Tomorrow, Sunday, is the main race of the Las Vegas Grand Prix. Downtown streets will be severely interrupted. Don't park in the confines of the race, if you will need to get out. The race will be (roughly) 1pm to 330 pm, and will be televised nationally - we will see how complete that saturation is.
The race is downtown, not at all near the Welcome sign on The Strip. This photo shows a wider view of the welcome sign, and that it is very common for people to walk up to it and take pictures.