Despite challenges, TSP is a bridging technology that can make immediate improvements
The transition from fossil fuels to zero-emission buses is already underway. The market is starting to converge on costs and implementations are growing, particularly in Europe.1
Major change is also on the horizon in the United States. The Biden administration has proposed $174B for electrification as part of the American Jobs Plan and Federal Transit Administration guidance on the topic signals that zero-emission transit vehicles are expected in the relative near-term.2 Still, there are more questions than answers at this point. Different states have different mandates on different types of low-emission technology.3
As with any change, there are major challenges that transit managers must navigate. In some cases, federal grants might cover the cost of buses, but not the cost of charging/refueling infrastructure. In other cases, operational questions remain about how to maintain these new vehicles. For electric systems, there could be a need for additional substations to power this charging infrastructure, further increasing the costs of operating these buses.
On top of all that, the U.S. America is still in a transition period, meaning there needs to be infrastructure for both fossil fuels and zero-emission technologies.
As frustrating as some of these challenges may be, technologies – including connected mobility solutions and transit signal priority (TSP) – can alleviate some of these pains by providing a measure of predictability to a transit system. Specifically, TSP can help to enable faster average travel times, less variability in acceleration and deceleration, and fewer full stops.
First, increasing the average travel speed along a route improves battery efficiency.4 Buses can travel longer distances without needing to recharge if they travel at faster speeds.
Second, rapid acceleration to “make the green” or braking hard to avoid running a red light are inefficient driver behaviors that deplete batteries (or hydrogen fuel cells) more quickly.4 Extending that to full stops at intersections, it takes much more energy to get a large vehicle like a bus moving after a stop, as compared to keeping that vehicle moving at a constant speed. TSP reduces the need to start and stop at intersections, enabling drivers to operate with less aggressive braking and acceleration.
Finally, the combination of constant speeds and removal of unpredictable stops comes to a head when vehicles get to charging stations. The predictability of TSP enables agencies to build recharge time into the schedule with more accuracy. If a bus needs 5 minutes of recharge time for example, the agency can build that time in, knowing that the bus will arrive on-time thanks to the predictability derived from TSP. This can help prevent delays from snowballing, because TSP will enable the bus to get back on schedule should it fall behind.
TSP is a bridging technology in the sense that it can provide immediate improvements for fossil fuel vehicles and can be applied in the future to new low-emission vehicles. Transit agencies do not need to wait for federal agencies or standards committees to develop guidance. It exists right now, and it’s been proven to work.5 Further, the technology is transferable as agencies’ vehicles change. This is especially true with software-based TSP, where new buses are made a part of the system and retired buses are removed.
As agencies plan for the low-/no-emission vehicle migration, TSP gives them control over how vehicles interact with the broader traffic network, ensuring more predictability along routes. Ultimately, TSP can improve rider confidence in the services being provided. Buses arrive at the posted times, allowing riders to get to work, school and back home to their families. Even as vehicle types, technologies and routes change throughout the system, delivering on that transit promise is critical to transit operations.
- The pandemic doesn’t stop the European e-bus market: +22% in 2020 (sustainable-bus.com)
- Low or No Emission Vehicle Program – 5339(c) | FTA (dot.gov)
- Alternative Fuels Data Center: State Laws and Incentives (energy.gov)
- Shefang Wang: Understanding the Energy Consumption of Battery Electric Buses in Urban Public Transport Systems (2020)