Due to safety issues such as aquaplaning, the race is not held in wet conditions. In the event of a rain delay, the race will be postponed until rain showers cease, and the track is sufficiently dried. If rain falls during the race, officials can end the race and declare the results official if more than half of the scheduled distance (i.e., 101 laps) has been completed. The Indianapolis 500, as well as other IndyCar Series races, does not utilize the green – white – checker finish in case of a late-race yellow. The race can be (and in the past has been) finished under caution. However, officials may call for a late-race red flag to ensure a green-flag finish, an option that was used in 2014 and 2019. The circuit lacks lights, therefore lateness can become a factor in the cases of lengthy delays.
The traditional 33-car starting field at Indianapolis is larger than the fields at the other IndyCar races. The field at Indy typically consists of all of the full-time IndyCar Series entries (roughly 20–22 cars), along with 10–15 part-time or “Indy-only” entries. The “Indy-only” entries, also known as “One-Offs”, may be an extra car added to an existing full-time team, or a part-time team altogether that does not enter any of the other races, or enters only a few selected races. The “Indy-only” drivers may come from a wide range of pedigrees but are usually experienced Indy car competitors that either lack a full-time ride, are former full-time drivers that have elected to drop down to part-time status, or occasional one-off drivers from other racing disciplines. It is not uncommon for some drivers (particularly former Indy 500 winners) to quit full-time driving during the season, but race at Indy singly for numerous years afterward before entering full retirement.