One of the arguments transit advocates regularly use to justify the billions spent by taxpayers every year on mass transit is that it reduces greenhouse gas (GHG) emissions. However, the data is clear that its actual effect on GHG emissions is negligible.

The easiest way to demonstrate this is through a thought experiment that assumes all trips currently made in passenger vehicles could be converted to transit. Of course, it is impossible to convert every passenger trip to transit, but the exercise will give us the outside limit of how much transit could reduce GHG emissions.

The EPA has issued a report that estimated the total U.S. GHG emissions as 2022 at 6,343 metric tons and breaks down the sources of those emissions. Transportation makes up 29% of the total.  Of the total emissions attributed to transportation, the EPA estimates that 57% are due to “light-duty vehicles.” It attributes 20% to passenger vehicles and 37% to “light-duty trucks, which include sport utility vehicles, pickup trucks, and minivans.”

The EPA lumping all light-duty trucks into the same category creates some difficulty in estimating potential savings from transit. Many families use SUVs, pickups and minivans as passenger vehicles. But many light-duty trucks are also used by businesses for deliveries and service calls. Those trips cannot be converted to transit.

But for the purposes of this thought experiment, I am going to assume that all of the light-duty truck use could be converted to transit, which is clearly a gross overestimation. Making that assumption, the total share of GHG emissions from all light-duty vehicles is 16.5% (29% x 57%).

However, mass transit is not GHG emission free. So, the next thing we need to know is how much the various modes of mass transit reduce GHG emissions. This is a chart that was prepared by the Federal Transit Administration (FTA), showing the relative emissions for passenger cars compared to various modes of transit, and from which it concludes that transit would reduce GHG emissions from personal autos by over half (1-(.45/.96)=53%).

There are several things to note about this chart. The first is that tied for second in reducing emissions are van pools. Yet, in the balance of the FTA report it does not mention van pools again. All of its promotion of transit as a source of emission reductions is devoted to buses and trains. Of course, no one makes billions of dollars off organizing van pools.

The second important thing to note is that the chart uses GHG emissions per passenger-mile traveled. This is important because the amount of emissions per passenger-mile varies dramatically based on how many people are traveling together for each mode.

The FTA chart assumes various load factors ranging from 28%-56% for transit modes, but assumes that every car has only a single occupant. This is denoted by the parenthetical “SOV” under “Private Auto” column. However, if a private auto has two passengers, then its emissions would be .48 per passenger-mile or virtually the same as the average for all transit mode.

Further down in the report, it notes that for “general purpose” trips made in a private auto, the average number of passengers is 1.63. That reduces GHG emissions for private autos to .59, which is actually lower than buses. This means the average private auto trip in the U.S. actually emits less GHG per passenger-mile than bus transit does . . . something the FTA report conveniently omits.

So, the FTA’s comparisons are badly skewed, but for the purposes of continuing our thought experiment, let’s assume that the FTA numbers are accurate, and by moving every single passenger vehicle trip in the country to transit, it would reduce GHG emissions from personal automobile transportation by 53%. So now, the reduction would be 8.7% (29% x 57% x 53%) of total emissions. To put that number in some perspective, the EPA’s most current estimate of GHG inventories has a margin of -5% to 6% (see page ES-28).

In other words, if we eliminated every passenger automobile in the U.S. in favor of a transit alternative and use completely unrealistic assumptions, the total estimated reduction would be barely out of the margin of error for total estimated GHG emissions.

The negligible effect is even clearer when examined for specific projects. A great example is the claim made by Houston Metro in 2019 about the reduction in GHG emissions that would occur as result of its proposed “MetroNext” expansion. As part of its campaign to convince voters, Metro’s leadership made the following claim:

If you can read the tiny print at the bottom right of the page, Metro says the estimated GHG reductions were based on its “Regional Travel Demand Model.” That model was later completely discredited. For example, the ridership on the proposed University BRT per that model was later lowered by 75%. But even if we take the claim at face value, the alleged reduction is still inconsequential.

According to the Houston-Galveston Area Council, Climate Action Plan (see. p. 21), the total GHG emissions for the Houston region in 2021 was 233 million metric tonnes. That converts to 521 trillion pounds. So, Houston Metro’s contribution to the reduction of emissions in 2019 was .13% and even if Metro were to achieve the reduction it claimed from its massive, proposed expansion, the reduction would amount to .28% of the region’s total GHG emissions. Of course, the margin of error for Metro’s estimates or the HGAC inventory estimate would be many times higher than values.

There is little doubt in my mind that Metro intentionally stated the reduction in pounds instead of the standard tonnes, so that the number would appear larger. To the average person (i.e. voter), a billion-pound reduction sounds enormous if it is not put into the context of total regional emissions. Much of transit literature and especially the promotion of new transit projects is replete with this kind of misleading representations and outright bias in the presentation of the claimed benefits of transit.

I believe we need an efficient and effective transit system as part of the basic social safety net. Providing some mobility for those who cannot afford to own and operate their own vehicle and those who are physically not able to operate one is the right thing to do.  It also helps the local economy by providing a way for employees to get to their jobs.

But transit does little to relieve traffic congestion and virtually nothing to improve air quality. We need to start having an honest conversation about the purpose of transit and what we can reasonably expect it to accomplish. And we need to stop lying to the public and voters about fanciful, non-existent benefits.