachers split the facility in two, with two pick-up waiting spots – one for younger grades closer to the school and one for older ones further away. This allowed for quicker matching at dismissal times.
Afternoon pick-up at Cardinal Elementary School
PUDO Analysis
Gorove Slade handles the analysis of PUDO facilities in several ways. They are inherently tricky to analyze because some operational details are challenging to model, and the significant demand is very sensitive to variables leading to large ranges of results.
Here are three ways we approach analyzing PUDO:
Queuing Analysis/Equations
One method is to use classic queuing equations, which transportation engineers have used for decades for toll booths. They are based on three factors: the arrival rate of cars, the number of booths, and the processing speed of the toll. All three of these factors correspond to PUDO facilities.
Even so, queuing equations often fail to get accurate results for PUDO facilities. For example, we were working for a private school with a notorious PUDO problem at dismissal, so we went to the field and measured the arrival rate of cars, the number of vehicles that could load simultaneously, and the average time for each pick-up. We then entered that information into our queuing models, which then told us the queue should be negative, or in other words, there shouldn’t be a queue at all, as the car arrival rate was less than the overall number of cars that could be processed.
Subsequently, we returned to our observation notes and video. We realized the longest queue in the field was when dismissal began and that our model was correct in that the queue was being processed faster than additional cars arrived. Parents and guardians arrived so early that they stacked up well beyond the school property, but once dismissal started, the queue only got shorter as more cars showed up.
The lesson we learned here is that there are more factors in the queuing analysis than just the traditional three and that arrival rates are not random.
Comparable Analysis
A common transportation engineering practice is to study comparable locations, and sometimes, that works well for PUDO facilities, especially when queuing equations don’t work as described above. We’ve taken max queue data at several private and public schools. We can try to match the car length per student ratio from a site comparable to the one we’re working on, given the design and operational elements of their PUDO.
There are two issues with using comparable data. The first one is that there’s an extensive range of data, so using our observed data leads to a max queue range of 0.10 to 0.20 cars per student being picked up. The wide range is due to how well the PUDO processes traffic and the starting queue length. To use these ratios, you need to estimate how well the PUDO will operate within this range.
But more importantly, our observations found some schools with a max queue under the 0.10 cars per student range during dismissal. This wasn’t because they had fewer cars picking up students; it was because the cars weren’t all in the same place. For example, the school we observed once had around 25 to 30 cars picking up simultaneously, but only six were at the official pick-up spot at the front door. The others were in the parking lot or curbside in several locations. So, when planning PUDO facilities, the ability of parents to use informal locations near the school can be a huge factor in the max queues and overall PUDO operations.
VISSIM Modeling
When something other than engineering judgment combined with the two analyses stiles above is desired, we turn to detailed traffic models using the VISSIM software platform. VISSIM models are highly detailed and can account for things like starting queues and varying arrival rates. The main drawback is that they require more time and resources to assemble, and in the end, they still can’t arrive at a perfect representation of a PUDO since human behavior is always a factor.
Thoughtful design and operations can dramatically improve the pick-up and drop-off process. Whether planning a brand new PUDO experience or improving existing operations, the principles and methods discussed here provide a framework for tackling one of the most persistent logistical challenges for administrators and parents alike. By considering key factors like demand patterns, operational strategies, and facility types, schools can create systems that minimize queuing, reduce neighborhood impacts, and make the beginning and end of the school day better for all.
