The cones were removed from the westbound lanes between Interstate 225 and Colorado Boulevard around 3 a.m.
Fees will be waived during the testing period.
CDOT said the express lanes will result in a 20-to-50% time savings for drivers in all travel lanes. Eventually, the express lanes will extend from I-25 to Chambers Road, east and westbound.
Testing of the eastbound express lanes will begin June 17.
Work on the Central 70 Project began in September of 2018. Most of the work is expected to be finished early next year.
The cost of rebuilding the interstate through Denver is $1.2 billion dollars.