The Labor Day weekend is one of the busiest of the year for mountain traffic on Interstate 70, rivaling ski traffic on the weekends of the Martin Luther King holiday and Presidents Day, but if the mountains are calling and you must go, here’s a tip: Sunday might be your best bet. Last year, for example, westbound traffic through the Eisenhower/Johnson tunnels the day before Labor Day was just over 20,000 vehicles, as compared to more than 34,200 on Friday and nearly 30,000 on Saturday, according to CDOT.