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Have you ever been on a Muni vehicle and realized that if the light had only stayed green for just a few more seconds you wouldn’t have been trapped at a red light? SFMTA’s Connected Corridor Pilot approached this problem with a new state of the art solution.
Most signals in San Francisco do not have sensors to detect vehicles at an intersection. However, through a grant from the U.S. Department of Transportation, our project team was able to test an advanced technology for signal timing based on who is present at an intersection. In this way, transit platform and traffic signal sensor data can be used to activate signal timing adjustments, responding to traffic conditions in real time. These adjustments provide more opportunities for transit vehicles to make it through intersections on a green light.
The project team turned on the adaptive signal timing program during several days in July and August 2021, with traffic engineers and traffic signal electricians monitoring intersections both in-person and by observing traffic cameras. Our priority was to reduce transit vehicle travel times. Once in place, we compared travel times for trains both before and after the new technology was implemented.
We found that with our pilot project, the average light rail vehicle (LRV) travel time along the 1-mile corridor was reduced by 66 seconds, resulting in an average travel speed increase of 21% from 8.2 miles per hour (MPH) to 9.9 MPH. With this system, the chance that a train will reach an intersection on a green light improved from 62.1% to 85.8%, meaning almost no red-light delay.
Figure 1. Pilot Corridor Performance, Before and After Comparisons
During the pilot, 60% of LRV corridor trips had 10 seconds or less of red-light delay, compared to only 5% previously. In fact, 20% of trains saw no red-light delay at all on the corridor, compared to the previous study period when not a single train avoided red light delay entirely.
Improving signal timing for just one specific mode or direction can potentially result in negative impacts for others. To evaluate this, we measured travel impacts to pedestrians and non-Muni vehicles to evaluate the potential effects from prioritizing transit. Fortunately, our data show that there was a 1% increase in the overall odds that other vehicles would encounter a green light and only a 1% increase in the odds that pedestrians would reach an intersection on a Do Not Walk symbol.
Vehicles on side streets were generally unaffected unless they were also held to prioritize train through traffic. Heavier volume side streets such as Mariposa Street had increased average wait times of up to 78% for vehicles, from an average wait of 46 seconds previously, to an average wait of 87 seconds during the pilot. Fortunately, the adaptive signal system only increased the average wait time by 4 seconds for pedestrians if they arrived on a Do Not Walk symbol, from 22 seconds to 26 seconds. Further refinement of the signal timing logic could help address these concerns.
With detailed information collected through the advanced sensors, our project team was able to make refinements and real-time signal timing adjustments that account for time of day, direction of travel, and the real-time volume of pedestrians, vehicles, and transit vehicles.
These promising results will lead the SFMTA to consider applying this technology in other locations to better understand how the system could work more widely around the city and any trade-offs that could arise in regard to overall traffic flows.
Looking forward, we are also exploring other new technologies. For example, the LiDAR (sensors that use lasers to identify objects) used in this project provides a new way to capture and classify objects at intersections, but there may be a need for additional sensors or different mounting locations to improve detection accuracy. Project staff will build upon the lessons learned from the pilot to inform future efforts to optimize the signal timing to make our streets better for all users.
From just a few stretches of scattered lanes in 2013, San Francisco’s protected bike network now stretches like a green web connecting more and more of the city. See how much has changed over the last eight years:
In just the blink of an eye, San Francisco has become one of the most bike-friendly cities in the U.S. To date, San Francisco has 464 miles of bikeways, including:
As we’ve expanded the network of safer bicycle routes through San Francisco, more people are choosing to ride bicycles for recreation and transportation every year. Since 2006, travel by bicycle has grown by 184 percent citywide. Before the COVID-19 pandemic, bike counts hit an all-time high: in 2019, approximately 52,000 bicyclists were observed at 37 locations during peak periods, a 14 percent increase from the previous year.
Creating safe bicycling routes throughout San Francisco is imperative for reaching the city’s Vision Zero goal of eliminating traffic deaths and reducing severe injuries—and also for encouraging more people to choose to travel by bike. In the last several years, the SFMTA dramatically accelerated installation of safe bicycling infrastructure. In 2019, Mayor London Breed committed to doubling the rate of bike lane construction in the city from an average of five miles per year to 20 miles over the following two years. That same year, the SFMTA launched its Vision Zero Quick-Build program to roll out safety improvements, including protected bike lanes, along the city’s High Injury Network. Compared to more intensive capital projects that can take years to complete, quick-build projects can transform a street in a matter of weeks or months. See that jump in bike infrastructure after 2019? Quick-Builds were behind a lot of it.
COVID-19-related street transformations were also part of the reason behind the most recent increases in bike infrastructure. While the pandemic posed a number of challenges for the city, bike route planning, design and construction took off! With the addition of Slow Streets and car-free streets like JFK Drive, the city’s bike network grew by approximately 50 miles and increased connectivity between many of San Francisco’s neighborhoods. While these street transformations were introduced as part of an emergency response, we are exploring ways to establish them as permanent parts of San Francisco’s streetscape and bike network.
Looking to the future, as part of the 2021 Vision Zero Action Strategy, the SFMTA is committing to create a citywide, completely connected Active Transportation Network that includes bike lanes, Slow Streets, and car-free/car-light streets. We’re excited to keep building on last eight year’s bike network progress, adding even more green lines to the San Francisco map.