LCC closes more frequently for avalanche control work than BCC as LCC has 64 slides paths, quite a few more than BCC. Since the advent of the Ikon Pass, BCC has had many closures of varying duration due to what UDOT calls "periods of extreme congestion". This occurs when all car parks fill up early, roadside parking within a couple miles or so of each resort gets maxed out, all backcountry car parks fill up, and gridlock ensues because the volume of vehicles heading up-canyon is unrelenting and traffic canyon-wide comes to a crawl. UDOT and UPD close down upbound traffic at the mouth and detain the remainder of upbound traffic at Reynolds Flat (roughly mid-canyon). Until a sufficient number of vehicles exit the canyon, nothing other than emergency vehicles, ski buses, and employee van pools are allowed to proceed up canyon. This situation can be as brief as an hour or last more than a couple or so hours. Exceptions to this occur when the snow is and has been pounding down or a bad accident has occurred somewhere in the canyon, bringing whatever traffic flow that had existed to a complete standstill. In that case, count on an indeterminable delay. BCC is about 6 miles longer than LCC so a greater number of vehicles can be accommodated. Two seasons ago a supervisor with UDOT told me BCC was experiencing about 1,000 more vehicles per day on average than LCC. Last season a UPD officer told me that number had increased to about 1,500 vehicles per day.
All that aside, a visit in mid-March would likely not coincide with the time periods with the highest likelihood of heavy canyon usage and closure, which are the Xmas - New Years Day holiday timeframe, MLK Day weekend, President's Day weekend, the majority of weekends between Xmas and early March (depending upon the seasonal abundance of snowfall and the timing of storms), plus powder days and days following heavy overnight snowfall at resort elevation.
If you're here in mid-March and staying in the valley during a heavy-snow cycle, get up the canyon early or in the line-up early. If you've been up the canyon(s) skiing during an all-day snowfall, consider leaving earlier than the masses or having dinner at the resort at the end of the day and delaying your descent down the canyon