Crews are hoping to reach a big milestone on the Twin Tunnels expansion project on Interstate 70 Monday.
Before dawn, crews set off an explosion at the exit point of the westbound tunnel.
"Plenty of air horns went off before," 7NEWS Reporter Tyler Lopez said. "Three quick horns were heard right before the blast."
A final blast was expected later in the morning but was canceled.
TwinTunnels: Blasting done. Early. 4:30am was the final blast on Westbound bore near IdahoSprings. 6:30 cancelled. pic.twitter.com/3h6XU6Beee— Tyler Lopez (@nonstopTLo) August 18, 2014
The westbound side is being widened as part of a $55 million package of improvements that will eventually add a third lane.
The goal is to reduce weekend traffic delays on weekends.
The eastbound side is done and is already handling both directions of traffic.
The larger, improved tunnel is expected to open by the end of the year.