# Ride-sharing during a pandemic is relatively safe

In short:
- Don't use Uber Pool, ride as a single passenger.
- Make sure all the windows are rolled down.
- The faster the car moves the lower your risk. At 50 mph and with both of you wearing masks, it's likely that your risk is lower than the risk of a trip to an indoor grocery store.
- The most important factor in managing your risk during a pandemic is reducing the number of people you are exposing yourself to. In the context of ride-sharing, it's possible that many different passengers have recently been in the car you are taking, treat every surface as if it was contaminated. From the moment you touch the door handle you should not touch your face until you can wash/sanitize your hands. The importance of this point depends on the incidence rate in your area.

Summarizing [this paper](https://arxiv.org/pdf/2007.03612.pdf) from July 8th:

- They ran CFD simulations of the airflows in a car with a single driver and a single passenger. They modeled a Toyota Prius driving at 50 mph. Speed plays a large role:

> Since the Reynolds number of the flow is high, the air flow patterns will be largely insensitive to how fast the car is driven. However, the air-changes-per-hour (ACH) is expected to depend linearly on the car speed and consequently, the slower the car speed, the lower the ACH, the longer the residence time in the cabin, and hence the higher the opportunity for pathogenic infection.

- In order to minimize transmission from driver to passenger, or from passenger to driver, all windows should be open. This protects both of you, but it protects the passenger more:

> As before, the lowest level of scalar transport corresponds to Config. 6 with all windows open, although we note that the concentration load here (about 2%), is noticeably higher than that for the driver-to-passenger transmission (about 0.2%)

A 98% reduction in concentration is a great deal! However, you are still exposing the driver to some risk. Multiplied over how many passengers a driver is likely to have, you should probably still wear a mask.

- The airflow breaks into two sections, the left side and the right side. To minimize exposure, sit in the rear passenger-side seat:


- "Air Changes per Hour" is a standard metric for comparing ventilation systems. Hospital rooms designed to house patients with airborne diseases perform 12 ACH, airplanes perform 20-30 ACH, keeping all the windows down at 50 mph gives you ~250 ACH. The particles you emit linger in the car for just 14 seconds. For a transmission to occur, someone would have to be continually dumping virus for an extended period of time. If you're taking a short trip and you're not yelling at each other (or singing together, that's also disallowed), driving in an Uber with your windows down is likely to be safer than going to your indoor grocery store.

There is a big caveat to this! When you take an Uber trip within the city, it's likely that you will spend most of that time traveling at under 50 mph. If, for example, you spend 15 minutes waiting at stop lights, that's still 15 minutes of exposure to someone less than 6 feet away from you. [Illinois would classify you](https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(20)30607-3/fulltext) as a "high-risk contact" when doing their contact tracing.

- Here's a neat counterintuitive finding: if you can't keep all the windows open, and could only pick 2 windows to open, pick the two windows furthest away from yourselves:


If you open the windows next to you, and the driver opens the window next to them, there is more transmission to you than there would be if you instead open the two windows furthest from yourselves.