Complex sentence: The purpose of this improvement was to reduce accidents on a stretch of road that now carries over 12,000 motorists per day, many headed for either the Pala Indian casino or a new gravel quarry that had recently opened.
Split into simpler sentences: The purpose of this improvement is to reduce accidents on a stretch of road that now carries over 12,000 motorists per day. Much of this traffic is destined for either the Pala Indian casino or a new gravel quarry that was recently opened.