Have you ever wondered about the air flow on RTD’s light rail cars?

From the questions that our customer care team are fielding, it’s clear that many of you are thinking about the circulation and quality of the air inside our vehicles as riders return to our system. It’s a legitimate question amid a pandemic. The Centers for Disease Control and Prevention have stated that key ways to protect individuals and slow the spread of the novel coronavirus include ensuring that ventilation systems operate properly, as well as improving ventilation by increasing the percentage of outside air or total air flow to occupied spaces. 

“When considering the COVID-19 pandemic, it is the industry’s understanding that people are less likely to contract the virus when they are in a fresh-air, outside environment,” said Phil Eberl, general superintendent of light rail vehicle maintenance. “RTD helps emulate that condition inside our rail cars by opening the doors on both sides of the vehicle at every station.” 

As RTD’s dedicated team continues to deliver more than 140,000 trips each weekday across our system, we wanted to provide you with information about the air you breathe when riding light rail. 

The air inside each rail car is fully exchanged every 59 seconds. The ratio of fresh air to recirculated air is about 25% versus 75%. Every minute, about 750 cubic feet of fresh air enters the passenger compartment with all doors closed. The rail car manufacturer recommends increasing fresh airflow into the rail cars as much as possible. 

Recirculated air in RTD vehicles is filtered using 2-inch-thick pleated panel air filters at the two return-air grilles on either end of the passenger compartment. RTD changes the air filters inside its rail cars every 3 weeks. By comparison, it’s recommended that air filters in homes be changed every 3 months. 

These filters carry a minimum efficiency reporting value (MERV) rating of 7 or 8, trapping particles down to 3 microns in size. Such particles include pollen, dust mites and mold. You may wonder: Why not upgrade to a higher-rated MERV filter or an air filter with a higher rating, such as a high-efficiency particulate air (HEPA) filter, which captures viral particles? They are costly, require a pre-filter or replacement intervals that are too frequent, and would slow down the air-flow and air exchange rate.

Eberl added: “Spending millions of dollars on supplemental conditioning systems such as ionization of the air particles or irradiation of the air has not been proven to RTD to provide a healthier environment for our customers during a ride on a light rail vehicle, and thereby do not meet the cost benefit considerations for the investment.”

In the event that the health department issues a serious air quality warning, RTD could allow passengers to use a push button to open each door themselves, which would increase the amount of conditioned air in the passenger compartment while still providing an acceptable air exchange rate.

Like fellow transit agencies across the country, RTD is exploring best practices for cleaning its vehicles and the air inside them. The American Public Transportation Association (APTA) in June published a white paper detailing current industry practices for cleaning and disinfecting transit vehicles and facilities in response to a pandemic. RTD is taking many of the measures that are described. In August, the agency began sanitizing vehicles daily with electrostatic sprayers, allowing maintenance workers to sanitize a vehicle with hospital-grade disinfectant in just 5 minutes. The technology provides three times more coverage in the same amount of time than traditional spray bottles, buckets and rags.

Every day, RTD’s light rail maintenance cleaning team cleans and disinfects our rail cars, including the floors, step wells, hand railings, hand straps, doors, ceilings and walls.

During the pandemic, Eberl and his team are committed to ensuring that RTD riders are as safe on our system as anywhere outside of their home. 

“The air quality and cleanliness of our vehicles is among the best in the country,” Eberl said. “Our HVAC systems, with the filtering and exchange of the air, are more than adequate to provide a healthy environment for our customers, provided we all follow the pandemic mask and distancing guidelines of the state.”