Answer by taking a quote from the following article:

The Houston Livestock Show and Rodeo, also called RodeoHouston or abbreviated HLSR, is the largest livestock exhibitions and rodeo in the world. It also includes one of the richest regular-season rodeo events. It has been held at NRG Stadium in Houston, Texas, since 2003. It was previously held in the Astrodome.

Since 1952, traditional trail rides have been a part of the Houston Livestock Show and Rodeo. As of 2017, there were 13 official trail rides, totaling over 3,000 riders. The trail rides range in size from a dozen to over one thousand people who ride on horseback or in horse-drawn wagons from various areas of the state to Houston. They make their way at about 3 miles (4.8 km) per hour, covering up to 17 miles (27 km) each day. Many of the routes take place in part along major highways and busy city streets, making safety a major concern.  The trail rides last from a few days to three weeks, depending on the distance they cover. Some of the participants are able to join only on weekends or at the end of the trip. The days start very early, and often end with live music or a small celebration. Many riders choose to camp in recreational vehicles rather than in the open. Each morning, they drive their vehicles and horse trailers to the next camping spot, then have a bus or convoy take them back so they can retrace their path on horseback. Participants can bring their own provisions, or, in some cases, purchase meals at a chuck wagon that is also following the trail.  The rides converge at Memorial Park in Houston on Go Texan Day, the Friday before the livestock show and rodeo begins. The city closes some roads downtown to allow the riders to reach their destination safely. The resulting traffic interruption cause annual complaints from those who work downtown. The following day, all of the trail riders participate in the parade.

are the trail rides open to the public?
As of 2017, there were 13 official trail rides, totaling over 3,000 riders.