Our Climate Crisis puts CO2 reductions at the top of environmental concerns. The transportation sector especially needs electrification for most of what we currently do using fossil fuels. In a world of limited resources, we must also consider "ephemeralization", Buckminster (Bucky) Fuller's word for achieving the same or more output (products, services, information, etc.) while requiring less input (effort, time, materials, resources, etc.). In the case of PRT, light-weight cabs lead to light-weight guideways - both of which result in reduced material and energy requirements. Beyond primary and secondary CO2 reductions, PRT promises additional environmental/nature benefits.
Reducing Fossil Fuel Pollution
What if Global Warming causes society to crash before we can start exponential growth of carbon-reducing technologies like PRT? While our Climate Crisis presents a challenging problem, Personal Rapid Transit (PRT) offers a fresh, out-of-the-box solution that is networked, scalable, and replicable. In short, it could spread rapidly enough to change the course of our future.
While transportation accounts for a large percentage of CO2 emissions globally, it hits 59% in Milpitas, California. Electrified PRT can substantially reduce those emissions. Rather than electrify privately-owned cars that sit idle most of the time, PRT electrifies a high-use, community-shared transit cabs that offer low-cost, convenient, and quick trips within its service area.
The above graphic from “Comparing the Carbon Footprint of Transportation Options" shows the carbon footprint of transportation options in grams of carbon dioxide (CO2) equivalents emitted per person to travel one kilometer (CO2e/pass-Km). Clearly, PRT stands out among the options.
Another way to estimate CO2 reductions for various transit modes is by comparing their energy consumption. For example, kW-hr/pass-mile is used in the ENERGY USE bar chart on page 23 of the ITNS Business Plan. The list of various transit modes shows PRT near the bottom with 0.6 kW-hr/pass-mile, and Light Rail at 3.0 kW-hr/pass-mile. PRT company Glydways estimates an average of 0.18 kW-hr/mile for their cabs.
PRT's low energy consumption results from the highly efficient, non-stop trips provided by PRT that use about 90% less energy than cars. By using linear induction motors to move cabs rather than fossil-fueled combustion engines, PRT can use increasingly common carbon-free, renewable energy.
The reduced amount of power/electricity required to run a light-weight, demand-responsive PRT system rather than a heavy, scheduled one represents a profound shift from fossil fuel-based mass transit systems that run regardless of need.
The energy-use charts above are on page 30 of Dr. J. Edward Anderson's document, What Determines Transit Energy Use, from the Journal of Advanced Transportation, 22:2 (1988), pp. 108-132. The chart on the left shows Electrical Energy Use that ranges from 130 Watt-hrs/passenger mile at 15 mph to 650 Watt-hrs/pass-mile at 60 mph. On the right is a chart showing the miles-per-gallon-equivalent for PRT speeds ranging from 15 mph (118 mpge) to 60 mph (30 mpge).
In short, PRT uses far less energy/fossil fuel than other transit options, which leads to ...
Gigaton Reductions in Carbon Emissions
To estimate the magnitude of CO2 reductions possible with PRT, let's use a shorthand “unit” of 100 square miles of PRT service. Each unit costs about $7B, and can abate an estimated 352,000 tons of CO2 emissions each year. LoopWorks estimates a total addressable market (TAM) of $1T, or 150 units of coverage, making PRT a high-impact solution with gigaton-scale drawdown potential in a global market.
That estimate of 352,000 tons of CO2 emissions abated each year comes from the following extrapolation. The dual-loop PRT system will serve an area of 1.4 sq-miles, which is 10% of the entire 14.2 square-miles encompassed by Milpitas city limits. Although population density is higher in the PRT area, we will use 10% of the entire city and its population to represent the area to be served. During 2019, Milpitas service stations sold 26,306,367 gallons of gasoline, so roughly 2,630,636 gallons were bought and burned by service-area residents.
If just 20% of their gas-powered trips switched to PRT and other alternatives, then PRT will prevent the burning of 526,126 gallons per year – or 4930 tons of CO2 emissions each year (18.74 lbs/gallon X 526,126 gal. X ton/2000 lbs). Similar factors applied to a 100 sq-mi area – a single unit – would be 71.4 times as much, or 352,000 tons of CO2 emissions abated each year.
Embedded Carbon
Every vehicle, whether a car or a PRT cab, has embedded carbon that was required to manufacture it. Rather than electrify 3000-lb. privately-owned cars that sit idle 95% of the time, PRT electrifies a high-use, community-shared system of light-weight (1000 lbs.) cabs which are used frequently throughout the day. By reducing the need for personal cars, fewer will be owned - which will reduce the concomitant embedded carbon.
What would an analysis of carbon embedded in transportation infrastructures show? Most likely, it would reveal that PRT guideways and stations contain less embedded carbon than other forms of transportation infrastructure.
Second-Order / Knock-On Effects
PRT reduces CO2 emissions directly by replacing fossil-fueled car trips, and indirectly by replacing cars and their embedded carbon. Surprisingly, a third category of knock-on effects may produce even bigger reductions.
Most trips in Milpitas currently utilize a car. A dozen studies show that the synergy of PRT with other existing transportation options will dramatically increase transit ridership by 100% and more. These trips that previously would be taken with a car can be counted toward PRT’s reduction in CO2 emissions.
Third Derivative’s use of Direct Mitigation Measures (DMMs) formalizes CO2 emissions reductions into 3 categories. DMM 1 emissions are reduced by using electricity to move people around as described above in Gigaton Reductions in Carbon Emissions.
DMM 2 are efficiency-improving solutions that reduce resource consumption, and recognize we live in a world of resource limits that requires innovative and frugal ways of using those resources. For example, rather than electrify privately-owned cars that sit idle 95% of the time, PRT electrifies high-use, community-shared transit cabs that offer quick, efficient trips around the service area. Also, the ridership boom described below increases utilization of existing transit assets making them more energy efficient per passenger mile.
DMM 3 is an “add-on” product/service that improves the performance of another low- or net-zero-GHG solution. PRT is a catalyst technology that, like cell phones, creates unimagined opportunities for new ways of doing things.
For example, a dozen studies concluded that transit ridership would grow by 100% or more when PRT is added to the existing transit mix. (Factors driving these results are described in PRT Induces Synergy in Transit Ridership.) Likewise, PRT guideways that span travel barriers will induce far more walking and rolling trips (whether "active" or electric). And, it won't be long before a human-moving PRT system starts moving freight, recyclable materials, and garbage. All these knock-on effects lead to more reductions in CO2 emissions.
PRT infrastructure also presents an opportunity to add solar-electric panels atop stations and between supporting posts. Conduits within the guideways provide for electrical transmission from those solar panels to storage batteries.
Fewer transportation dollars leaving the community, and more property tax dollars flowing to public agencies, increases capital available for investing in clean energy technologies. Local transit agencies with increased ridership/fares could increase service or reduce the need for taxpayer subsidies.
Taken together, these knock-on effects of PRT may produce even bigger reductions in CO2 emissions than the direct replacement of car trips with PRT trips. Imagine combining this potential with PRT's ability to grow locally, be replicated virally, and scale to serve large metropolitan areas. The impact could be more than just a $1T PRT industry.
Additional Environmental/Nature Benefits
While PRT technology promises a huge reduction in CO2 emissions that will help reverse Global Warming, it will also bring these positive environmental benefits:
- By replacing car trips, PRT dramatically reduces other pollutants from automobiles (toxic fossil-fuel fumes and particulates, brake lining dust, lubrication leaks, tire particles, etc.).
- High-pressure, pneumatic tires rolling on smooth steel plates inside guideway cowling virtually eliminate noise.
- Developing higher-density communities and preserving natural areas is easier with PRT because 1) fewer roads and parking spaces are needed in new developments, and 2) PRT can be deployed in established areas due to its ease of routing and installation. PRT's minimal need for land also creates opportunities to reduce energy-wasting congestion where no space exists for traditional alternatives.
- As a tool in responding to natural disasters, PRT is resilient to all kinds of weather except for extremely high winds. As an elevated system, PRT can continue operating in flooded areas.
- Wildlife preservation: ground-roaming animals are safe from elevated PRT, while flying creatures are safer due to slower, smaller cabs.
- Water retention could increase dramatically due to reduced need for impervious surfaces (roads/parking).
- Land Savings: PRT requires only very small, widely-separated land plots instead of wide, continuous strips of land. Thus, the percentage of land required for PRT is about 0.02% vs. 30-70% for the automobile system. Replacing some roads with PRT will preserve or liberate land for parks, pedestrian trails, bike lanes, and other uses. The following sequence of 4 images graphically shows how much space becomes available when bi-directional High-Capacity PRT is substituted for a 6-lane freeway.
